Computer simulation of acidosis-induced abnormal repolarization and repetitive activity in dog Purkinje fibers

Equations described by Mc Allister et al. (1975) were used to simulate the abnormal repolarization phase of the action potential (early after depolarization or hump), which often occurs in isolated dog Purkinje fibers submitted to acid media and can result in re-excitation. The development of humps was simulated by modifying the īK2-Em relationship in such a way that the resulting repolarizing current was increased at low membrane potential and decreased at higher (more negative) membrane potential. Beyond a certain size, humps triggered single, or multiple re-excitations. Hump size was very sensitive to small changes in īK2 and iK1, moderately sensitive to changes in īx1 and almost insensitive to changes in ix2. Negative shifts in the s infinity-Em relationship induced slowing of the basic frequency and only a small decrease in hump size. Decreasing gsi and gNa exerted inhibitory effects on hump development, the latter effect being larger than the former. The steady-state inward sodium current resulting from the overlap of m infinity-Em and h infinity-Em relationships appeared of particular importance in the development of humps.