2,5-Di-t-butyl-1,4-benzohydroquinone (BHQ) inhibits vascular L-type Ca2+ channel via superoxide anion generation

The aim of the present study was to investigate the effects of 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), an inhibitor of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), on the whole-cell voltage-dependent L-type Ca(2+) current (I(Ca(L))) of freshly isolated smooth muscle cells from the rat tail artery using the patch-clamp technique. BHQ, added to the perfusion solution, reduced I(Ca(L)) in a concentration- (IC(50)=66.7 microM) and voltage-dependent manner. This inhibition was only partially reversible. BHQ shifted the voltage dependence of the steady-state inactivation curve to more negative potentials by 7 mV in the mid-potential of the curve, without affecting the activation curve as well as the time course of I(Ca(L)) inactivation. Preincubation of the cells either with 10 microM cyclopiazonic acid, a SERCA inhibitor, or with 3 mM diethyldithiocarbamate, an inhibitor of intracellular superoxide dismutase (SOD), did not modify BHQ inhibition of I(Ca(L)). On the contrary, this effect was no longer evident when SOD (250 u ml(-1)) was added to the perfusion medium. Either in the presence or in the absence of cells, BHQ gave rise to superoxide anion formation, which was markedly inhibited by the addition of SOD. These results indicate that, at micromolar concentrations, BHQ inhibits vascular I(Ca(L)) by giving rise to the formation of superoxide anion which in turn impairs the channel function.