Effects of high glucose on the hypoxic isolated guinea pig heart: interactions with ATP-dependent K+ channels?

The effect of perfusion with elevated glucose concentrations on hypoxic myo cardium was investigated in isolated Langendorff guinea pig hearts. For tha t purpose, mechanical (heart rate, systolic peak pressure and coronary flow ) and electrophysiological (monophasic action potential duration = MAP, ect opic beats) data were evaluated. At the end of the experiments the hearts w ere examined histologically after trypan blue vital staining for quantifica tion of irreversible myocardial damage. In the absence of insulin moderate glucose elevation (from 5 to 15 mM) exerted beneficial effects on hypoxic h earts: the depressed contraction was improved, the action potential shorten ing partly reversed and the percentage of irreversibly damaged myocytes dim inished. Glucose did not have any effect on heart rate and arrhythmias unde r hypoxia or reperfusion. A contribution of cardiac ATP-dependent K+ channe ls to the effects of glucose could be excluded by further experiments. Thus , blocking these channels with high glibenclamide concentrations did not af fect the action of glucose on MAP and contraction. To some degree the gluco se effect on MAP, but not on systolic pressure, was also observable under n ormoxic conditions. (C) 1999 Elsevier Science B.V. All rights reserved.