Insulin Receptors in Cultured Human Fibroblasts

In order to study human insulin resistance, we have first characterized the interaction of insulin with specific insulin receptors in cultures of normal human fibroblasts. ¹²⁵I-insulin bound rapidly to human fibroblasts in suspension at 15°, achieving steady state between one and three hours. Insulin was not degraded during the binding assays. In competitive binding experiments, 2 ng/ml. (3.3 × 10⁻¹⁰ M) of unlabeled insulin reduced ¹²⁵I-insulin binding by 50 per cent. Insulin analogues competed for binding in proportion to their biologic potencies. A curvilinear Scatchard plot was obtained, suggesting the existence of negatively cooperative site-site interactions among the insulin receptors. This was confirmed directly by studies of the dissociation kinetics. The high affinity, specificity, and negative cooperativity of the fibroblast insulin receptor closely resembles the properties of other human insulin receptors. The cultuted human fibroblast should prove a useful tissue for the study of insulin-resistant states in man.