EFFECTS OF HALOTHANE AND KETAMINE ON ACTIVATION AND INACTIVATION OF MYOCARDIAL CALCIUM CURRENT

We evaluated the effects of clinically relevant concentrations of halo thane (1%) and ketamine (10(-4)M) on activation, inactivation, and rec overy from inactivation of voltage-gated sarcolemmal calcium current ( I-Ca) in single guinea pig ventricular myocytes, using the whole cell voltage clamp. Both anesthetics had qualitatively similar effects. The potential at half-activation was shifted from -18 to -23 mV for halot hane (p < 0.03) and from -17 to -21 mV for ketamine (p = 0.005). There was no change in the slope of the activation curve for either anesthe tic. The potential at half-inactivation was shifted from -29 to -40 mV with exposure to halothane (p < 0.001) and from -27 to -33 mV (p < 0. 001) with exposure to ketamine. There was no change in the slope of th e inactivation curve with either agent. The changes in time constant o f recovery from steady-state inactivation with halothane did not reach statistical significance (178 vs. 207 ms, p = 0.20) and was significa ntly prolonged with exposure to ketamine (106 vs. 157 ms, p = 0.005). The two anesthetics show parallel shifts in activation, inactivation, and recovery from inactivation of I-Ca in ventricular myocardial cells . These findings in normal ventricular myocytes may help interpret the interactions of these anesthetics with other types of heart muscle, s uch as ischemic and immature myocardium.