Verapamil and diltiazem inhibit receptor-operated calcium channels and intracellular calcium oscillations in rat hepatocytes.

Fura-2 loaded rat hepatocytes were used to determine whether the L-type channel blockers, verapamil and diltiazem, affect receptor-operated calcium channels (ROCCs). The flux through ROCCs was followed by quenching of fura-2 fluorescence due to the influx of extracellular Mn2+ induced by vasopressin. Verapamil as well as diltiazem inhibited vasopressin-stimulated Mn2+ influx in a dose-dependent manner up to 60% at concentrations of 200-400 microM. Furthermore, both inhibitors decreased significantly the frequency of phenylephrine-induced oscillation of [Ca2+]i. The experimental findings indicate that L-type channel blockers inhibit ROCCs in rat hepatocytes.