Location: Bertram, Arnot, Zamponi, 2002 @ 1f727f9df5fe / bertram_arnot_zamponi_2002.cellml

Author:
pmr2.import <nobody@models.cellml.org>
Date:
2006-07-09 07:21:53+12:00
Desc:
committing version01 of bertram_arnot_zamponi_2002
Permanent Source URI:
https://models.cellml.org/workspace/bertram_arnot_zamponi_2002/rawfile/1f727f9df5fe010424b5a8326545a3276a83e6ae/bertram_arnot_zamponi_2002.cellml

<?xml version='1.0' encoding='utf-8'?>
<!--  FILE :bertram_model_2002.xml

CREATED :  6th November 2002

LAST MODIFIED : 20th April 2005

AUTHOR :  Catherine Lloyd
          Bioengineering Institute
          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 Bertram, Arnot and Zamponi's 2002 analysis of the role of G Protein G-beta-gamma isoform specificity in synaptic signal processing.

CHANGES:  
  09/04/2003 - AAC - Added publication date information.  
  20/04/2005 - PJV - Made MathML id's unique
--><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#" cmeta:id="bertram_arnot_zamponi_2002_version01" name="bertram_arnot_zamponi_2002_version01">
<documentation xmlns="http://cellml.org/tmp-documentation">
<article>
  <articleinfo>
  <title>G-Protein Specificity In Synaptic Signalling</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 is the original unchecked version of the model imported from the previous
            CellML model repository, 24-Jan-2006.
          </para>
  </section>
  <sect1 id="sec_structure">
<title>Model Structure</title>

<para>
Ca<superscript>2+</superscript> flux through voltage-gated channels plays a role in muscle contraction, gene expression, synaptic transmission, short- and long-term memory.  Ca<superscript>2+</superscript> channels are regulated by many electrical, genetic and biochemical pathways, including G-protein signal transduction pathways.  In their 2002 study, Richard Bertram, Michelle I. Arnot, and Gerald W. Zamponi focus on the direct regulation of N-type Ca<superscript>2+</superscript> channels by the G-beta-gamma subunits of activated G-proteins (see <xref linkend="fig_reaction_diagram"/> below).  Ca<superscript>2+</superscript> ion binding to a low-affinity binding site induces vesicle fusion with the plasma membrane, followed by the release of transmitter by exocytosis.  Transmitter binding to a presynaptic autoreceptor activates a G-protein, the G-beta-gamma subunit od which binds directly to an N-type Ca<superscript>2+</superscript> channel.  Such binding puts channels into a reluctant state, reducing the net flow of Ca<superscript>2+</superscript> into the cell.  Autoinhibition of transmitter release then occurs as the result of the G-protein-mediated inhibition of Ca<superscript>2+</superscript> channels.  The resultant depolarisation results in the unbinding of G-beta-gamma from the channel. 
</para>

<para>
The mathematical model developed by bertram <emphasis>et al.</emphasis> in this study was used to address two questions: 1) What is the role of G-protein-mediated autoinhibition on synaptic signalling processing; and 2) How is signal processing affected by different G-beta-gamma isoforms?  The presynaptic model has equations for membrane potential, Ca<superscript>2+</superscript>-dependent transmitter release, transmitter binding to autoreceptors, and Ca<superscript>2+</superscript> influx through G-protein-regulated channels.  This mathematical model has been translated into a CellML description which can be downloaded in various formats as described in <xref linkend="sec_download_this_model"/>.
</para>

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

<para>
<ulink url="http://jn.physiology.org/cgi/content/abstract/87/5/2612">Role for G Protein G-Beta-Gamma Isoform Specificity in Synaptic Signal Processing: A Computational Study</ulink>, Richard Bertram, Michelle I. Arnot, and Gerald W. Zamponi, 2002, <ulink url="http://jn.physiology.org/">
            <emphasis>Journal of Neurophysiology</emphasis>
          </ulink>, 87, 2612-2623.  (<ulink url="http://jn.physiology.org/cgi/content/full/87/5/2612">Full text</ulink> and <ulink url="http://jn.physiology.org/cgi/reprint/87/5/2612.pdf">PDF</ulink> versions of the article are available for Journal Members on the Journal of Neurophysiology website.)  <ulink url="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&amp;db=PubMed&amp;list_uids=11976397&amp;dopt=Abstract">PubMed ID: 11976397</ulink>  
</para>


<informalfigure float="0" id="fig_reaction_diagram">
<mediaobject>
  <imageobject>
    <objectinfo>
      <title>reaction diagram</title>
    </objectinfo>
    <imagedata fileref="reaction_diagram.gif"/>
  </imageobject>
</mediaobject>
<caption>Schematic diagram of the presynaptic model.</caption>
</informalfigure>

