Dual control by ATP and acetylcholine of inwardly rectifying K+ channels in bovine atrial cells

Whole-cell and single-channel recordings were used to study an ionic current activated by extracellular adenosine 5′-triphosphate (ATP) applied to calf atrial cells. ATP (K _d ≈ 10μM) elicited an inwardly rectifying current that reversed nearE _K and was blocked by external Cs⁺ (10 mM). Under identical conditions, adenosine had no effect. Cell-attached patch recordings revealed an ATP-activated channel with a slope conductance of about 30 pS. At both the whole-cell and single-channel levels, the channels activated by ATP seemed nearly identical to the potassium channels activated by acetylcholine (ACh) in the same cells. However, the effects of ATP were not affected by atropine, suggesting that ATP does not interact with the same receptors as ACh. In some cells, whole-cell currents of similar magnitude were activated by ACh alone, ATP alone, or ACh and ATP applied together. These results suggest that calf atrial cells possess a population of inwardly rectifying potassium channels that are controlled jointly by two populations of receptors selective for ACh and ATP.