Location: Beeler, Reuter, 1977 @ 506b287da784 / beeler_reuter_1977.cellml

Author:
pmr2.import <nobody@models.cellml.org>
Date:
2008-01-24 21:47:30+13:00
Desc:
committing version05 of beeler_reuter_1977
Permanent Source URI:
https://models.cellml.org/workspace/beeler_reuter_1977/rawfile/506b287da78431f2bdba8a667eb4d9474ca4e666/beeler_reuter_1977.cellml

<?xml version='1.0' encoding='utf-8'?>
<!-- FILE : beeler_reuter_mammalian_ventricle_1977.xml

CREATED : September 2001

LAST MODIFIED : 5th April 2003

AUTHOR : Catherine Lloyd
         Department of Engineering Science
         The University of Auckland
         
MODEL STATUS : This model conforms to the CellML 1.0 Specification released on
10th August 2001, and the 16/01/2002 CellML Metadata 1.0 Specification.

DESCRIPTION : This file contains a CellML description of the mammalian
ventricular action potential, based on the Beeler-Reuter model, 1977. 

CHANGES: 
  19/10/2001 - CML - Removed document type definition as this is declared as
                     optional according to the WC3 recommendation.  
  24/10/2001 - CML - Made changes to some of the metadata, bringing them up to
                     date with the most recent working draft (26th September) of
                     the Metadata specification.
  07/12/2001 - CML - Changed some equations after using the MathML validator.
  21/01/2002 - AAC - Updated metadata to conform to the 16/01/02 CellML Metadata
                     1.0 Specification.
  28/02/2002 - CML - Corrected the membrane voltage differential equation.
  19/07/2002 - CML - Added more metadata.
  05/04/2003 - AAC - Changed the model name so the model loads in the database 
                     easier.
--><model xmlns="http://www.cellml.org/cellml/1.0#" xmlns:cmeta="http://www.cellml.org/metadata/1.0#" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:bqs="http://www.cellml.org/bqs/1.0#" xmlns:cellml="http://www.cellml.org/cellml/1.0#" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:vCard="http://www.w3.org/2001/vcard-rdf/3.0#" xmlns:ns7="http://www.cellml.org/metadata/simulation/1.0#" cmeta:id="beeler_reuter_1977_version04" name="beeler_reuter_1977_version04">
  
  
  <!--
    Below, we define some additional units for association with variables and
    constants within the model. The identifiers are fairly self-explanatory.
  -->
<documentation xmlns="http://cellml.org/tmp-documentation">
<article>
  <articleinfo>
  <title>Beeler-Reuter Mammalian Ventricular Model 1977</title>
  <author>
    <firstname>Catherine</firstname>
          <surname>Lloyd</surname>
    <affiliation>
      <shortaffil>Bioengineering Institute, University of Auckland</shortaffil>
    </affiliation>
  </author>
</articleinfo>
  <section id="sec_status">
    <title>Model Status</title>
    <para>
        This model has been curated and is known to run and reproduce the published results in PCEnv and COR. A PCEnv session file is also associated with this model.
          </para>
  </section>
  <sect1 id="sec_structure">
<title>Model Structure</title>

<para>
In contrast to the earlier Purkinje fibre ionic current models of <ulink url="${HTML_EXMPL_N_MODEL}">D. Noble (1962)</ulink> and <ulink url="${HTML_EXMPL_MNT_MODEL}">R.E. McAllister, D. Noble and R.W. Tsien (1975)</ulink>, the G.W. Beeler and H. Reuter 1977 model was developed to describe the mammalian ventricular action potential.  Not all the ionic currents of the Purkinje fibre model are present in ventricular tissue; therefore, this model is simpler than the MNT model.  The total ionic flux is divided into only four discrete, individual ionic currents (see <xref linkend="fig_cell_diagram"/> below).  The main additional feature of the Beeler-Reuter ionic current model is a representation of the intracellular calcium ion concentration.
</para>

<para>
The complete original paper reference is cited below:
</para>

<para>
Reconstruction of the action potential of ventricular myocardial fibres, Beeler, G.W. and Reuter, H. 1977 <ulink url="http://www.jphysiol.org/">
            <emphasis>Journal of Physiology</emphasis>
          </ulink>, 268, 177-210.  <ulink url="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&amp;db=PubMed&amp;list_uids=874889&amp;dopt=Abstract">PubMed ID: 874889</ulink>
</para>

<informalfigure float="0" id="fig_cell_diagram">
<mediaobject>
  <imageobject>
    <objectinfo>
      <title>cell diagram of the Beeler-Reuter model showing ionic currents across the cell surface membrane</title>
    </objectinfo>
    <imagedata fileref="beeler_reuter_1977.png"/>
  </imageobject>
</mediaobject>
<caption>A schematic diagram describing the current flows across the cell membrane that are captured in the BR model.</caption>
</informalfigure>

<informalfigure float="0" id="fig_cellml_rendering">
<mediaobject>
  <imageobject>
    <objectinfo>
      <title>the cellml rendering of the Beeler-Reuter model</title>
    </objectinfo>
    <imagedata fileref="cellml_rendering.gif"/>
  </imageobject>
</mediaobject>
<caption>The network defined in the CellML description of the Beeler-Reuter model. A key describing the significance of the shapes of the components and the colours of the connections between them is in the <ulink url="http://www.cellml.org/tutorial/notation/?searchterm=notation%20guide">notation guide</ulink>.  For simplicity, not all the variables are shown.</caption>
</informalfigure>

