Halothane, enflurane, and isoflurane decrease calcium sensitivity and maximal force in detergent-treated rat cardiac fibers.

This study was designed to test the hypothesis that the volatile anesthetics directly affect cardiac contractile proteins. For this purpose, the effects of various anesthetic doses of halothane, enflurane, and isoflurane on myocardial calcium sensitivity and maximal calcium-activated force were examined in rat cardiac fibers skinned with Triton X-100. In this preparation, all membranes are chemically destroyed, and the sarcoplasmic reticulum is not functional. The three anesthetics shifted the pCa/tension curves (pCa = -log10[Ca2+]) toward higher calcium concentrations and decreased pCa for half-maximum activation (pCa50) in a dose-dependent and reversible fashion without changing the slope of this relationship (Hill coefficient). No differences between agents were observed at equipotent anesthetic concentrations. In addition, the three anesthetics decreased both maximal activated tension and tension at half-maximal activation in a dose-dependent fashion. Both the decrease in calcium sensitivity and the decrease in maximum activated tension may contribute to the negative inotropic effects of these agents. The relative importance of such effects compared with the other mechanisms of action remains to be determined, however.