Adenosine-induced activation of ATP-sensitive K+ channels in excised membrane patches is mediated by PKC

Both protein kinase C (PKC) and adenosine receptor activation have been shown to enhance ATP-sensitive K+ (K-ATP) channels. The present studies were designed to determine whether PKC mediates adenosine effects on the K-ATP channel. The dependence of K-ATP channel activity (nP(o)) on intracellular ATP concentration ([ATP](i)) was determined in excised rabbit ventricular membrane patches. External adenosine (100 mu M in the pipette solution) significantly increased K-ATP nP(o) at all [ATP](i) between 5 and 50 mu M by decreasing channel sensitivity to [ATP](i) (dissociation constant increased from 7.4 +/- 0.8 to 22.2 +/- 3.1 mu M, P < 0.001), an effect blocked by the adenosine receptor antagonist 8-phenyltheophylline (10 mu M). When the highly selective PKC blocker bisindolylmaleimide (BIM) was included in the internal (bath) solution, the K-ATP-stimulating action of adenosine was prevented. The addition of BIM to the superfusate rapidly inhibited K-ATP channels activated by adenosine. Endogenous PKC activation by phorbol 12,13-didecanoate (PDD), but not administration of the inactive congener 4 alpha-PDD, enhanced K-ATP activity. Internal guanosine 5'-O-(2-thiodiphosphate) prevented K-ATP activation by adenosine, an effect, which could be overridden by exposure to PDD. We conclude that PKC mediates adenosine activation of K-ATP channels in excised membrane patches in a membrane-delimited fashion.