<para>
The membrane physically contains the currents as indicated by the blue arrows in <xref linkend="fig_cellml_rendering"/>. The currents act independently and are not connected to each other. Several of the channels encapsulate <emphasis>and</emphasis> contain further components which represent activation and inactivation gates. The addition of an encapsulation relationship informs modellers and processing software that the gates are important parts of the current model. It also prevents any other components that aren't also encapsulated by the parent component from connecting to its gates, effectively hiding them from the rest of the model.
</para>

<para>
The breakdown of the model into components and the definition of encapsulation and containment relationships between them is somewhat arbitrary. When considering how a model should be broken into components, modellers are encouraged to consider which parts of a model might be re-used and how the physiological elements of the system being modelled are naturally bounded. Containment relationships should be used to provide simple rendering information for processing software (ideally, this will correspond to the layout of the physical system), and encapsulation should be used to group sets of components into sub-models.
</para>

</sect1>
</article>
</documentation>

  <units name="ms">
    <unit units="second" prefix="milli"/>
  </units>
  
  <units name="per_ms">
    <unit units="second" prefix="milli" exponent="-1"/>
  </units>

  <units name="mV">
    <unit units="volt" prefix="milli"/>
  </units>

  <units name="per_mV">
    <unit units="volt" prefix="milli" exponent="-1"/>
  </units>
  
  <units name="per_mV_ms">
    <unit units="mV" exponent="-1"/>
    <unit units="ms" exponent="-1"/>
  </units>
  
  <units name="mS_per_mm2">
    <unit units="siemens" prefix="milli"/>
    <unit units="metre" prefix="milli" exponent="-2"/>
  </units>

  <units name="uF_per_mm2">
    <unit units="farad" prefix="micro"/>
    <unit units="metre" prefix="milli" exponent="-2"/>
  </units>

  <units name="uA_per_mm2">
    <unit units="ampere" prefix="micro"/>
    <unit units="metre" prefix="milli" exponent="-2"/>
  </units>
  
  <units name="concentration_units">
    <unit units="mole" prefix="nano"/>
    <unit units="metre" prefix="milli" exponent="-3"/>
  </units>
    
  <units name="per_concentration_units">
    <unit units="concentration_units" exponent="-1"/>
  </units>

  <!--
    The "environment" component is used to declare variables that are used by
    all or most of the other components, in this case just "time".
  -->
  <component name="environment" cmeta:id="environment">
    
    <variable units="ms" public_interface="out" name="time" cmeta:id="environment_time"/>
  </component>

  <!--
    The "membrane" component is really the `root' node of our model.
    It defines the action potential variable "V" among other things.
  -->
  <component name="membrane" cmeta:id="membrane">
    

    <!-- These variables are defined here and used in other components. -->
    <variable units="mV" public_interface="out" cmeta:id="membrane_V" name="V" initial_value="-84.624"/>
    
    <!-- This variable is defined here and only used internally. -->
    <variable units="uF_per_mm2" cmeta:id="membrane_C" name="C" initial_value="0.01"/>
    
    <!-- These variables are imported from other components. -->
    <variable units="ms" public_interface="in" name="time"/>
    <variable units="uA_per_mm2" public_interface="in" name="i_Na"/>
    <variable units="uA_per_mm2" public_interface="in" name="i_s"/>
    <variable units="uA_per_mm2" public_interface="in" name="i_x1"/>
    <variable units="uA_per_mm2" public_interface="in" name="i_K1"/>
    <variable units="uA_per_mm2" public_interface="in" name="Istim"/>
    
    <!--
      The membrane voltage (V) is calculated as an ordinary
      differential equation in terms of the currents.
    -->
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="membrane_voltage_diff_eq">
      <apply id="membrane_voltage_diff_eq">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> V </ci>
        </apply>
        <apply>
          <divide/>
          <apply>
            <minus/>
            <ci>Istim</ci>
            <apply>
              <plus/>
              <ci> i_Na </ci>
              <ci> i_s </ci>
              <ci> i_x1 </ci>
              <ci> i_K1 </ci>
            </apply>
          </apply>
          <ci>C</ci>
        </apply>
      </apply>
    </math>

    
    
    
  </component>
     
  <!--
    The "sodium_current" component contains the differential equations
    governing the influx of sodium ions through the cell surface membrane into  
    the cell.  This sodium current is primarily responsible for the rapid       
    upstroke of the action potential during membrane depolarisation.
    Note that no initial values are needed on many variables as they are
    all directly dependent on the membrane voltage.
  -->
  <component name="sodium_current" cmeta:id="sodium_current">
    
    <!-- This variable is defined here and used in other components. -->
    <variable units="uA_per_mm2" public_interface="out" name="i_Na" cmeta:id="sodium_current_i_Na"/>

    <!-- These variables are defined here and only used internally. -->
    <variable units="mS_per_mm2" cmeta:id="sodium_current_g_Na" name="g_Na" initial_value="4.0e-2"/>
    <variable units="mV" cmeta:id="sodium_current_E_Na" name="E_Na" initial_value="50.0"/>
    <variable units="mS_per_mm2" cmeta:id="sodium_current_g_Nac" name="g_Nac" initial_value="3.0e-5"/>
    
