Effects of sevoflurane on the intracellular Ca2+ transient in ferret cardiac muscle

Background: Sevoflurane depresses myocardial contractility by decreasing transsarcolemmal Ca2+ influx. In skinned muscle fibers, sevoflurane affects actin-myosin cross-bridge cycling, which might contribute to the negative inotropic effect. It is uncertain to what extent decreases in Ca2+ sensitivity of the contractile proteins play a role in the negative inotropic effect of sevoflurane in intact cardiac muscle tissue. The aim of this study was to assess whether sevoflurane decreases myofibrillar Ca2+ sensitivity in intact living cardiac fibers and to quantify the relative importance of changes in myofibrillar Ca2+ sensitivity versus changes in myoplasmic Ca2+ availability by sevoflurane. Methods: The effects of sevoflurane 0-4.05% vol/vol (0-1.5 minimum alveolar concentration [MAC]) on isometric and isotonic variables of contractility and on the intracellular calcium transient were assessed in isolated ferret right ventricular papillary muscles microinjected with the Ca2+-regulated photoprotein aequorin. The Intracellular calcium transient was analyzed in the context of a multicompartment model of intracellular Ca2+ buffers in mammalian ventricular myocardium. Results: Sevoflurane decreased contractility, time to peak force, time to half isometric relaxation, and the [Ca2+](i) transient in a reversible, concentration-dependent manner. Increasing [Ca2+](o) in the presence of sevoflurane to produce peak force equal to control increased intracellular Ca2+ transient higher than control. Conclusions: Sevoflurane decreases myoplasmic Ca2+ availability and myofibrillar Ca2+ sensitivity in equal proportions except at 4.05% vol/vol (1.5 MAC), where Ca2+ availability is decreased more. These changes are at the basis of the negative inotropic effect of sevoflurane in mammalian ventricular myocardium.