Myocardial depression by nitrous oxide and its reversal by Ca++

The effects of 50 per cent nitrous oxide on isometric contractile force of electrically stimulated cat papillary muscle suspended in a Tris-buffered solution at five concentrations of Ca++ ranging from 1 to 15 mM were studied. Compared with an equal concentration of nitrogen, or with pure oxygen, nitrous oxide caused a highly significant reduction in contractile force, averaging 22 per cent at 2.5 mM Ca++. This reduction in force, like that caused by halothane, could be antagonized by increasing [Ca++] in the bathing medium. However, the reductions in force caused by equinarcotic concentrations of halothane and nitrous oxide are significantly different in magnitude, suggesting that the mechanisms of anesthetic action in the central nervous system and in the myocardium may not be the same.