<para>
G-protein autoinhibitory feedback on the presynaptic terminal acts like a high-pass filter, allowing only high-frequency signals to pass through the to the postsynaptic cell.  Low-frequency signals are effectively filtered out.  Model simulations in this study show how different G-beta-gamma isoforms have different filtering properties.  They also emphasise that the different filtering characteristics associated with a specific G-beta-gamma subunit depend on many biophysical parameters, such as the unbinding rate of a transmitter molecule from the presynaptic autoreceptor.  For example faster unbinding lowers the filter cut while slower unbinding raises it.  This allows for great synapse-tot-synapse variability in the distinction between signal and background noise.
</para>

</sect1>
</article>
</documentation>
  
    
  <!--
    Below, we define some additional units for association with variables and
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  -->
  
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      <unit units="kelvin" exponent="-1"/>
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   <units name="coulomb_per_mole">
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      <unit units="mole" exponent="-1"/>
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  <!--
    The "environment" component is used to declare variables that are used by
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  -->
   
   <component name="environment">
      <variable units="millisecond" public_interface="out" name="time"/>
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   <!--
    The presynaptic terminal is modelled with equations for membrane potential, Ca2+-dependent transmitter release, transmitter binding to autoreceptors and Ca2+ influx through G protein-regulated channels.
  -->
  
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      </apply>
    </math>
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  <component name="leak_current">
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   <!--
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            <eq/>
            <apply>
               <diff/>
               <bvar>
                  <ci>time</ci>
               </bvar>
               <ci>C_G1</ci>
            </apply>
            <apply>
               <plus/>
               <ci>delta_C_G1_rxn6</ci>
               <ci>delta_C_G1_rxn4</ci>
            </apply>
         </apply>
      </math>
   </component>
  
   <component cmeta:id="C_G2" name="C_G2">
      <variable units="micromolar" public_interface="out" name="C_G2" initial_value="1.0"/>
      <variable units="flux" public_interface="in" name="delta_C_G2_rxn4"/>
      <variable units="flux" public_interface="in" name="delta_C_G2_rxn7"/>
      <variable units="flux" public_interface="in" name="delta_C_G2_rxn5"/>
      <variable units="millisecond" public_interface="in" name="time"/>
      <math xmlns="http://www.w3.org/1998/Math/MathML">
         <apply>
            <eq/>
            <apply>
               <diff/>
               <bvar>
                  <ci>time</ci>
               </bvar>
               <ci>C_G2</ci>
            </apply>
            <apply>
               <plus/>
               <ci>delta_C_G2_rxn4</ci>
               <ci>delta_C_G2_rxn7</ci>
               <ci>delta_C_G2_rxn5</ci>
            </apply>
         </apply>
      </math>
   </component>
   
   <component cmeta:id="C_G3" name="C_G3">
      <variable units="micromolar" public_interface="out" name="C_G3" initial_value="1.0"/>
      <variable units="flux" public_interface="in" name="delta_C_G3_rxn5"/>
      <variable units="flux" public_interface="in" name="delta_C_G3_rxn8"/>
      <variable units="millisecond" public_interface="in" name="time"/>
      <math xmlns="http://www.w3.org/1998/Math/MathML">
         <apply>
            <eq/>
            <apply>
               <diff/>
               <bvar>
                  <ci>time</ci>
               </bvar>
               <ci>C_G3</ci>
            </apply>
            <apply>
               <plus/>
               <ci>delta_C_G3_rxn5</ci>
               <ci>delta_C_G3_rxn8</ci>
            </apply>
         </apply>
      </math>
   </component>
   
   <!--
    The following components describe the kinetics and reactions of the model.
   -->
   
   <component name="rate_constants">
     <variable units="first_order_rate_constant" public_interface="out" name="alpha"/>
     <variable units="first_order_rate_constant" public_interface="out" name="alpha_"/>
     <variable units="first_order_rate_constant" public_interface="out" name="beta"/>
     <variable units="first_order_rate_constant" public_interface="out" name="beta_"/>
     <variable units="first_order_rate_constant" public_interface="out" name="kG_plus"/>
     
     <variable units="dimensionless" name="a"/>
     <variable units="second_order_rate_constant" name="ka_plus" initial_value="200.0"/>
     <variable units="first_order_rate_constant" name="ka_minus" initial_value="0.0015"/>
     <variable units="millimolar" name="T" initial_value="1.0"/>
     
