Characteristics of the Human Lymphocyte Insulin Receptor

Abstract Insulin interactions with human lymphocytes in established cultures and with isolated peripheral lymphocytes have been studied using 125I-insulin. Receptors in circulating lymphocytes are indistinguishable from those found in cultured cells, and the lymphocyte receptors show striking similarities to those structures described in fat cell and liver preparations. In lymphocytes, the ability of insulin or insulin analogues to inhibit binding of 125I-insulin is directly proportional to the ability of that preparation to inhibit binding of labeled hormone to purified liver membranes or to stimulate glucose oxidation in the fat cell. Binding of 125I-insulin to lymphocytes is a rapid and reversible process. Binding is maximal at 15°. Dissociation rate studies revealed a biphasic curve and the constants obtained were 8.3 x 10-5 s-1 and 8.3 x 10-4 s-1. The apparent affinity constants of the two orders of binding sites in the cultured lymphocytes were 1.2 x 1010 m-1 and 1.1 x 109 m-1, whereas in the normal circulating lymphocytes the values were 2.0 x 109 m-1 and 1.4 x 108 m-1. At 30° there is very little degradation of labeled insulin by lymphocytes, and at 15° there is no detectable degradation with cultured or circulating cells. Binding of 125I-insulin to cultured lymphocytes is unaffected by Ca++, Mg++, or EDTA. The optimum pH for binding occurs at about 7.8. Insulin binding to cells is unaffected by digestion with DNase, RNase, or neuraminidase. However, tryptic digestion destroys the capacity of the cells to bind insulin.