PROTECTIVE EFFECTS OF CALCIUM-CHANNEL BLOCKERS ON ACUTE BROMOBENZENE TOXICITY TO ISOLATED RAT HEPATOCYTES - INHIBITION OF PHENYLEPHRINE-INDUCED CALCIUM OSCILLATIONS

Background and Methods: Protective effects of verapamil, nifedipine, d iltiazem, and ethylene glycol tetraacetic acid (EGTA) on acute bromobe nzene (BB) toxicity to rat hepatocytes were evaluated, and cytosolic [ Ca2+](i) was monitored in single BB-exposed rat hepatocytes. Additiona lly, the effect of nifedipine on phenylephrine-stimulated calcium osci llations was investigated. Results: BE at 0.8-2.4 mM increased the lac tate dehydrogenase (LDH) leakage rate dose-dependently. Pretreatment w ith verapamil (25-35 mu M), nifedipine (35-45 mu M), diltiazem (25 mu M), or EGTA (1.5-5 mM) markedly attenuated the BE-induced (1.6 mM) LDH leakage rate during 2 h of incubations. BB did not cause any detectab le acute change in [Ca-2+](i). BB interfered with phenylephrine-stimul ated calcium oscillations, by blocking the oscillations in 58% of the cells and reducing the oscillation frequency in the rest. Nifedipine ( 100 and 200 mu M) blocked the phenylephrine-induced calcium oscillatio ns completely in 55% and 88% of the cells, respectively. Conclusions: The findings demonstrate that verapamil, nifedipine, diltiazem, and EG TA significantly protect rat hepatocytes against BB toxicity. BB inter feres with phenylephrine-stimulated calcium oscillations. Nifedipine i nhibits the oscillations at doses higher than those exerting a protect ive effect.