Reconstruction of the action potential of ventricular myocardial fibres

Abstract

A mathematical model of membrane action potentials of mammalian ventricular myocardial fibers is described. The reconstruction model is based as closely as possible on ionic currents which were measured by the voltage-clamp method. Four individual components of ionic current were formulated mathematically in terms of Hodgkin-Huxley type equations. The model incorporates 2 voltage- and time-dependent inward currents, the excitatory inward Na current, iNa, and a secondary or slow inward current, is, primarily carried by Ca ions. A time-independent outward K current, iK1, exhibiting inward-going rectification and a voltage- and time-dependent outward current, ix1, primarily carried by K ions, are further elements of the model. The iNa is primarily responsible for the rapid upstroke of the action potential, while the other current components determine the configuration of the plateau of the action potential and the re-polarization phase. The relative importance of inactivation of is and of activation of ix1 for termination of the plateau is evaluated by the model. Experimental phenomena like slow recovery of the Na system from inactivation, frequency dependence of the action potential duration, all-or-nothing re-polarization and membrane oscillations are adequately described by the model. Possible inadequacies and shortcomings of the model are discussed.