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 activ ation 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 activa ted 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'-thiotr iphosphate) (ATP gamma S), a non-hydrolyzable analogue of ATP, but not by 5'-adenylylimidodiphosphate (AMP-PNP) (from 300 mu M to 3 mM). Fur thermore, other nucleotides also activated K-Ca channels in inside-out patches. This modulation took place without addition of exogenous pro tein kinase and was dependent on the presence of Mg2+ in the bathing s olution. Staurosporine, a non-specific kinase inhibitor, or H-89 ocinn amylamino)ethyl]-5-isoquinoline-sulfonamide), a cAMP-dependent protein kinase inhibitor, was unable to alter ATP-mediated K-Ca channel activ ation. Following complete removal of Mg2+, a higher concentration of A TP (10 mM) and other nucleotides was required to activate K-Ca channel s; however, Mg2+ was ineffective in altering the activation of K-Ca ch annels by itself. It is concluded that intracellular ATP and other nuc leotides activate K-Ca channels directly. These nucleotides may regula te catecholamine release by changing the cell membrane potential in ad renal chromaffin cells. (C) 1998 Elsevier Science B.V. All rights rese rved.