    <!-- 
      Time is imported from the environment, and membrane potential is
      imported from the membrane component.  These variables are used in the 
      "sodium_current" parent component, which also acts as an interface, 
      passing the variables to its encapsulated gate components.
    -->
    <variable units="ms" public_interface="in" private_interface="out" name="time"/>
    <variable units="mV" public_interface="in" private_interface="out" name="V"/>
    
    <!-- These variables are imported from encapsulated components. -->
    <variable units="dimensionless" private_interface="in" name="m"/>
    <variable units="dimensionless" private_interface="in" name="h"/>
    <variable units="dimensionless" private_interface="in" name="j"/>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="i_Na_calculation_eq">
      <!--
        The following equation calculates the sodium current in terms
        of the conductance, the membrane voltage, and the gate variables.
      -->
      <apply id="i_Na_calculation">
        <eq/>
        <ci> i_Na </ci>
        <apply>
          <times/>
          <apply>
            <plus/>
            <apply>
              <times/>
              <ci> g_Na </ci>
              <apply>
                <power/>
                <ci> m </ci>
                <cn cellml:units="dimensionless"> 3.0 </cn>
              </apply>
              <ci> h </ci>
              <ci> j </ci>
            </apply>
            <ci> g_Nac </ci>
          </apply>
          <apply>
            <minus/>
            <ci> V </ci>
            <ci> E_Na </ci>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
     
  <!--
    The "sodium_current_m_gate" is the m gate encapsulated inside the sodium
    current 
  -->
  <component name="sodium_current_m_gate" cmeta:id="sodium_current_m_gate">
    

    <!-- This variable is defined here and used in other components. -->
    <variable units="dimensionless" public_interface="out" cmeta:id="sodium_current_m_gate_m" name="m" initial_value="0.011"/>
        
    <!-- These variables are defined here and only used internally. -->
    <variable units="per_ms" name="alpha_m" cmeta:id="sodium_current_m_gate_alpha_m"/>
    <variable units="per_ms" name="beta_m" cmeta:id="sodium_current_m_gate_beta_m"/>
        
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="mV" public_interface="in" name="V"/>
    <variable units="ms" public_interface="in" name="time"/>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="alpha_m_calculation_eq">
      <!--
        The rate constants on the m and h gates are functions
        of membrane voltage.
      -->
      <apply id="alpha_m_calculation">
        <eq/>
        <ci> alpha_m </ci>
        <apply>
          <divide/>
          <apply>
            <times/>
            <cn cellml:units="per_mV_ms"> -1 </cn>
            <apply>
              <plus/>
              <ci> V </ci>
              <cn cellml:units="mV"> 47.0 </cn>
            </apply>
          </apply>
          <apply>
            <minus/>
            <apply>
              <exp/>
              <apply>
                <times/>
                <cn cellml:units="per_mV"> -0.1 </cn>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 47.0 </cn>
                </apply>
              </apply>
            </apply>
            <cn cellml:units="dimensionless"> 1.0 </cn>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="beta_m_calculation_eq">
      <apply id="beta_m_calculation">
        <eq/>
        <ci> beta_m </ci>
        <apply>
          <times/>
          <cn cellml:units="per_ms"> 40.0 </cn>
          <apply>
            <exp/>
            <apply>
              <times/>
              <cn cellml:units="per_mV"> -0.056 </cn>
              <apply>
                <plus/>
                <ci> V </ci>
                <cn cellml:units="mV"> 72.0 </cn>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="dm_dt_eq">
      <apply id="dm_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> m </ci>
        </apply>
        <apply>
          <minus/>
          <apply>
            <times/>
            <ci> alpha_m </ci>
            <apply>
              <minus/>
              <cn cellml:units="per_mV"> 1.0 </cn>
              <ci> m </ci>
            </apply>
          </apply>
          <apply>
            <times/>
            <ci> beta_m </ci>
            <ci> m </ci>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
  
  
  <!--
    The "sodium_current_h_gate" component is the h gate encapsulated in
    the sodium current.
  -->
  <component name="sodium_current_h_gate" cmeta:id="sodium_current_h_gate">
    
    <!-- This variable is defined here and used in other components. -->
    <variable units="dimensionless" public_interface="out" cmeta:id="sodium_current_h_gate_h" name="h" initial_value="0.988"/>
        
    <!-- These variables are defined here and only used internally. -->
    <variable units="per_ms" name="alpha_h" cmeta:id="sodium_current_h_gate_alpha_h"/>
    <variable units="per_ms" name="beta_h" cmeta:id="sodium_current_h_gate_beta_h"/>
    
