1,1-Dichloroethylene inhibition of liver microsomal calcium pump in vitro

Abstract

Rat liver microsomes were preincubated with 1,1-dichloroethylene (1,1-DCE) and a NADPH-generating system for 20 min, then ER calcium pump activity determined. Calcium pump activity was inhibited as a function of 1,1-DCE concentration. 1,1-DCE did not inhibit in the absence of a NADPH-generating system. Calcium pump activity was inhibited to a significantly greater extent by 1,1-DCE in microsomes isolated from phenobarbital-pretreated rats than in microsomes from control rats. These studies suggest that the mixed function oxidase system generates a metabolite that attacks the endoplasmic reticulum (ER) calcium pump. The time course of pump inhibition by 1,1-DCE and CCl 4 were compared in vitro. 1,1-DCE produced inhibition of the calcium pump at a substantially slower rate. CCl 4 at 1 μliter/ml inhibited calcium pump activity within l min. 1,1-DCE did not produce significant inhibition within 1 min, but produced 58 ± 5% inhibition by 20 min. CCl 4 but not 1,1-DCE, produced lipid peroxidation as judged by malonic dialdehyde production. It is possible that lipid peroxidation contributes to the rapid course of inhibition produced by CCl 4. These studies suggest that metabolic activation, but not lipid peroxidation, is a prerequisite for inhibition of the liver ER calcium pump by chlorinated hydrocarbon hepatotoxins in vitro.