EFFECTS OF HALOTHANE AND ISOFLURANE ON RAT VENTRICULAR ACTION-POTENTIALS RECORDED IN-SITU

The effects of halothane and isoflurane on ventricular intracellular a ction potentials recorded in situ in pentobarbital anesthetized rats w ere studied. Halothane (0.5, 1 and 2 vol.%) and isoflurane (0.75, 1.5 and 3 vol.%) did not have identical effects on rat epicardial action p otentials recorded by floating microelectrodes. However, over the conc entration range tested, both anesthetics reduced blood pressure and he art rate to a similar extent. Isoflurane did not effect the maximum ra te of rise of the action potential or action potential amplitude. Howe ver, 3 vol.% isoflurane reduced the resting membrane potential from -7 2+/-2 to -65+/-3 mV (mean+/-SEM, p<0.05) while the highest concentrati on of halothane had no effect. Halothane (2 vol.%) reduced action pote ntial amplitude from 74+/-4 to 65+/-3 mV (p<0.05) and reduced the maxi mum rise rate of the action potential from 175+/-21 to 133+/-8 V/s (p< 0.05). Both isoflurane and halothane prolonged action potential durati on at 10, 25 and 50% repolarization while only halothane significantly shortened action potential duration at 75% repolarization. Thus the e ffects of halothane and isoflurane on ventricular transmembrane action potentials were similar, but not identical. The relevance of such obs ervations to the antiarrhythmic actions of halothane, but not isoflura ne, in this species is not clear.