    
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="mV" public_interface="in" name="V"/>
    <variable units="ms" public_interface="in" name="time"/>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="alpha_h_calculation_eq">
      <apply id="alpha_h_calculation">
        <eq/>
        <ci> alpha_h </ci>
        <apply>
          <times/>
          <cn cellml:units="per_ms"> 0.126 </cn>
          <apply>
            <exp/>
            <apply>
              <times/>
              <cn cellml:units="per_mV"> -0.25 </cn>
              <apply>
                <plus/>
                <ci> V </ci>
                <cn cellml:units="mV"> 77.0 </cn>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="beta_h_calculation_eq">
      <apply id="beta_h_calculation">
        <eq/>
        <ci> beta_h </ci>
        <apply>
          <divide/>
          <cn cellml:units="per_ms"> 1.7 </cn>
          <apply>
            <plus/>
            <apply>
              <exp/>
              <apply>
                <times/>
                <cn cellml:units="per_mV"> -0.082 </cn>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 22.5 </cn>
                </apply>
              </apply>
            </apply>
            <cn cellml:units="dimensionless"> 1.0 </cn>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="dh_dt_eq">
      <apply id="dh_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> h </ci>
        </apply>
        <apply>
          <minus/>
          <apply>
            <times/>
            <ci> alpha_h </ci>
            <apply>
              <minus/>
              <cn cellml:units="dimensionless"> 1.0 </cn>
              <ci> h </ci>
            </apply>
          </apply>
          <apply>
            <times/>
            <ci> beta_h </ci>
            <ci> h </ci>
          </apply>
        </apply>
      </apply>  
    </math>
  </component>
  
  <!--
    The "sodium_current_j_gate" component is the j gate encapsulated in
    the sodium current.
  -->
  <component name="sodium_current_j_gate" cmeta:id="sodium_current_j_gate">
    
    
    <!-- This variable is defined here and used in other components. -->
    <variable units="dimensionless" public_interface="out" cmeta:id="sodium_current_j_gate_j" name="j" initial_value="0.975"/>
        
    <!-- These variables are defined here and only used internally. -->
    <variable units="per_ms" name="alpha_j" cmeta:id="sodium_current_j_gate_alpha_j"/>
    <variable units="per_ms" name="beta_j" cmeta:id="sodium_current_j_gate_beta_j"/>
    
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="mV" public_interface="in" name="V"/>
    <variable units="ms" public_interface="in" name="time"/>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="alpha_j_calculation_eq">
      <apply id="alpha_j_calculation">
        <eq/>
        <ci> alpha_j </ci>
        <apply>
          <divide/>
          <apply>
            <times/>
            <cn cellml:units="per_ms"> 0.055 </cn>
            <apply>
              <exp/>
              <apply>
                <times/>
                <cn cellml:units="per_mV"> -0.25 </cn>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 78.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
          <apply>
            <plus/>
            <apply>
              <exp/>
              <apply>
                <times/>
                <cn cellml:units="per_mV"> -0.2 </cn>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 78.0 </cn>
                </apply>
              </apply>
            </apply>
            <cn cellml:units="dimensionless"> 1.0 </cn>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="beta_j_calculation_eq">
      <apply id="beta_j_calculation">
        <eq/>
        <ci> beta_j </ci>
        <apply>
          <divide/>
          <cn cellml:units="per_ms"> 0.3 </cn>
          <apply>
            <plus/>
            <apply>
              <exp/>
              <apply>
                <times/>
                <cn cellml:units="per_mV"> -0.1 </cn>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 32.0 </cn>
                </apply>
              </apply>
            </apply>
            <cn cellml:units="dimensionless"> 1.0 </cn>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="dj_dt_eq">
       <apply id="dj_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> j </ci>
        </apply>
        <apply>
          <minus/>
          <apply>
            <times/>
            <ci> alpha_j </ci>
            <apply>
              <minus/>
              <cn cellml:units="dimensionless"> 1.0 </cn>
              <ci> j </ci>
            </apply>
          </apply>
          <apply>
            <times/>
            <ci> beta_j </ci>
            <ci> j </ci>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
  
  <!-- The "slow_inward_current " component contains the differential           
   equations governing the transient inward ionic current.  This current is     
   predominately carried by calcium ions and it is largely responsible for      
   maintaining the plateau of the action potential. -->
  <component name="slow_inward_current" cmeta:id="slow_inward_current">
    

    <!-- This variable is defined here and used in other components. -->
    <variable units="uA_per_mm2" public_interface="out" name="i_s" cmeta:id="slow_inward_current_i_s"/>
 
    <!-- These variables are defined here and only used internally. -->
    <variable units="mS_per_mm2" cmeta:id="slow_inward_current_g_s" name="g_s" initial_value="9.0e-4"/>
    <variable units="mV" name="E_s" cmeta:id="slow_inward_current_E_s"/>
    <variable units="concentration_units" cmeta:id="slow_inward_current_Cai" name="Cai" initial_value="1.0e-4"/>
    
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="ms" public_interface="in" private_interface="out" name="time"/>
    <variable units="mV" public_interface="in" private_interface="out" name="V"/>
    
    <!-- These variables are imported from encapsulated components. -->
    <variable units="dimensionless" private_interface="in" name="d"/>
    <variable units="dimensionless" private_interface="in" name="f"/>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="E_s_calculation_eq">
      <!--
        The following equation determines the reversal potential of the
        slow inward current.
      -->
      <apply id="E_s_calculation">
        <eq/>
        <ci> E_s </ci>
        <apply>
          <minus/>
          <cn cellml:units="mV"> -82.3 </cn>
          <apply>
            <times/>
            <cn cellml:units="mV"> 13.0287 </cn>
            <apply>
              <ln/>
              <apply>
                <times/>
                <ci> Cai </ci>
                <cn cellml:units="per_concentration_units">0.001</cn>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="i_s_calculation_eq">
      <!--
        The following equation calculates the slow inward current in terms of   
        the conductance, the membrane voltage and the gate variables.
      -->
      <apply id="i_s_calculation">
        <eq/>
        <ci> i_s </ci>
        <apply>
          <times/>
          <ci> g_s </ci>
          <ci> d </ci>
          <ci> f </ci>
          <apply>
            <minus/>
            <ci> V </ci>
            <ci> E_s </ci>
          </apply>
        </apply>
      </apply>
    </math>
      
