Effects of nitrous oxide on contractility, relaxation and the intracellular calcium transient of isolated mammalian ventricular myocardium.

The effects of nitrous oxide on variables of contractility and relaxation were analyzed in isolated ferret right ventricular papillary muscles. Each mechanical variable, in isometric, isotonic, and zero-load-clamped twitches, was compared to the average value of that variable in control conditions (50% nitrogen in oxygen), before and after equilibration with 20%, 30% and 50% nitrous oxide in 50% oxygen. Nitrous oxide caused a concentration-dependent decrease in contractility under all loading conditions, with minor changes in relaxation. The intracellular calcium transient was detected with the Ca(++)-regulated photoprotein aequorin. The change in aequorin luminescence on exposure to nitrous oxide suggests that the negative inotropic effect of nitrous oxide is due to a decrease in calcium availability with no effect on myofibrillar responsiveness to calcium.