The effect of diet on ouabain binding to erythrocytes from obese subjects

Ouabain binding to erythrocyte membranes is increased in obese subjects. Three study groups are compared: 14 reference subjects, 102 +/- 16% of ideal weight; 9 obese on unrestricted diets, 207 +/- 16% of ideal weight; 11 obese on restricted diets, 202 +/- 35% of ideal weight. A reproducible (CV = 11.3%) ouabain-binding assay is used to measure Na+-K+ ATPase sites in erythrocyte membranes. The number of binding sites per red blood cell for obese subjects on unrestricted diets, 431 +/- 30, is greater than for the reference group, 346 +/- 66 (p less than 0.01), or for obese subjects on restricted diets, 371 +/- 68 (p less than 0.05). These data suggest that caloric intake influences the number of Na+-K+ ATPase sites. Scatchard plots indicate only one type of binding site for ouabain with an affinity constant of about 3 X 10(8) M-1.