MODULATION OF CA2+ ACTIVATED K+ CHANNELS BY MG2+ AND ATP IN FROG OXYNTIC CELLS

Ca2+-activated K+ channels in the basolateral plasma membrane of bullf rog oxynticopeptic cells are intimately involved in the regulation of acid secretion. Patch-clamp techniques were applied to study the regul ating mechanism of these channels. In the excised inside-out configura tion, intracellular Mg2+ decreased channel activity in a dose-dependen t manner. In the absence of Mg2+, administration of adenosine 5'-triph osphate (ATP) to the cytoplasmic side also inhibited channel activity. On the other hand, in the presence of Mg2+, addition of ATP markedly increased channel activity. At a fixed concentration of free Mg2+, the Mg-ATP complex caused channel activation and shifted the dose respons e relationship between channel activity and the intracellular Ca2+ con centration to the left. A nonhydrolysable ATP analogue, adenosine 5'-[ beta,gamma-imido]triphosphate (AMP-PNP) adenylyl [beta,gamma-methylene ]diphosphate (AMP-PCP), could not substitute for ATP in channel activa tion, but a hydrolysable ATP analogue, adenosine 5'-O-(3-thiotriphosph ate) (ATP[gamma S]) could do so. Furthermore, application of alkaline phosphatase to the cytoplasmic side inhibited channel activity. These results demonstrate that Ca2+-activated K+ channels are regulated by M g2+ and ATP, and suggest that a phosphorylation reaction may be involv ed in the regulation mechanism of these channels.