Effect of the intracellular calcium concentration chelator BAPTA acetoxy-methylester on action potential duration in canine ventricular myocytes

Journal of Physiology and Pharmacology : an Official Journal of the Polish Physiological Society
Balázs HorváthPéter P Nánási

Abstract

Intracellular calcium concentration ([Ca2+]i) is often buffered by using the cell-permeant acetoxy-methylester form of the Ca2+ chelator BAPTA (BAPTA-AM) under experimental conditions. This study was designed to investigate the time-dependent actions of extracellularly applied BAPTA-AM on action potential duration (APD) in cardiac cells. Action potentials were recorded from enzymatically isolated canine ventricular myocytes with conventional sharp microelectrodes. The effect of BAPTA-AM on the rapid delayed rectifier K+ current (IKr) was studied using conventional voltage clamp and action potential voltage clamp techniques. APD was lengthened by 5 μM BAPTA-AM - but not by BAPTA - and shortened by the Ca2+ ionophore A23187 in a time-dependent manner. The APD-lengthening effect of BAPTA-AM was strongly suppressed in the presence of nisoldipine, and enhanced in the presence of BAY K8644, suggesting that a shift in the [Ca2+]i-dependent inactivation of L-type Ca2+ current may be an important underlying mechanism. However, in the presence of the IKr-blocker dofetilide or E-4031 APD was shortened rather than lengthened by BAPTA-AM. Similarly, the APD-lengthening effect of 100 nM dofetilide was halved by the pretreatment with BAPTA-AM...Continue Reading

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