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

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)).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).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.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.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.