Immunologic similarity of insulin receptors in Golgi and plasma membranes from rat liver.

Insulin receptor antibodies (IRA) have been shown to inhibit 125I-labeled insulin binding to plasmalemma and whole cells. An earlier study claimed that IRA was less able to inhibit 125I-labeled insulin binding to intracellular receptors than plasmalemma of rat liver. We have examined the effect of IRA serum from a patient with insulin-resistant diabetes mellitus on 125I-labeled insulin binding to plasmalemma and Golgi fractions prepared from female rat liver. Maximum inhibitions of 125I-labeled insulin binding were 44, 48, 55, and 51% for plasmalemma, Golgi light, Golgi intermediate, and Golgi heavy, respectively, and these were maintained at a serum dilution of up to 1:100. Half-maximal inhibition occurred at a serum dilution of 1:900. The IRA serum had no inhibitory effect on 125I-labeled ILAs and ovine prolactin (oPRL) binding to either plasma membrane or Golgi fractions. Analysis of the effect of the IRA serum showed that its inhibition of 125I-labeled insulin binding linearized the Scatchard plot, with abolition of the high affinity portion of the curve, and reduced the number of low affinity sites. The affinity of binding to Golgi but not plasmalemma insulin receptors was decreased. We conclude that there is immunologic similarity between intracellular and cell surface insulin receptors of rat liver. This is compatible with a fairly rapid equilibration between these two receptor populations, as expected with an active membrane recycling process.