A microcalorimetric study of the sodium-potassium-pump and thermogenesis in human skeletal muscle

Thermogenesis in human skeletal muscle was monitored by measurement of heat production using perfusion microcalorimetry. Heat production significantly correlated with relative body weight. The energy expenditure of the Na-K-pump (delta P), assessed after inhibition by ouabain in Krebs-Ringer phosphate buffer containing glucose and insulin, amounted to 6% of the total heat production in vastus lateralis muscle. Muscle potassium positively correlated with delta P (r = 0.84, P less than 0.005). For rectus abdominis muscle delta P was 8-15%; 95% confidence interval for the difference was 3-5% when comparison was made with vastus lateralis. The finding of a positive relationship between delta P and muscle magnesium (r = 0.68, P less than 0.04) is possibly explained by the dependence of ATP hydrolysis on internal magnesium. Our data on resting thermogenesis in small muscle samples agree to previous estimates of O2 consumption in human skeletal muscle in vivo.