The Simulation of Repolarization Events of the Cardiac Purkinje Fiber Action Potential

A mathematical model based on the formalism of the Hodgkin-Huxley equations was implemented on a microcomputer system and used to simulate the membrane action potential of cardiac Purkinje fibers. The complete model is a modification of the representation used by McAllister et al. [1], mainly with respect to the outward current components during the late plateau, the repolarization phase, and the slow repolarization phase of the action potential. A new formulation of the potassium conductance was used, involving two distinct types of ionic channels corresponding, respectively, to the experimentally observed inward-going and outward-going rectification properties of the Purkinje fiber membrane. A unified representation of the Purkinje fiber current components was thus obtained which provides a more satisfactory interpretation of experimental results than was possible with the original model of McAllister et al. [1]. The membrane channel for the potassium pacemaker current is characterized by a set of first-order activation-inactivation variables and a constant fully activated conductance. The other channel carries the potassium current involved in the late plateau and repolarization phase of the action potential.