Key result
Both S(+)- and R(-)-isomers of ketamine had equipotent cardiodepressant effects, identically decreasing contractile force, spontaneous beating rate, and transsarcolemmal Ca2+ current in guinea pigs.
Why the study?
Do ketamine isomers have differential effects on contractile force, spontaneous beating rate, and Ca2+ current in guinea pig cardiac preparations?
Do ketamine isomers have differential effects on contractile force, spontaneous beating rate, and Ca2+ current in guinea pig cardiac preparations?
The optical isomers of ketamine have equipotent cardiodepressant effects in guinea pig cardiac preparations, suggesting the more potent anesthetic S(+)-isomer could offer a clinical advantage by causing less cardiac impairment at equipotent anesthetic doses.
Answers are grounded in this paper and cite their sources.
Equipotent cardiodepressant effects of ketamine isomers in guinea pigs leave open whether S(+)-isomer offers cardiac advantage at equipotent anesthetic doses; human trials needed.
Ketamine possesses stereospecific actions of anesthesia with the S(+)-isomer being three to four times as potent an anesthetic as the R(-)-isomer. We investigated the mechanical and electrophysiologic effects of ketamine isomers in guinea pig cardiac preparations. Both isomers decreased the contractile force of electrically driven papillary muscles and the spontaneously beating rate of the right atria in a concentration-dependent manner. There were no significant differences between the S(+)- and R(-)-isomers for these measured variables. Consistent with the results from mechanical experiments, electrophysiologic experiments using whole cell voltage clamp techniques revealed that both isomers suppressed identically the transsarcolemmal Ca2+ current (I (Ca)), which plays a role in the generation of the force of contraction and the spontaneous firing of sinoatrial node cells. In conclusion, the optical isomers of ketamine have equipotent cardiodepressant effects in the guinea pig. Inasmuch as the S(+)-isomer is the more potent anesthetic, it could offer significant clinical advantage over the R(-)-isomer or the racemate, in terms of impairment of cardiac functions, if the present results could be extrapolated to the clinical setting. (Anesth Analg 1996;83:75-80)
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Sekino et al. (1996) studied Guinea pig cardiac preparations. S(+)-ketamine isomer vs. R(-)-ketamine isomer was evaluated on Contractile force, spontaneous beating rate, and transsarcolemmal Ca2+ current. Both S(+)- and R(-)-isomers of ketamine had equipotent cardiodepressant effects, identically decreasing contractile force, spontaneous beating rate, and transsarcolemmal Ca2+ current in guinea pigs.
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