Negative Inotropic Effect of Ketamine in Rabbit Ventricular Muscle

The effect of ketamine on myocardial contractile force was examined in rabbit papillay muscles in order to determine the underlying mechanism of action of the anesthetic. Ketamine HCl (20 and 40 mg/L) inhibited rested-state contractions that are dependent on the transsarcolemmal influx of Ca for activation and reduced the upstroke velocity of the slow action potential, which reflects Ca influx through the slow Ca channel. On the other hand, ketamine had a relatively small effect on potentiated-state contractions and no effect on rapid cooling induced contractures, both of which are activated by the release of Ca stored in the sarcoplasmic reticulum. These results suggest that ketamine inhibition of transsarcolemmal Ca influx plays a major role in the negative inotropic action of the anesthetic.