IS POTASSIUM CHANNEL OPENING AN EFFECTIVE FORM OF PRECONDITIONING BEFORE CARDIOPLEGIA

Background. Opening of adenosine triphosphate-sensitive potassium chan nnels might be one of the mechanisms by which preconditioning preserve s the myocardium against ischemic damage. They present study was there fore designed to compare th e protective efficacy of ischemic precondi tioning with that of pharmacologic preconditioning involving the use o f a potassium channel opener in a surgically relevant model of cold ca rdioplegic arrest. Methods. Thirty isolated isovolumic rat hearts were subjected to 2 hours of potassium arrest at an average myocardial tem perature of 23 degrees C, followed by 1 hour of of reperfusion. Three groups (n = 10 per group) were studied: (1) control (no prearrest inte rvention); (2) ischemic preconditioning, achieved with 5 minutes of no -flow ischemia followed by 5 minutes of reperfusion before arrest; and (3) pharmacologic preconditioning, achieved with a 5-minute infusion of the potassium channel opener nicorandil (10 mu mol/L) followed by 5 minutes of drug-free perfusion before arrest. Standard functional ind ices were measured at multiple times during reperfusion, at the end of which pressure-volume curves were constructed and compared With those obtained at baseline. Results. Both ischemically and pharmacologicall y preconditioned hearts recovered systolic and diastolic function to a significantly greater extent than the controls. There was no differen ce in the recovery patterns between the forms of preconditioning. Howe ver, analysis of the postischemic pressure-volume curves demonstrated that nicorandil-preconditioned hearts incurred the smallest losses of compliance throughout the ischemia-reperfusion sequence. Conclusions. The protective effects of a standard ischemic preconditioning challeng e on functional recovery after an episode of moderately hypothermic ca rdioplegic arrest can be duplicated by pharmacologic opening of adenos ine triphosphate-sensitive potassium channels. This finding may be of clinical relevance because of the availability of potassium channel op eners, such as nicorandil, for human use.