EFFECTS OF SEVOFLURANE, ISOFLURANE, AND HALOTHANE ON MECHANICAL AND ELECTROPHYSIOLOGIC PROPERTIES OF CANINE MYOCARDIUM

We studied the effects of sevoflurane on contraction and membrane potentials in isolated canine ventricular muscle strips. Sevoflurane (>0.5%) depressed electrically induced contraction in a dose-dependent manner. Moreover, sevoflurane did not show stimulation frequency-dependent depression in contraction as shown with local anesthetics. The inhibitory effect was more pronounced in high-K+ Tyrode's solution than in normal Tyrode's solution, suggesting that sevoflurane may inhibit transmembrane Ca2+ influx. In contrast, isoflurane and halothane were equally effective in depressing electrically induced contractions in normal and high-K+ Tyrode's solution. In electrophysiologic experiments, sevoflurane at higher concentrations (>2.0%) depressed both overshoot and the plateau phase of the action potentials. These depressant effects were more pronounced in high-K+ Tyrode's solution. Resting membrane potential was not affected by sevoflurane. We conclude that depression of myocardial contractility by sevoflurane may be due to a block of the transmembrane calcium influx.