Opposite effects of halothane on guinea-pig ventricular action potential duration

Halothane protects the heart against the reperfusion injury observed after an ischemia. In ischemic or anoxic conditions, a large ATP-sensitive K+ (K- ATP) conductance is supposed to provide an endogenous protection to the myo cardium. In this study, we tested the possibility that halothane acted by m odulating this conductance. Isolated guinea-pig cardiomyocytes were success ively studied in current clamp and in voltage-clamp conditions. Action pote ntials regulation by halothane was tested in control conditions and in situ ations where the K-ATP channels were activated. In control conditions, halo thane decreased action potential duration of myocytes but did not significa ntly alter the inward rectifying K+ current. Conversely, halothane lengthen ed action potential of cells in which the K-ATP conductance was activated, by inhibiting the K-ATP current. In ischemic conditions, simultaneous short ening of long action potentials and lengthening of shortened ones would be expected to homogenize the absolute refractory period at the border between normoxic and anoxic zones. This effect, together with a decrease in calciu m load, could protect the myocardium against re-entrant arrhythmias. (C) 20 00 Elsevier Science B.V. All rights reserved.