Na(+)-Ca2+ exchange influences halothane and caffeine contractures of malignant hyperthermic skeletal muscle.

These experiments sought to determine the influence of sarcolemmal Na(+)-Ca2+ exchange on halothane and on caffeine contractures of malignant hyperthermic (MH) skeletal muscle. Fiber bundles excised from MH susceptible pigs (Pietrain) were exposed to halothane (3%) and caffeine (0.5-8.0mM) while Na(+)-Ca2+ exchange was inhibited by reducing extracellular Na+ from 100% to 50, 25 and 0% of control. Halothane contracture magnitude was not altered by 50 or 25% Na+ whereas 0% Na+ increased the contractures by 51%. 0 and 25% Na+ increased the magnitude of caffeine contractures (2-8mM) by 53-176%. These results suggest that external Na+ and the Na(+)-Ca2+ exchange mechanism influences contractures of MH skeletal muscle.