Binding of insulin and nonsuppressible insulin-like activity to isolated perfused rat heart muscle: Evidence for two separate binding sites

Abstract

Binding of 125I-labeled insulin and 125I-labeled NSILA-S (nonsuppressible insulin-like activity-soluble) to isolated perfused rat heart muscle was found to be a specific and saturable process. Saturation of binding was reached with both substances at concentrations which maximally stimulate glucose uptake in heart muscle. Whereas unlabeled NSILA-S displaced 125I-labeled insulin, the reverse did not occur. 125I-labeled insulin and 125I-labeled NSILA-S showed different dissociation kinetics. The half-lives of dissociation of insulin and NSILA-S were 17 and 26 min, respectively. It is suggested that the plasma membrane of rat heart muscle possesses two separate receptors, one for insulin and another one for NSILA-S. NSILA-S shows also some affinity for the insulin receptor.