Effect of tetraethylammonium chloride on action potential in cardiac Purkinje fibers

Abstract

Intracellular loading with 20 mM tetraethylammonium chloride (TEA) diffusing through the cut end of the preparations prolonged action potential duration (APD) in dog Purkinje fibers without changing maximum diastolic potential, overshoot and dV/dtmax [maximum change in volume over time]. The APD was was prolonged at all rates of stimulation, but, contrary to the normal rules, APD increased more after longer than after shorter interstimulus intervals. TEA increased the number of beats required to achieve the new steady-state APD after an abrupt change in the rate of stimulation. The effect of varying extracellular K concentration on maximal diastolic potential suggested that intracellular loading with TEA had no effect on the time-independent background outward current (IKl). If the TEA effects result from the reduction of time-dependent slow outward current (IXl), a hypothesis concerning the role of IXl in the regulation of APD at slow heart rates can be proposed.