EFFECT OF CAMP-DEPENDENT PROTEIN-KINASE ON CATECHOLAMINE SECRETION FROM BOVINE ADRENAL CHROMAFFIN CELLS

We examined the role of cAMP-dependent protein kinase in Ca2+-elicited catecholamine secretion from bovine adrenal chromaffin cells. When th e digitonin-treated cells were incubated with the catalytic subunit of cAMP-dependent protein kinase, the secretion of catecholamines from t he cells occurred in the absence of Ca2+. The effect of the catalytic subunit was dependent on its activity (50-100 units/ml) and the presen ce of ATP-Mg2+ in the incubation medium. However, incubation of the ce lls with the regulatory subunit of cAMP-dependent protein kinase did n ot affect the secretion, Ca2+ (43 nM-10 mu M) also increased the secre tion, which was ATP-Mg2+-dependent. The catalytic subunit (25-200 unit s/ml) enhanced the Ca2+-evoked secretion at the suboptimal but not opt imal Ca2+ concentration, which induced maximal secretion. A potent syn thetic peptide inhibitor of cAMP-dependent protein kinase abolished th e catalytic subunit-induced secretion, but not the Ca2+-evoked secreti on. On the other hand, K-252a, a potent inhibitor of protein kinases, inhibited both the catalytic subunit-induced and the Ca2+-evoked secre tion, but not KT5823, a much less potent inhibitor of protein kinases. These results strongly suggest that the catalytic subunit of cAMP-dep endent protein kinase produces the secretion of catecholamines via pro tein phosphorylation. The results further suggest that the cAMP-depend ent protein kinase does not participate in an intrinsic process of Ca2 +-elicited secretion but it may act as a modulator.