Effects of cytosolic ATP and other nucleotides on Ca 2+-activated K + channels in cultured bovine adrenal chromaffin cells

Abstract

The effects of cytosolic ATP on Ca 2+-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 μM to 10 mM. The K Ca channels also were activated by 3 mM of adenosine 5′- O-(3′-thiotriphosphate) (ATP γS), a non-hydrolyzable analogue of ATP, but not by 5′-adenylylimidodiphosphate (AMP-PNP) (from 300 μM 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 Mg 2+ 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 Mg 2+, a higher concentration of ATP (10 mM) and other nucleotides was required to activate K Ca channels; however, Mg 2+ 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.