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Over the past years significant results have been achieved in the mathematical modeling and computer simulation of action potential generation and propagation using Hodgkin-Huxley formalism. The development of the single channel clamp experiment technique has provided new experimental data, and also led to a Markovian formulation of the ion channels gating processes. The advantages of this formulation are: it makes the artificial Hodgkin-Huxley assumption of mutual independence of gating processes unnecessary and also opens the possibility of simulating the effects of drugs, toxins and genetic defects in channel proteins on the behavior of cardiac cells. The comparison of the effect of Markovian and Hodgkin-Huxley representations for major voltage dependent channels presented here shows that at normal pacing rates both representations give the same action potential shape without significant changes in its basic characteristics. For pacing rates encountered during heart tachycardia and fibrillation, we observe that the Markovian representations yield maximum sodium and rapid potassium currents that decrease much more than the corresponding currents in the cell model with the Hodgkin-Huxley formulation. The decrease of the sodium current reduces the depolarization rate and ultimately the velocity of wave propagation. The decrease of the rapid potassium current increases the duration of the action potential and causes early after depolarization in the presence of intracellular calcium accumulation and spontaneous sarcoplasmic reticulum ca2'release. Transactions on Biomedicine and Health vol 6, © 2003 WIT Press, www.witpress.com, ISSN 1743-3525

The cardiac cell model at normal and high pacing rates with Markovian representations of gating processes (Computer simulation study)