Reduced activity of the red-cell sodium-potassium pump in human obesity.

Looking for evidence of reduced energy use in the cells of obese persons, we measured the numbers of sodium-potassium-pump units in erythrocytes from a group of 21 obese human subjects and found them to be reduced by 22 per cent as compared with those of nonobese controls (P <0.001). The cation-transport activity of the pump, as measured by 86rubidium uptake by the cells, we also reduced in parallel with decrease in pump units. An increased concentration of sodium in the red cells of obese subjectes was also found (9.6 +/- 0.7 vs. 7.1 +/- 0.6 mmol per liter of cells; P<0.01). This finding demonstrates independently the physiologic importance of reduced numbers of sodium-pump units and reduced pump activity as measured by ouabain binding and rubidium transport, respectively. The magnitude of the reduction in the number of pump units was found to be negatively correlated with the percentage of ideal body weight (r = 0.56, P<0.001); this observation suggests a possible role of abnormalities of the sodium pump in the pathophysiology of obesity.