ISCHEMIC CARDIOPROTECTION BY ATP-SENSITIVE K+ CHANNELS INVOLVES HIGH-ENERGY PHOSPHATE PRESERVATION

We previously demonstrated that ATP-sensitive K+ channels (K(ATP)) protect the guinea pig myocardium against ischemia-reperfusion injury (Cole et al., Circ. Res. 69: 571-581, 1991), but the cellular alterations leading to ischemic injury affected by K(ATP) remain to be defined. This study investigates the relationship between activation of K(ATP) and preservation of high-energy phosphates during global no-flow ischemia in arterially perfused guinea pig right ventricular walls. Electrical and mechanical activity were recorded via intracellular microelectrodes and a force transducer. Glibenclamide (10 and 50 muM) and pinacidil (10 muM) were used to modulate K(ATP). ATP and creatine phosphate (CP) levels were determined at the end of no-flow ischemia by enzymatic analysis. Preparations were subjected to 1) 20 min no-flow +/- glibenclamide (10 or 50 muM), 2) 30 min no-flow +/- pinacidil (10 muM) or pinacidil (10 muM) and glibenclamide (50 muM), or 3) 40 or 50 min of control perfusion before rapid freezing in liquid nitrogen. Pinacidil (10 muM) enhanced ischemic shortening of action potential duration (APD) and early contractile failure, prevented ischemic contracture, and inhibited high-energy phosphate depletion during ischemia. Glibenclamide (50 muM) inhibited the effects of pinacidil (10 muM) on electromechanical function and preservation of ATP and CP. Glibenclamide (10 muM) alone inhibited the early decline in APD and produced earlier ischemic contracture but did not enhance ATP or CP depletion compared with untreated tissues during 20 min of no-flow. Glibenclamide (50 muM) produced a greater inhibition of APD shortening in early ischemia, further decreased the latency to ischemic contracture, and caused enhanced ischemic depletion of ATP. The data indicate the changes in electrical activity induced by K(ATP) indirectly preserve high-energy phosphates and reduce injury associated with ischemia. However, the data also suggest the possible presence of additional mechanisms for cardioprotection by K(ATP).