Protein Kinase C Activates ATP-Sensitive K + Current in Human and Rabbit Ventricular Myocytes

Abstract

Abstract Mediators involved in ischemic preconditioning, such as adenosine and norepinephrine, can activate protein kinase C (PKC), and a variety of observations suggest that both PKC and ATP-sensitive K + current (I KATP ) play essential roles in ischemic preconditioning. PKC is therefore a candidate to link receptor binding to I KATP activation, but it has not been shown whether and how PKC can activate I KATP in the heart. The present study was designed to determine whether PKC can activate I KATP in rabbit and human ventricular myocytes. Under conditions designed to minimize Na + and Ca 2+ currents, dialysis of rabbit ventricular myocytes with pipette solutions containing reduced [ATP] elicited I KATP , with a 50% effective concentration (EC 50 ) of 260 μmol/L. In cells that failed to show I KATP under control conditions, superfusion with 1 μmol/L phorbol 12,13-didecanoate (PDD) elicited I KATP in a fashion that depended on pipette [ATP], with an [ATP] EC 50 of 601 μmol/L. PDD-induced I KATP activation was concentration dependent, with an EC 50 of 7.1 nmol/L. The highly selective PKC inhibitor bisindolylmaleimide totally prevented I KATP activation by PDD, and in blinded experiments, 1 μmol/L PDD elicited I KATP in eight of nine cells, whereas its non–PKC-stimulating analogue 4α-PDD failed to elicit I KATP in any of the five cells tested ( P =.003). Similar experiments were conducted in human ventricular myocytes and showed that 0.1 μmol/L PDD elicited I KATP at pipette [ATP] of 100 and 400 μmol/L (five of five cells at each concentration) but not at 1 mmol/L [ATP] (none of five cells). We conclude that PKC activates I KATP in rabbit and human ventricular myocytes by reducing channel sensitivity to intracellular ATP. This finding has potentially important implications for understanding the mechanisms of ischemic preconditioning.