A dynamic action potential model analysis of shock-induced aftereffects in ventricular muscle by reversible breakdown of cell membrane

To elucidate the subcellular mechanism underlying the aftereffects of high-intensity dc shocks, a small pore, which mimics reversible breakdown of the cell membrane (electroporation), was incorporated into the phase-2 Luo-Rudy (L-R) model of ventricular action potentials. The pore size was set to occupy 0.15%-0.25% of the total cell membrane during the 10-ms shock. The pore was assumed to decrease after the shock exponentially with a time constant of 100-1400 ms to simulate resealing process. In normal myocytes, the pore formation results in a delay of repolarization of the shocked action potential, which is followed by prolonged depolarization and oscillation of membrane potential like early afterdepolarization (EAD). Time- and voltage-dependent changes in the delayed rectifier K ⁺ currents (I _Kr, I _Ks) in combination with those of L-type Ca ²⁺ current (I _Ca, _(L)) and ion flux through the pore (I _pore) are responsible for the potential changes. Spontaneous excitation from the oscillation depends on activation of I _{Ca, (L)}. In myocytes overloaded with Na ⁺ and Ca ²⁺ secondary to 90% inhibition of Na ⁺-K ⁺ pump, the pore formation results in a delay of repolarization of the shocked action potential, which is followed by slower cyclic depolarization in response to spontaneous release of Ca ²⁺ from the sarcoplasmic reticulum (SR). This delayed after depolarization-type oscillation is abolished by complete block of Ca ²⁺ release from the SR. These findings suggest that high-intensity electric field application will cause arrhythmogenic responses through a transient rupture of sarcolemma. with different subcellular events in ventricular cells under normal and pathological conditions.