No correlation between erythrocyte Na,K-ATPase activity and resting metabolic rate in humans

The relationship between erythrocyte Na,K-ATPase activity (ouabain-inhibited 86Rb uptake) and metabolic efficiency (defined as the resting metabolic rate adjusted for body composition) was examined in 31 healthy young subjects (16 men and 15 women, 19-33 yr old). Mean (+/- SEM) Na,K-ATPase activity (expressed as nanomoles of Rb taken up per h/billion erythrocytes) was similar in the men (86 +/- 3) and women (94 +/- 7). After adjusting metabolic rate for body cell mass (total body potassium), men and women had similar metabolic rates, and subjects with the highest percent body fat tended to have the highest metabolic rates. Ouabain-sensitive erythrocyte Rb uptake was related to less than 2% of the variability in resting metabolic rate after adjusting metabolic rate for differences in body composition. Erythrocyte Na,K-ATPase activity does not appear to be a useful marker of metabolic efficiency in man.