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="dCai_dt_eq">
      <!--  Change in {Ca}i (intracellular calcium concentration) is given in   
            terms of the slow inward current as: -->
      <apply id="dCai_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> Cai </ci>
        </apply>
        <apply>
          <plus/>
          <apply>
            <times/>
            <cn cellml:units="dimensionless"> -0.01 </cn>
            <ci> i_s </ci>
          </apply>
          <apply>
            <times/>
            <cn cellml:units="dimensionless"> 0.07 </cn>
            <apply>
              <minus/>
              <cn cellml:units="dimensionless"> 0.0001 </cn>
              <ci> Cai </ci>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
          
  <!--
    The "slow_inward_current_d_gate" component is the d gate encapsulated in
    the slow inward current.
  -->
  <component name="slow_inward_current_d_gate" cmeta:id="slow_inward_current_d_gate">
    

    <!-- This variable is defined here and used in other components. -->
    <variable units="dimensionless" public_interface="out" cmeta:id="slow_inward_current_d_gate_d" name="d" initial_value="0.003"/>

    <!-- These variables are defined here and only used internally. -->
    <variable units="per_ms" name="alpha_d" cmeta:id="slow_inward_current_d_gate_alpha_d"/>
    <variable units="per_ms" name="beta_d" cmeta:id="slow_inward_current_d_gate_beta_d"/>
    
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="mV" public_interface="in" name="V"/>
    <variable units="ms" public_interface="in" name="time"/>

    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="alpha_d_calculation_eq">
      <!--
        The rate constants on the d gate are functions of membrane voltage.
      -->
      <apply id="alpha_d_calculation">
        <eq/>
        <ci> alpha_d </ci>
        <apply>
          <divide/>
          <apply>
            <times/>
            <cn cellml:units="per_ms"> 0.095 </cn>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <minus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 5.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 100.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
          <apply>
            <plus/>
            <cn cellml:units="dimensionless"> 1.0 </cn>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <minus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 5.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 13.89 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>

    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="beta_d_calculation_eq">
      <apply id="beta_d_calculation">
        <eq/>
        <ci> beta_d </ci>
        <apply>
          <divide/>
          <apply>
            <times/>
            <cn cellml:units="per_ms"> 0.07 </cn>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <plus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 44.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 59.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
          <apply>
            <plus/>
            <cn cellml:units="dimensionless"> 1.0 </cn>
            <apply>
              <exp/>
              <apply>
                <divide/>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 44.0 </cn>
                </apply>
                <cn cellml:units="mV"> 20.0 </cn>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>

    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="dd_dt_eq">
      <apply id="dd_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> d </ci>
        </apply>
        <apply>
          <minus/>
          <apply>
            <times/>
            <ci> alpha_d </ci>
            <apply>
              <minus/>
              <cn cellml:units="dimensionless"> 1.0 </cn>
              <ci> d </ci>
            </apply>
          </apply>
          <apply>
            <times/>
            <ci> beta_d </ci>
            <ci> d </ci>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
  
  <!--
    The "slow_inward_current_f_gate" component is the f gate encapsulated in
    the slow inward current.
  -->
  <component name="slow_inward_current_f_gate" cmeta:id="slow_inward_current_f_gate">
    

    <!-- This variable is defined here and used in other components. -->
    <variable units="dimensionless" public_interface="out" cmeta:id="slow_inward_current_f_gate_f" name="f" initial_value="0.994"/> 

    <!-- These variables are defined here and only used internally. -->
    <variable units="per_ms" name="alpha_f" cmeta:id="slow_inward_current_f_gate_alpha_f"/>
    <variable units="per_ms" name="beta_f" cmeta:id="slow_inward_current_f_gate_beta_f"/>
    
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="mV" public_interface="in" name="V"/>
    <variable units="ms" public_interface="in" name="time"/>
     
     
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="alpha_f_calculation_eq">
      <!--
        The rate constants on the f gate are functions of membrane voltage.
      -->
      <apply id="alpha_f_calculation">
        <eq/>
        <ci> alpha_f </ci>
        <apply>
          <divide/>
          <apply>
            <times/>
            <cn cellml:units="per_ms"> 0.012 </cn>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <plus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 28.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 125.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
          <apply>
            <plus/>
            <cn cellml:units="dimensionless"> 1.0 </cn>
            <apply>
              <exp/>
              <apply>
                <divide/>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 28.0 </cn>
                </apply>
                <cn cellml:units="mV"> 6.67 </cn>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="beta_f_calculation_eq">
      <apply id="beta_f_calculation">
        <eq/>
        <ci> beta_f </ci>
        <apply>
          <divide/>
          <apply>
            <times/>
            <cn cellml:units="per_ms"> 0.0065 </cn>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <plus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 30.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 50.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
          <apply>
            <plus/>
            <cn cellml:units="dimensionless"> 1.0 </cn>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <plus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 30.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 5.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="df_dt_eq">
      <apply id="df_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> f </ci>
        </apply>
        <apply>
          <minus/>
          <apply>
            <times/>
            <ci> alpha_f </ci>
             <apply>
              <minus/>
              <cn cellml:units="dimensionless"> 1.0 </cn>
              <ci> f </ci>
            </apply>
          </apply>
          <apply>
            <times/>
            <ci> beta_f </ci>
            <ci> f </ci>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
    
