Anion channels influence ECC by modulating L-type Ca2+ channel in ventricular myocytes

Abstract

Anion channels are extensively expressed in the heart, but their roles in cardiac excitation-contraction coupling (ECC) are poorly understood. We, therefore, investigated the effects of anion channels on cardiac ventricular ECC. Edge detection, fura 2 fluorescence measurements, and whole cell patch-clamp techniques were used to measure cell shortening, the intracellular Ca2+ transient, and the L-type Ca2+ current ( I Ca,L) in single rat ventricular myocytes. The anion channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and niflumic acid reversibly inhibited the Ca2+ transients and cell shortening in a dose-dependent manner. Comparable results were observed when the majority of the extracellular Cl− was replaced with the relatively impermeant anions glutamate (Glt−) and aspartate (Asp−). NPPB and niflumic acid or the Cl− substitutes did not affect the resting intracellular Ca2+ concentration but significantly inhibited I Ca,L. In contrast, replacement of extracellular Cl− with the permeant anions NO[Formula: see text], SCN−, and Br− supported the ECC and I Ca,L, which were still sensitive to blockade by NPPB. Exposure of cardiac ventricular myocytes to a hypotonic bath solution enhanced the amplitude of cell shortening and supported I Ca,L, whereas hypertonic stress depressed the contraction and I Ca,L. Moreover, cardiac contraction was completely abolished by NPPB (50 μM) under hypotonic conditions. It is concluded that a swelling-activated anion channel may be involved in the regulation of cardiac ECC through modulating L-type Ca2+ channel activity.