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

Abstract

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 μM in the pipette solution) significantly increased K(ATP) nP(o) at all [ATP](i) between 5 and 50 μM by decreasing channel sensitivity to [ATP](i) (dissociation constant increased from 7.4 ± 0.8 to 22.2 ± 3.1 μM, P < 0.001), an effect blocked by the adenosine receptor antagonist 8-phenyltheophylline (10 μM). 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 4α-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.