Comparison of human erythrocyte insulin binding and adenosinetriphosphatase activity

Twelve healthy, non-obese male volunteers were selected to measure cellular magnesium (Mg(++)), calcium (Ca(++)), sodium/potassium (Na(+)/K(+)), and adenosinetriphosphatase (ATPase) activities. Measurements were performed using a crude hemolysate as well as a membrane fraction representing cytosolic pump activity. Binding-site data were subjected to Scatchard analysis for determination of receptor number and affinity.There were 432 ± 1.87 insulin-binding sites per cell. ATPase activity was measured in units of moles of inorganic phosphate (Pi) released per gram of hemoglobin (Hgb) every two hours (μmol of Pi/g of Hgb/2 h). Na(+)/K(+)-ATPase activity in the hemolysate and membrane fractions was 18 ± 0.99 μmol of Pi/g of Hgb/2 h and 11.0 ± 0.88 μmol of Pi/g of Hgb/2 h, respectively. Calcium-ATPase activity was 136 ± 1.92 μmol of Pi/g of Hgb/2 h in the hemolysate, and 82 ± 2.07 μmol of Pi/g of Hgb/2 h in the membrane. Magnesium-ATPase activity in these fractions measured 24 ± 1.09 and 16 ± 0.91, respectively.Linear regression analysis of binding capability vs pump activity failed to disclose a significant relationship. Given the narrow range of values in this small study group, a much larger sample size will be required before a relationship can be established.