2, 5-di(tert-butyl)-1, 4-benzohydroquinone -a novel mobilizer of the inositol 1,4,5-trisphosphate-sensitive ca2+ pool

Abstract

Isolated hepatocytes and the isolated perfused rat liver have been used to study the alterations of cytosolic free Ca2+ concentration ([Ca2+]i) produced by 2,5-di(tert-butyl)-l.4-benzohydroquinone (tBuBHQ), a potent inhibitor of hepatic microsomal Ca2+ sequestration (Moore. G.A., McConkey. D.J., Kass, G.E.N., OBrien, P.J. and Orrenius, S. FEBS Lett.,224, 331-336). (1987). Addition of tBuBHQ to isolated hepatocytes caused a rapid increase in [Ca2+]i which was similar in magnitude to the [Ca2+]i elevation induced by the Ca2+ mobilizing hormone, vasopressin. In contrast with vasopressin which caused a Ca2+ transient, tBuBHQ elevated [Ca2+]i to a new steady state that was maintained for up to 15-20min. When vasopressin was administered during the tBuBHQ-induced period of elevated [Ca2+]i. [Ca2+]i, rapidly returned to basal levels. Similarly, if vasopressin was administered just prior to tBuBHQ, the resultant tBuBHQ-dependent change in [Ca2+]i was transient. and not sustained. The hydroquinone mobilized the same intracellular Ca2+ pool as inositol 1,4,5-trisphosphate. but tBuBHQ did not produce any detectable inositol polyphosphate accumulation. IBuBHQ stimulated glucose release from perifused hepatocytes. mimicking the effect of vasopressin. In the perfused liver, tBuBHQ infusion produced a single, slow and prolonged release of Ca2+ into the perfusate and inhibition of subsequent vasopressin-induced Ca2+ effluxes. Inhibition of the response to vasopressin was reversed over time, and closely correlated with the extent of inhibition of both Ca2+ sequestration and (Ca2+-Mg2+)-ATPase activity in microsomes isolated from the isolated perfused liver. The present results are consistent with tBuBHQ inhibiting ATP-dependent Ca2+ sequestration by a direct effect on the endoplasmic reticular Ca2+ pump, which results in net Ca2+ release and elevation of [Ca2+]i. Furthermore. vasopressin appears to stimulate active removal of increased [Ca2+] from the hepatocyte cytosol by a mechanism which does not depend on reuptake of Ca2+ into the endoplasmic reticulum 2,5-Di(tert-butyl) -l,4-benmhydroquinone. calcium. hepatocytes. perfused liver, endoplasmic reticulum Show more