Intracellular ADP activates K+ channels that are inhibited by ATP in an insulin‐secreting cell line

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Abstract
The effect of ADP on ATP‐sensitive K+ channels in the insulin‐secreting RINm5F cell line has been investigated with the help of single‐channel current recording from saponin‐permeabilized cells. ADP (100–500 μM) markedly activates K+ channels when added to the bath solution in contact with the membrane inside. ADP‐β‐S cannot mimick this effect. During sustained ATP (500 μM)‐evoked inhibition of K+ channel opening, 500 μM ADP markedly and reversibly activates the channels. Conversely ATP markedly reduces the opening probability of ADP‐activated channels. It is suggested that the physiological control of K+ channel opening in the insulin‐secreting cells is mediated by changes in ATP/ADP ratio rather than being solely determined by the ATP concentration.