  <!--  
    The "time_dependent_outward_current" component contains the                 
    differential equations governing the voltage- and time-dependent outward    
    current.  This current is predominately carried by potassium ions and it    
    is involved in the plateau of the action potential and in the               
    re-polarisation phase.  
  -->
    
  <component name="time_dependent_outward_current" cmeta:id="time_dependent_outward_current">
    

    <!-- This variable is defined here and used in other components. -->
    <variable units="uA_per_mm2" public_interface="out" name="i_x1" cmeta:id="time_dependent_outward_current_i_x1"/>
    
    <!-- These variables are imported from parent and sibling components. -->
    <variable units="ms" public_interface="in" private_interface="out" name="time"/>
    <variable units="mV" public_interface="in" private_interface="out" name="V"/>
     
    <!-- This variable is imported from encapsulated components. -->   
    <variable units="dimensionless" private_interface="in" name="x1"/>
        
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="i_x1_calculation_eq">
      <!--   
        The following equation calculates the time-dependent outward current    
        in terms of the membrane voltage. 
      -->
      <apply id="i_x1_calculation">
        <eq/>
        <ci> i_x1 </ci>
        <apply>
          <times/>
          <ci> x1 </ci>
          <cn cellml:units="dimensionless"> 8.0e-3 </cn>
          <apply>
            <divide/>
            <apply>
              <minus/>
              <apply>
                <exp/>
                <apply>
                  <times/>
                  <cn cellml:units="per_mV"> 0.04 </cn>
                  <apply>
                    <plus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 77.0 </cn>
                  </apply>
                </apply>
              </apply>
              <cn cellml:units="dimensionless"> 1.0 </cn>
            </apply>
            <apply>
              <exp/>
              <apply>
                <times/>
                <cn cellml:units="per_mV"> 0.04 </cn>
                <apply>
                  <plus/> 
                  <ci> V </ci>
                  <cn cellml:units="mV"> 35.0 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
  
  <component name="time_dependent_outward_current_x1_gate" cmeta:id="time_dependent_outward_current_x1_gate">
    

    <variable units="dimensionless" public_interface="out" name="x1" cmeta:id="time_dependent_outward_current_x1_gate_x1"/>
    <variable units="per_ms" name="alpha_x1" cmeta:id="time_dependent_outward_current_x1_gate_alpha_x1"/>
    <variable units="per_ms" name="beta_x1" cmeta:id="time_dependent_outward_current_x1_gate_beta_x1"/>
    <variable units="mV" public_interface="in" name="V"/>
    <variable units="ms" public_interface="in" name="time"/>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="alpha_x1_calculation_eq">
      <apply id="alpha_x1_calculation">
        <eq/>
        <ci> alpha_x1 </ci>
        <apply>
          <times/>
          <cn cellml:units="per_ms"> 5e-4 </cn>
          <apply>
            <divide/>
            <apply>
              <exp/>
              <apply>
                <divide/>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 50.0 </cn>                      
                </apply>
                <cn cellml:units="mV"> 12.1 </cn>
              </apply>
            </apply>
            <apply>
              <plus/>
              <cn cellml:units="dimensionless"> 1.0 </cn>
              <apply>
                <exp/>
                <apply>
                  <divide/>
                  <apply>
                    <plus/>
                    <ci> V </ci>
                    <cn cellml:units="mV"> 50.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 17.5 </cn>
                </apply>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="beta_x1_calculation_eq">
      <apply id="beta_x1_calculation">
        <eq/>
        <ci> beta_x1 </ci>
        <apply>
          <times/>
          <cn cellml:units="per_ms"> 0.0013 </cn>
          <apply>
            <divide/>
            <apply>
              <exp/>
              <apply>
                <minus/>
                <apply>
                  <divide/>
                  <apply>
                    <plus/>
                    <ci> V </ci>                                                
                    <cn cellml:units="mV"> 20.0 </cn>
                  </apply>
                  <cn cellml:units="mV"> 16.67 </cn>
                </apply>
              </apply>
            </apply>
            <apply>
              <plus/>
              <cn cellml:units="dimensionless"> 1.0 </cn>
              <apply>
                <exp/>
                <apply>
                  <minus/>
                  <apply>
                    <divide/>
                    <apply>
                      <plus/>
                      <ci> V </ci>
                      <cn cellml:units="mV"> 20.0 </cn>
                    </apply>
                    <cn cellml:units="mV"> 25.0 </cn>
                  </apply> 
                </apply>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
    
