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, diltiazem, and ethylene glycol tetraacetic acid (EGTA) on acute bromobenzene (BB) toxicity to rat hepatocytes were evaluated, and cytosolic [Ca²⁺]_i was monitored in single BB-exposed rat hepatocytes. Additionally, the effect of nifedipine on phenylephrine-stimulated calcium oscillations was investigated. Results: BB at 0.8-2.4 mM increased the lactate dehydrogenase (LDH) leakage rate dose-dependently. Pretreatment with verapamil (25-35 u.M), nifedipine (35-45 μM), diltiazem (25 μM), or EGTA (1.5-5 μM) markedly attenuated the BB-induced (1.6 mM) LDH leakage rate during 2 h of incubations. BB did not cause any detectable acute change in [Ca²⁺]_i. BB interfered with phenylephrine-stimulated calcium oscillations, by blocking the oscillations in 58% of the cells and reducing the oscillation frequency in the rest. Nifedipine (100 and 200 μM) blocked the phenylephrineinduced calcium oscillations completely in 55% and 88% of the cells, respectively. Conclusions: The findings demonstrate that verapamil, nifedipine, diltiazem, and EGTA significantly protect rat hepatocytes against BB toxicity. BB interferes with phenylephrine-stimulated calcium oscillations. Nifedipine inhibits the oscillations at doses higher than those exerting a protective effect.