     <variable units="millivolt" public_interface="in" name="V"/>
     <variable units="millisecond" public_interface="in" name="time"/>
     
     <math xmlns="http://www.w3.org/1998/Math/MathML">
       <apply id="rate_constants_alpha_calculation">
        <eq/>
         <ci> alpha </ci>
         <apply>
          <times/>
           <cn cellml:units="first_order_rate_constant"> 0.45 </cn>
           <apply>
            <exp/>
             <apply>
              <divide/>
               <ci> V </ci>
               <cn cellml:units="millivolt"> 22.0 </cn>
             </apply>
           </apply>
         </apply>
       </apply>
       
       <apply id="alpha_calculation">
        <eq/>
         <ci> alpha_ </ci>
         <apply>
          <divide/>
           <ci> alpha </ci>
           <cn cellml:units="dimensionless"> 8.0 </cn>
         </apply>
       </apply>
       
       <apply id="beta_calculation">
        <eq/>
         <ci> beta </ci>
         <apply>
          <times/>
           <cn cellml:units="first_order_rate_constant"> 0.015 </cn>
           <apply>
            <exp/>
             <apply>
              <divide/>
               <apply>
                <minus/>
                 <ci> V </ci>
               </apply>
               <cn cellml:units="millivolt"> 14.0 </cn>
             </apply>
           </apply>
         </apply>
       </apply>
       
       <apply id="alpha__calculation">
        <eq/>
         <ci> beta_ </ci>
         <apply>
          <times/>
           <ci> beta </ci>
           <cn cellml:units="dimensionless"> 8.0 </cn>
         </apply>
       </apply>
       
       <apply id="da_dt">
        <eq/>
         <apply>
          <diff/>
           <bvar>
            <ci> time </ci>
          </bvar>
           <ci> a </ci>
         </apply>
         <apply>
          <minus/>
           <apply>
            <times/>
             <ci> ka_plus </ci>
             <ci> T </ci>
             <apply>
              <minus/>
               <cn cellml:units="dimensionless"> 1.0 </cn>
               <ci> a </ci>
             </apply>
           </apply>
           <apply>
            <times/>
             <ci> ka_minus </ci>
             <ci> a </ci>
           </apply>
         </apply>
       </apply>
       
       <apply id="kG_plus_calculation">
        <eq/>
         <ci> kG_plus </ci>
         <apply>
          <divide/>
           <apply>
            <times/>
             <cn cellml:units="first_order_rate_constant"> 3.0 </cn>
             <ci> a </ci>
           </apply>
           <apply>
            <plus/>
             <cn cellml:units="dimensionless"> 680.0 </cn>
             <apply>
              <times/>
               <cn cellml:units="dimensionless"> 320.0 </cn>
               <ci> a </ci>
             </apply>
           </apply>
         </apply>
       </apply>
     </math>
   </component>
  
   <component name="reaction0">
      <variable units="micromolar" public_interface="in" name="C1"/>
      <variable units="micromolar" public_interface="in" name="C2"/>
      <variable units="flux" public_interface="out" name="delta_C1_rxn0"/>
      <variable units="flux" public_interface="out" name="delta_C2_rxn0"/>
      <variable units="first_order_rate_constant" public_interface="in" name="alpha"/>
      <variable units="first_order_rate_constant" public_interface="in" name="beta"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C1">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C1_rxn0" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C2">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C2_rxn0" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <cn cellml:units="dimensionless"> 4.0 </cn>
                           <ci>alpha</ci>
                           <ci>C1</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <ci>beta</ci>
                              <ci>C2</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
   
   <component name="reaction1">
      <variable units="micromolar" public_interface="in" name="C2"/>
      <variable units="micromolar" public_interface="in" name="C3"/>
      <variable units="flux" public_interface="out" name="delta_C2_rxn1"/>
      <variable units="flux" public_interface="out" name="delta_C3_rxn1"/>
      <variable units="first_order_rate_constant" public_interface="in" name="alpha"/>
      <variable units="first_order_rate_constant" public_interface="in" name="beta"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C2">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C2_rxn1" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C3">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C3_rxn1" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <cn cellml:units="dimensionless"> 3.0 </cn>
                           <ci>alpha</ci>
                           <ci>C2</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <cn cellml:units="dimensionless"> 2.0 </cn>
                              <ci>beta</ci>
                              <ci>C3</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
   
