2,5‐Di(tert‐butyl)‐1,4‐benzohydroquinone — a novel inhibitor of liver microsomal Ca2+ sequestration

Treatment of rat liver microsomes with 2,5‐di(tert‐butyl)‐1,4‐benzohydroquinone caused a dose‐related inhibition (K i⋍1 μM) of ATP‐dependent Ca2+ sequestration. This was paralleled by a similar impairment of the microsomal Ca2+ ‐stimulated ATPase activity. In contrast, the hydroquinone failed to induce Ca2+ release from Ca2+ ‐loaded liver mitochondria (supplied with ATP), and inhibited neither the mitochondrial F1F0‐ATPase nor the Ca2+ ‐stimulated ATPase activity of the hepatic plasma membrane fraction. The inhibition of microsomal Ca2+ sequestration was not associated with any apparent alteration of membrane permeability or loss of other microsomal enzyme activities or modification of microsomal protein thiols. These findings suggest that 2,5‐di(tert‐butyl)‐1,4‐benzohydroquinone is a potent and selective inhibitor of liver microsomal Ca2+ sequestration which may be a useful tool in studies of Ca2+ fluxes in intact cells and tissues.