Protein kinase C activates ATP-sensitive K+ current in human and rabbit ventricular myocytes

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 Ca2+ currents, dialysis of rabbit ventricular myocytes with pipette solutions containing reduced [ATP] elicited I-KATP, with a 50% effective concentration (EC(50)) of 260 mu mol/L. In cells that failed to show I-KATP under control conditions, superfusion with 1 mu mol/L phorbol 12,13-didecanoate (PDD) elicited I-KATP in a fashion that depended on pipette [ATP], with an [ATP] EC(50) of 601 mu mol/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 mu mol/L PDD elicited I-KATP in eight of nine cells, whereas its non-PKC-stimulating analogue 4 alpha-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 mu mol/L PDD elicited I-KATP at pipette [ATP] of 100 and 400 mu mol/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.