ATP-dependent calcium uptake by rat liver plasma membrane vesicles. Effect of alkylating hepatotoxins in vivo.

Lethal cell injury from hepatotoxic drugs has been postulated to result from an alteration in cell Ca2+ homeostasis. ATP-dependent Ca2+ uptake by the plasma membrane has a sulfhydryl-dependent functional moiety and, therefore, could be vulnerable to chemically reactive drug intermediates. Thus, alkylating hepatotoxins given in vivo were examined for their ability to inhibit Ca2+ accumulation by plasma membrane vesicles isolated from livers of adult male rats. ATP-dependent Ca2+ accumulation was decreased 62% by bromobenzene, 76% by acetaminophen, and 92% by CCl4. Mitochondrial Ca2+ uptake was minimally affected by the toxins, and only CCl4 affected Ca2+ accumulation by liver microsomes. The effect of acetaminophen on plasma membrane Ca2+ uptake was apparent as early as 45 min postdose. Depletion of protective intracellular GSH by diethyl maleate treatment (400 mg/kg) alone minimally decreased control plasma membrane uptake activity, although the GSH depletion markedly potentiated the effect of acetaminophen on the plasma membrane and on necrosis. Alkylation of sites on the plasma membrane may be a key chemical-macromolecule interaction in drug-induced liver necrosis, and inhibition of plasma membrane Ca2+ regulation may provide a connecting link between the alkylation hypothesis and the perturbed Ca2+ homeostasis hypothesis of lethal cell injury.