Evidence for two insulin receptor populations on human erythrocytes

Abstract

Human erythrocytes specifically bind ¹²⁵I-insulin in a manner similar to cells in which insulin exerts a physiological response¹. In addition, erythrocytes are of practical value for correlating in vitro insulin binding with in vivo carbohydrate intolerance^2,3. The competitive binding of labelled and unlabelled insulin to erythrocyte receptors is typically curvilinear when plotted according to Scatchard⁴. The curvilinear nature of the Scatchard plot describing insulin binding to membrane receptors, although originally attributed to heterogeneous sites⁵, has been more recently interpreted as negative cooperativity between homogeneous sites⁶. Evidence reported here, however, suggests that there are two populations of insulin receptors on erythrocytes. Specific concentrations of concanavalin A (Con A), a lectin which mimics insulin activity⁷, are shown here to inhibit one population of receptors leaving another population unaffected.