Characteristics of human erythrocyte insulin receptors

Abstract

Highly specific insulin receptors were identified on human erythrocytes. A modification of the monocyte insulin radioreceptor technique permitted distinct separation of human erythrocytes with their bound insulin from the free insulin. When incubated with 80 pg/ml of 125I-insulin (pH 8.0, 3.5 h, 15.degree. C), erythrocytes from 17 normal volunteers specifically bound 10% (.+-. 1.450 SD) of the total 125I-insulin. Less than 15% the total 125I-insulin bound was nonspecific. Binding of 125I-insulin to human erythrocytes was dependent on pH and temperature. Less than 5% of the insulin available to the plasma membrane was degraded. Both Ca and Mg enhanced 125I-insulin binding by 100% but had no synergistic effect when mixed in a 1:1 molar ratio. Scatchard analysis of the binding data resulted in a curvilinear plot with characteristics typical of negative cooperative interactions between receptor sites and with an unoccupied site affinity constant of 0.1 .times. 108 M-1. Human erythrocytes have 2000 insulin binding sites per erythrocyte with 14 sites/.mu.m2 of surface area. The readily available human erythrocyte has both specific insulin binding sites and binding characteristics similar to other human cell types. These studies provided the basis for further clinical investigation of polypeptide hormone receptors on human erythrocytes.