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

1 The aim of the present study was to investigate the effects of 2,5-di-t-b utyl-1,4-benzohydroquinone (BHQ), an inhibitor of the sarco-endoplasmic ret iculum Ca2+-ATPase (SERCA), on the whole-cell voltage-dependent L-type Ca2 current of freshly isolated smooth muscle cells from the rat tail artery u sing the patch-clamp technique. 2 BHQ, added to the perfusion solution, reduced I-Cat(L) in a concentration - (IC50 = 66.7 muM) and voltage-dependent manner. This inhibition was only partially reversible. 3 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, wit hout affecting the activation curve as well as the time course of I-Ca(L) i nactivation. 4 Preincubation of the cells either with 10 mum cyclopiazonic acid, a SERCA inhibitor, or with 3 mm diethyldithiocarbamate, an inhibitor of intracellu lar superoxide dismutase (SOD), did not modify BHQ inhibition of I-Ca(L). O n the contrary, this effect was no longer evident when SOD (250 u ml(-1)) w as added to the perfusion medium. 5 Either in the presence or in the absence of cells, BHQ gave rise to super oxide anion formation, which was markedly inhibited by the addition of SOD. 6 These results indicate that, at micromolar concentrations, BHQ inhibits v ascular by giving rise to the formation of superoxide anion which in turn i mpairs the channel function.