SODIUM-CALCIUM EXCHANGE IN NEONATAL MYOCARDIUM - REVERSIBLE INHIBITION BY HALOTHANE

Neonatal myocardium is distinctly more sensitive to extracellular calc ium levels than is mature myocardium. This has been ascribed to the po orly developed sarcoplasmic reticulum of neonatal myocardium. Recent e vidence has suggested that there is an increased dependence of neonata l myocardium on the sodium-calcium exchange current, and that sodium-c alcium exchange may be a major source of calcium influx in neonatal my ocardial cells. We determined the effect of halothane on the sodium-ca lcium exchange current on single neonatal (2- to 5-day-old) rabbit ven tricular myocytes by means of the whole cell voltage clamp. Lower (1.5 %) halothane decreased sodium-calcium exchange current by 49%, from 29 +/- 3 to 15 +/- 6 pA. Higher (3%) halothane decreased this current by 66%, from 50 +/- 9 to 17 +/- 9 pA. Thus halothane has a reversible in hibition of sodium-calcium exchange current in neonatal myocardium. In hibition of sodium-calcium exchange current would be expected to have a magnified effect on contractility in neonatal as opposed to adult my ocardium, and could theoretically ameliorate reperfusion injury due to influx of calcium via the sodium-calcium exchanger.