Veratridine causes the Ca²⁺-dependent increase in diacylglycerol formation and translocation of protein kinase C to membranes in cultured bovine adrenal medullary cells

Summary

Our previous studies suggested that protein kinase C is involved in the veratridine (an activator of voltage-dependent Na⁺ channels)-induced phosphorylation and activation of tyrosine hydroxylase as well as the synthesis of catecholamines in adrenal medulla (Uezono et al. 1989). In the present study, we investigated whether treatment of cultured bovine adrenal medullary cells with veratridine causes the accumulation of diacylglycerol, a physiological activator of protein kinase C and the translocation of protein kinase C from cytosol to membrane, a process required for protein kinase C activation. Veratridine (100 μmol/l) increased diacylglycerol level about 2.2 fold in a monophasic manner, with peaking at 5 min and declining toward the basal level within 20 min. Veratridine also increased membrane protein kinase C from 15.6% to 26.9% of total protein kinase C in a timecourse similar to that of diacylglycerol accumulation. Both stimulatory effects of veratridine were inhibited by tetrodotoxin and not observed in Ca²⁺-free, EGTA-containing medium. Amiloride, an inhibitor of Na⁺/Ca²⁺ and Na⁺/H⁺ exchange, did not alter veratridine-induced events. These results suggest that veratridine-induced Ca²⁺ influx contributes to the accumulation of diacylglycerol and the activation of protein kinase C in adrenal medullary cells.