Effects of cytosolic ATP and other nucleotides on Ca2+-activated K+ channels in cultured bovine adrenal chromaffin cells

The effects of cytosolic ATP on Ca2+-dependent K+ (K-Ca) channel activation in cultured bovine adrenal chromaffin cells were investigated by using single-channel recording patch-clamp techniques. Application of ATP to the intracellular surface of excised inside-out patches activated K-Ca channels in a dose-dependent manner at 30 mu M to 10 mM. The K-Ca channels also were activated by 3 mM of adenosine 5'-O-(3'-thiotriphosphate) (ATP gamma S), a non-hydrolyzable analogue of ATP, but not by 5'-adenylylimidodiphosphate (AMP-PNP) (from 300 mu M to 3 mM). Furthermore, other nucleotides also activated K-Ca channels in inside-out patches. This modulation took place without addition of exogenous protein kinase and was dependent on the presence of Mg2+ in the bathing solution. Staurosporine, a non-specific kinase inhibitor, or H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide), a cAMP-dependent protein kinase inhibitor, was unable to alter ATP-mediated K-Ca channel activation. Following complete removal of Mg2+, a higher concentration of ATP (10 mM) and other nucleotides was required to activate K-Ca channels; however, Mg2+ was ineffective in altering the activation of K-Ca channels by itself. It is concluded that intracellular ATP and other nucleotides activate K-Ca channels directly. These nucleotides may regulate catecholamine release by changing the cell membrane potential in adrenal chromaffin cells. (C) 1998 Elsevier Science B.V. All rights reserved.