MECHANISM OF CYCLIC-AMP FACILITATION OF STIMULATION-EVOKED CATECHOLAMINE RELEASE IN ADRENAL CHROMAFFIN CELLS .2. INHIBITION OF NA+,K+-ATPASE BY CYCLIC-AMP

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 [gamma-P-32]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 [gamma-P-32]ATP hydrolysis and the inhibitor of the protein kinase blocked the catalytic subunit-induced reduction of ATP hydrolysis. 8-Br cyclic AMP and forskolin inhibited Rb-86 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.