   <component name="reaction2">
      <variable units="micromolar" public_interface="in" name="C3"/>
      <variable units="micromolar" public_interface="in" name="C4"/>
      <variable units="flux" public_interface="out" name="delta_C3_rxn2"/>
      <variable units="flux" public_interface="out" name="delta_C4_rxn2"/>
      <variable units="first_order_rate_constant" public_interface="in" name="alpha"/>
      <variable units="first_order_rate_constant" public_interface="in" name="beta"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C3">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C3_rxn2" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C4">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C4_rxn2" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <cn cellml:units="dimensionless"> 2.0 </cn>
                           <ci>alpha</ci>
                           <ci>C3</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <cn cellml:units="dimensionless"> 3.0 </cn>
                              <ci>beta</ci>
                              <ci>C4</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
  
   <component name="reaction3">
      <variable units="micromolar" public_interface="in" name="C4"/>
      <variable units="micromolar" public_interface="in" name="O"/>
      <variable units="flux" public_interface="out" name="delta_C4_rxn3"/>
      <variable units="flux" public_interface="out" name="delta_O_rxn3"/>
      <variable units="first_order_rate_constant" public_interface="in" name="alpha"/>
      <variable units="first_order_rate_constant" public_interface="in" name="beta"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C4">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C4_rxn3" role="reactant"/>
         </variable_ref>
         <variable_ref variable="O">
            <role stoichiometry="1" direction="forward" delta_variable="delta_O_rxn3" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <ci>alpha</ci>
                           <ci>C4</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <cn cellml:units="dimensionless"> 4.0 </cn>
                              <ci>beta</ci>
                              <ci>O</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
  
   <component name="reaction4">
      <variable units="micromolar" public_interface="in" name="C_G1"/>
      <variable units="micromolar" public_interface="in" name="C_G2"/>
      <variable units="flux" public_interface="out" name="delta_C_G1_rxn4"/>
      <variable units="flux" public_interface="out" name="delta_C_G2_rxn4"/>
      <variable units="first_order_rate_constant" public_interface="in" name="alpha_"/>
      <variable units="first_order_rate_constant" public_interface="in" name="beta_"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C_G1">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G1_rxn4" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C_G2">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G2_rxn4" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <cn cellml:units="dimensionless"> 4.0 </cn>
                           <ci>alpha_</ci>
                           <ci>C_G1</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <ci>beta_</ci>
                              <ci>C_G2</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
  
   <component name="reaction5">
      <variable units="micromolar" public_interface="in" name="C_G2"/>
      <variable units="micromolar" public_interface="in" name="C_G3"/>
      <variable units="flux" public_interface="out" name="delta_C_G2_rxn5"/>
      <variable units="flux" public_interface="out" name="delta_C_G3_rxn5"/>
      <variable units="first_order_rate_constant" public_interface="in" name="alpha_"/>
      <variable units="first_order_rate_constant" public_interface="in" name="beta_"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C_G2">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G2_rxn5" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C_G3">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G3_rxn5" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <cn cellml:units="dimensionless"> 3.0 </cn>
                           <ci>alpha_</ci>
                           <ci>C_G2</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <cn cellml:units="dimensionless"> 2.0 </cn>
                              <ci>beta_</ci>
                              <ci>C_G3</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
   
   <component name="reaction6">
      <variable units="micromolar" public_interface="in" name="C1"/>
      <variable units="micromolar" public_interface="in" name="C_G1"/>
      <variable units="flux" public_interface="out" name="delta_C1_rxn6"/>
      <variable units="flux" public_interface="out" name="delta_C_G1_rxn6"/>
      <variable units="first_order_rate_constant" public_interface="in" name="kG_plus"/>
      <variable units="first_order_rate_constant" name="kG_minus" initial_value="0.00025"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C1">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C1_rxn6" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C_G1">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G1_rxn6" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <ci>kG_plus</ci>
                           <ci>C1</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <ci>kG_minus</ci>
                              <ci>C_G1</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
   
   <component name="reaction7">
      <variable units="micromolar" public_interface="in" name="C2"/>
      <variable units="micromolar" public_interface="in" name="C_G2"/>
      <variable units="flux" public_interface="out" name="delta_C2_rxn7"/>
      <variable units="flux" public_interface="out" name="delta_C_G2_rxn7"/>
      <variable units="first_order_rate_constant" public_interface="in" name="kG_plus"/>
      <variable units="first_order_rate_constant" name="kG2_minus" initial_value="0.01"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C2">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C2_rxn7" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C_G2">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G2_rxn7" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <ci>kG_plus</ci>
                           <ci>C2</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <ci>kG2_minus</ci>
                              <ci>C_G2</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
   