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="dx1_dt_eq">
      <apply id="dx1_dt">
        <eq/>
        <apply>
          <diff/>
          <bvar>
            <ci> time </ci>
          </bvar>
          <ci> x1 </ci>
        </apply>
        <apply>
          <minus/>
          <apply>
            <times/>
            <ci> alpha_x1 </ci>
            <apply>
              <minus/>
              <cn cellml:units="per_mV"> 1.0 </cn>
              <ci> x1 </ci>
            </apply>
          </apply>
          <apply>
            <times/>
            <ci> beta_x1 </ci>
            <ci> x1 </ci>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
     
  <!--  
    The "time_independent_outward_current" component contains the               
    equations governing the voltage-dependent, time-independent                 
    outward current.  This current is carried by potassium ions and it is       
    involved in the plateau of the action potential and in the                  
    re-polarisation phase.  Because the current is time-independent, it         
    can also be described as a background current.  
   -->
     
  <component name="time_independent_outward_current" cmeta:id="time_independent_outward_current">
    

    <!-- This variable is defined here and used in other components. -->
    <variable units="uA_per_mm2" public_interface="out" name="i_K1" cmeta:id="time_independent_outward_current_i_K1"/>
    
    <!-- These variables are imported from other components. -->
    <variable units="ms" public_interface="in" name="time"/>
    <variable units="mV" public_interface="in" name="V"/>
        
    <!--  
      The following equation calculates the time-independent outward            
      potassium current in terms of membrane voltage.  
    -->
    
    <math xmlns="http://www.w3.org/1998/Math/MathML" cmeta:id="i_K1_calculation_eq">
      <apply id="i_K1_calculation">
        <eq/>
        <ci> i_K1 </ci>
        <apply>
          <times/>
          <cn cellml:units="dimensionless"> 0.0035 </cn>
          <apply>
            <plus/>
            <apply>
              <times/>
              <cn cellml:units="per_ms"> 4.0 </cn>
              <apply>
                <divide/>
                <apply>
                  <minus/>
                  <apply>
                    <exp/>
                    <apply>
                      <times/>
                      <cn cellml:units="per_mV"> 0.04 </cn>
                      <apply>
                        <plus/>
                        <ci> V </ci>
                        <cn cellml:units="mV"> 85.0 </cn>
                      </apply>
                    </apply>                   
                  </apply>
                  <cn cellml:units="dimensionless"> 1.0 </cn>
                </apply>
                <apply>
                  <plus/>
                  <apply>
                    <exp/>
                    <apply>
                      <times/>
                      <cn cellml:units="per_mV"> 0.08 </cn>
                      <apply>
                        <plus/>
                        <ci> V </ci>
                        <cn cellml:units="mV"> 53 </cn>
                      </apply>
                    </apply>
                  </apply>
                  <apply>
                    <exp/>
                    <apply>
                      <times/> 
                      <cn cellml:units="per_mV"> 0.04 </cn>
                      <apply>
                        <plus/>
                        <ci> V </ci>
                        <cn cellml:units="mV"> 53.0 </cn>
                      </apply>
                    </apply>          
                  </apply>
                </apply>
              </apply>
            </apply>
            <apply>
              <times/>
              <cn cellml:units="per_ms"> 0.2 </cn>
              <apply>
                <divide/>
                <apply>
                  <plus/>
                  <ci> V </ci>
                  <cn cellml:units="mV"> 23.0 </cn>
                </apply>
                <apply>
                  <minus/>
                  <cn cellml:units="dimensionless"> 1.0 </cn>
                  <apply>
                    <exp/>
                    <apply>
                      <times/>
                      <cn cellml:units="per_mV"> -0.04 </cn>
                      <apply>
                        <plus/>
                        <ci> V </ci>
                        <cn cellml:units="mV"> 23.0 </cn>
                      </apply>
                    </apply>
                  </apply>
                </apply>
              </apply>
            </apply>
          </apply>
        </apply>
      </apply>
    </math>
  </component>
   
  <!--
    The following <group> element specifies a single containment hierarchy
    that encompasses all of the components in the model, with the exception of
    the "environment" component.
  -->
  <group>
    <relationship_ref relationship="containment"/>
    <component_ref component="membrane">
      <component_ref component="sodium_current">
        <component_ref component="sodium_current_m_gate"/>
        <component_ref component="sodium_current_h_gate"/>
        <component_ref component="sodium_current_j_gate"/>
      </component_ref>
      <component_ref component="slow_inward_current">
        <component_ref component="slow_inward_current_d_gate"/>
        <component_ref component="slow_inward_current_f_gate"/>
      </component_ref>
      <component_ref component="time_dependent_outward_current">
        <component_ref component="time_dependent_outward_current_x1_gate"/>
      </component_ref>
      <component_ref component="time_independent_outward_current"/>
    </component_ref>
  </group>


  <!--
    The following <group> element specifies how the components representing
    activation and inactivation coefficients are encapsulated inside the
    sodium and potassium channel components.  
  -->
  <group>
    <relationship_ref relationship="encapsulation"/>
    <component_ref component="sodium_current">
      <component_ref component="sodium_current_m_gate"/>
      <component_ref component="sodium_current_h_gate"/>
      <component_ref component="sodium_current_j_gate"/>
    </component_ref>
    <component_ref component="slow_inward_current">
      <component_ref component="slow_inward_current_d_gate"/>
      <component_ref component="slow_inward_current_f_gate"/>
    </component_ref>
    <component_ref component="time_dependent_outward_current">
      <component_ref component="time_dependent_outward_current_x1_gate"/>
    </component_ref>
  </group>
  
