Effects of some sterically hindered phenols on whole-cell Ca2+ current of guinea-pig gastric fundus smooth muscle cells

Abstract

1. The aim of the present study was to investigate the effects of extracellular application of some sterically-hindered phenols, namely 3-t-butyl-4-hydroxyanisole (BHA), 3,5-di-t-butyl-4-hydroxyanisole (DTBHA) and the dimer of BHA, 2,2′-dihydroxy-3,3′-di-t-butyl-5,5′-dimethoxydiphenyl (DIBHA), on the whole-cell Ca2+ current (ICa) of freshly isolated smooth muscle cells from the guinea-pig gastric fundus, in the presence of a range of Ca2+ concentrations (1 -5 mM) using the patch-clamp technique. The influx of Ca2+ had characteristics of L-type ICa (ICa(L)). 2. BHA as well as DTBHA inhibited ICa(L) in a concentration-dependent manner, during depolarization to 10 mV from a holding potential of -50 mV. Bath application of BHA (50 μM) and DTBHA (30 μM) decreased ICa(L) by 48.9% and 45.2%, respectively. This inhibition was only partially reversible. In contrast, DIBHA (up to 50 μM) was devoided of effects on ICa(L). 3. BHA inhibition of ICa(L) was voltage-dependent and inversely related to the external concentration of Ca2+. On the other hand, DTBHA inhibition was only voltage-dependent. 4. BHA and DTBHA shifted the voltage range of the steady-state inactivation curve to more negative potentials by 8 mV at the mid-potential of the curve, without affecting the activation curve. Furthermore, BHA and DTBHA did not modify the time-course of the current decay. 5. We conclude that the inhibition of ICa(L) by BHA and DTBHA is qualitatively similar to that of a Ca2+ channel blocker and is characterized by the stabilizing effect of the inactivated state of the channel.