Up-regulation of functional voltage-dependent sodium channels by cyclic AMP-dependent protein kinase in adrenal medulla

Treatment of cultured bovine adrenal chromaffin cells with dbcAMP increased [H-3]STX binding with an EC(50) of 126 mu M and a half-effective time of 12 h; dbcAMP (1 mM x 18 h) raised the B-max approximately 1.5-fold without altering the K-d value. Forskolin (0.1 mM) or IBMX (0.3 mM) also increased [H-3]STX binding, while dbcCMP had no effect. Effects of dbcAMP and forskolin were abolished by H-89, an inhibitor of cAMP-dependent protein kinase. Cycloheximide (10 mu g/ml) and actinomycin D (10 mu g/ml), inhibitors of protein synthesis, nullified the stimulatory effect of dbcAMP, whereas tunicamycin, an inhibitor of protein glycosylation, had no effect. Treatment with dbcAMP augmented veratridine-induced Na-22 influx, Ca-45 influx via voltage-dependent Ca channels and catecholamine secretion, while the same treatment did not alter Ca-45 influx and catecholamine secretion caused by high K (a direct activation of voltage-dependent Ca channels) [25]. Na influx via single Na channel calculated from Na-22 influx and [H-3]STX binding was quantitatively similar between non-treated and dbcAMP-treated cells. Brevetoxin allosterically enhanced veratridine-induced Na influx approximately 3-fold in dbcAMP-treated cells as in non-treated cells. These results suggest that cAMP-dependent protein kinase is involved in the modulation of Na channel expression in adrenal medulla.