<!--
  The connections hold the actual mappings between variables declared in
  different components. When more than one variable is mapped between two
  components, all variable mappings must be listed in the same connection
  element (there can only be one connection between two components). The
  variables are assumed to be listed in the same order within the two
  <component_ref> elements. The modeler should NOT rely on matching the
  names of the variables in the two components.
-->

  <!--
    "time" is passed from the "environment" component into the
    "membrane" and current components.
  -->
  <connection>
    <map_components component_2="environment" component_1="membrane"/>
    <map_variables variable_2="time" variable_1="time"/>
  </connection>

  <connection>
    <map_components component_2="environment" component_1="sodium_current"/>
    <map_variables variable_2="time" variable_1="time"/>
  </connection>

  <connection>
    <map_components component_2="environment" component_1="slow_inward_current"/>
    <map_variables variable_2="time" variable_1="time"/>
  </connection>

  <connection>
    <map_components component_2="environment" component_1="time_dependent_outward_current"/>
    <map_variables variable_2="time" variable_1="time"/>
  </connection>
   
  <connection>
    <map_components component_2="environment" component_1="time_independent_outward_current"/>
    <map_variables variable_2="time" variable_1="time"/>
  </connection>
  
  <!--
    A number of variables are passed between the "membrane" and its four
    sub-components, the "sodium_current", "slow_inward_current",                
    "time_dependent_outward_current" and the "time_independent_outward_current".
  -->
  <connection>
    <map_components component_2="sodium_current" component_1="membrane"/>
    <map_variables variable_2="V" variable_1="V"/>
     <map_variables variable_2="i_Na" variable_1="i_Na"/>
  </connection>

  <connection>
    <map_components component_2="slow_inward_current" component_1="membrane"/>
    <map_variables variable_2="V" variable_1="V"/>
    <map_variables variable_2="i_s" variable_1="i_s"/>
  </connection>

  <connection>
    <map_components component_2="time_dependent_outward_current" component_1="membrane"/>
    <map_variables variable_2="V" variable_1="V"/>
    <map_variables variable_2="i_x1" variable_1="i_x1"/>
  </connection>
  
  <connection>
    <map_components component_2="time_independent_outward_current" component_1="membrane"/>
    <map_variables variable_2="V" variable_1="V"/>
    <map_variables variable_2="i_K1" variable_1="i_K1"/>
  </connection>
   
   <!--
    Various gating variables are passed between the "sodium_current" and
    "slow_inward_current" components and the encapsulated "beeler_reuter_gate"
    components.
  -->
  <connection>
    <map_components component_2="sodium_current_m_gate" component_1="sodium_current"/>
    <map_variables variable_2="m" variable_1="m"/>
    <map_variables variable_2="time" variable_1="time"/>
    <map_variables variable_2="V" variable_1="V"/>
  </connection>

  <connection>
    <map_components component_2="sodium_current_h_gate" component_1="sodium_current"/>
    <map_variables variable_2="h" variable_1="h"/>
    <map_variables variable_2="time" variable_1="time"/>
    <map_variables variable_2="V" variable_1="V"/>
  </connection>
 
  <connection>
    <map_components component_2="sodium_current_j_gate" component_1="sodium_current"/>
    <map_variables variable_2="j" variable_1="j"/>
    <map_variables variable_2="time" variable_1="time"/>
    <map_variables variable_2="V" variable_1="V"/>
  </connection>
  
  <connection>
    <map_components component_2="time_dependent_outward_current_x1_gate" component_1="time_dependent_outward_current"/>
    <map_variables variable_2="x1" variable_1="x1"/>
    <map_variables variable_2="time" variable_1="time"/>
    <map_variables variable_2="V" variable_1="V"/>
  </connection>
  
  <connection>
    <map_components component_2="slow_inward_current_d_gate" component_1="slow_inward_current"/>
    <map_variables variable_2="d" variable_1="d"/>
    <map_variables variable_2="time" variable_1="time"/>
    <map_variables variable_2="V" variable_1="V"/>
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  <connection>
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    <map_variables variable_2="V" variable_1="V"/>
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<component name="stimulus_protocol">
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    <variable units="ms" cmeta:id="stimulus_protocol_IstimEnd" name="IstimEnd" initial_value="50000"/>
    <variable units="uA_per_mm2" cmeta:id="stimulus_protocol_IstimAmplitude" name="IstimAmplitude" initial_value="0.5"/>
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    <variable units="ms" cmeta:id="stimulus_protocol_IstimPulseDuration" name="IstimPulseDuration" initial_value="1"/>
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              <apply>
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                    <ci>IstimPeriod</ci>
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              </apply>
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        </piecewise>
      </apply>
    </math>
    <variable units="ms" public_interface="in" name="time"/>
  </component>
  <connection>
    <map_components component_2="stimulus_protocol" component_1="membrane"/>
    <map_variables variable_2="Istim" variable_1="Istim"/>
  </connection>
  <connection>
    <map_components component_2="stimulus_protocol" component_1="environment"/>
    <map_variables variable_2="time" variable_1="time"/>
  </connection>
















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