   <component name="reaction8">
      <variable units="micromolar" public_interface="in" name="C3"/>
      <variable units="micromolar" public_interface="in" name="C_G3"/>
      <variable units="flux" public_interface="out" name="delta_C3_rxn8"/>
      <variable units="flux" public_interface="out" name="delta_C_G3_rxn8"/>
      <variable units="first_order_rate_constant" public_interface="in" name="kG_plus"/>
      <variable units="first_order_rate_constant" name="kG3_minus" initial_value="0.0005"/>
      <variable units="flux" name="rate"/>
      <reaction reversible="yes">
         <variable_ref variable="C3">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C3_rxn8" role="reactant"/>
         </variable_ref>
         <variable_ref variable="C_G3">
            <role stoichiometry="1" direction="forward" delta_variable="delta_C_G3_rxn8" role="product"/>
         </variable_ref>
         <variable_ref variable="rate">
            <role role="rate">
               <math xmlns="http://www.w3.org/1998/Math/MathML">
                  <apply>
                     <eq/>
                     <ci>rate</ci>
                     <apply>
                        <plus/>
                        <apply>
                           <times/>
                           <ci>kG_plus</ci>
                           <ci>C3</ci>
                        </apply>
                        <apply>
                           <minus/>
                           <apply>
                              <times/>
                              <ci>kG3_minus</ci>
                              <ci>C_G3</ci>
                           </apply>
                        </apply>
                     </apply>
                  </apply>
               </math>
            </role>
         </variable_ref>
      </reaction>
   </component>
   
   <group>
    <relationship_ref relationship="encapsulation"/>
    <component_ref component="potassium_current">
      <component_ref component="potassium_current_n_gate"/>
    </component_ref>
  </group>
   
   <connection>
      <map_components component_2="reaction0" component_1="C1"/>
      <map_variables variable_2="C1" variable_1="C1"/>
      <map_variables variable_2="delta_C1_rxn0" variable_1="delta_C1_rxn0"/>
   </connection>
  
   <connection>
      <map_components component_2="reaction6" component_1="C1"/>
      <map_variables variable_2="C1" variable_1="C1"/>
      <map_variables variable_2="delta_C1_rxn6" variable_1="delta_C1_rxn6"/>
   </connection>
  
   <connection>
      <map_components component_2="reaction0" component_1="C2"/>
      <map_variables variable_2="C2" variable_1="C2"/>
      <map_variables variable_2="delta_C2_rxn0" variable_1="delta_C2_rxn0"/>
   </connection>
  
   <connection>
      <map_components component_2="reaction1" component_1="C2"/>
      <map_variables variable_2="C2" variable_1="C2"/>
      <map_variables variable_2="delta_C2_rxn1" variable_1="delta_C2_rxn1"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction7" component_1="C2"/>
      <map_variables variable_2="C2" variable_1="C2"/>
      <map_variables variable_2="delta_C2_rxn7" variable_1="delta_C2_rxn7"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction1" component_1="C3"/>
      <map_variables variable_2="C3" variable_1="C3"/>
      <map_variables variable_2="delta_C3_rxn1" variable_1="delta_C3_rxn1"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction2" component_1="C3"/>
      <map_variables variable_2="C3" variable_1="C3"/>
      <map_variables variable_2="delta_C3_rxn2" variable_1="delta_C3_rxn2"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction8" component_1="C3"/>
      <map_variables variable_2="C3" variable_1="C3"/>
      <map_variables variable_2="delta_C3_rxn8" variable_1="delta_C3_rxn8"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction2" component_1="C4"/>
      <map_variables variable_2="C4" variable_1="C4"/>
      <map_variables variable_2="delta_C4_rxn2" variable_1="delta_C4_rxn2"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction3" component_1="C4"/>
      <map_variables variable_2="C4" variable_1="C4"/>
      <map_variables variable_2="delta_C4_rxn3" variable_1="delta_C4_rxn3"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction3" component_1="O"/>
      <map_variables variable_2="O" variable_1="O"/>
      <map_variables variable_2="delta_O_rxn3" variable_1="delta_O_rxn3"/>
   </connection>
  
   <connection>
      <map_components component_2="reaction6" component_1="C_G1"/>
      <map_variables variable_2="C_G1" variable_1="C_G1"/>
      <map_variables variable_2="delta_C_G1_rxn6" variable_1="delta_C_G1_rxn6"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction4" component_1="C_G1"/>
      <map_variables variable_2="C_G1" variable_1="C_G1"/>
      <map_variables variable_2="delta_C_G1_rxn4" variable_1="delta_C_G1_rxn4"/>
   </connection>
   
   <connection>
      <map_components component_2="reaction4" component_1="C_G2"/>
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