Reconstruction of the electrical activity of cardiac Purkinje fibres.

Model Status

This is a code and units checked version of the model including two variants - A and B - with different formulations for the transient chloride current r gate. The kinetics for this gate in Model B come from an extensive study by Fozzard and Hiraoka. Results using model A are very dependent on initial conditions. Model B has a notch which is less frequency labile than that of model A. This is model A.

Model Structure

Following Denis Noble's 1962 model of cardiac action potentials in Purkinje fibres, the next significant development in cardiac membrane modelling occurred when R.E. McAllister, D. Noble and R.W. Tsien (1975) published a paper which formulated new ionic current equations based on new experimental data. The description of the kinetics of the currents is still based on the Hodgkin-Huxley formalism, but the currents themselves incorporate some significant new changes, and the total ionic current is broken down into nine discrete, individual ionic fluxes (see the figure below).

The complete original paper reference is cited below:

Reconstruction of the Electrical Activity of Cardiac Purkinje Fibres, McAllister, R.E. Noble, D. and Tsien, R.W. 1975, Journal of Physiology , 251, 1-59. PubMed ID: 1185607

A schematic diagram describing the current flows across the cell membrane that are captured in the MNT model.

The network defined in the CellML description of the McAllister-Noble-Tsien model. A key describing the significance of the shapes of the components and the colours of the connections between them is in the notation guide. For simplicity, not all the variables are shown.

The membrane physically contains the currents as indicated by the blue arrows in . The currents act independently and are not connected to each other. Several of the channels encapsulate and 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.

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.