Mechanism of cyclic AMP facilitation of stimulation-evoked catecholamine release in adrenal chromaffin cells—II. Inhibition of Na+,K+-ATPase by cyclic AMP

Abstract

The ability of cyclic AMP to inhibit Na + ,K + -ATPase activity in adrenal medulla was examined to elucidate mechanisms of cyclic AMP stimulatory modulations in catecholamine (CA) secretion from adrenal gland. Cyclic AMP, 10 −7 –10 −4 M, was demonstrated to inhibit Na + ,K + -ATPase activity of microsomes from bovine adrenal medulla. 8-Br cyclic AMP and forskolin reduced [γ- 32 P]ATP hydrolysis by digitonin-permeabilized chromaffin cells and this reduction of ATP hydrolysis was due to an inhibition of Na + ,K + -ATPase. Catalytic subunit of cyclic AMP-dependent protein kinase also reduced [γ- 32 P]ATP hydrolysis and the inhibitor of the protein kinase blocked the catalytic subunit-inducted reduction of ATP hydrolysis. 8-Br cyclic AMP and forskolin inhibited 86 Rb uptake into cultured chromaffin cells. From these results, the ability of cyclic AMP to inhibit adrenomedullary Na + ,K + -ATPase was shown in crude membrane fraction, in leaky cell preparation and also in intact cells.