Redistribution of ¹²⁵I-Insulin on the Surface of Rat Hepatocytes as a Function of Dissociation Time

In the present experiments, we have correlated the distribution of ¹²⁵I-insulin on the surface of rat hepatocytes with the dissociation of ¹²⁵I-insulin from the cell. When ¹²⁵I-insulin interacts with isolated rat hepatocytes at 15°C, an increasing proportion of the bound ligand becomes nondissociable under the influence of acid pH (6.0), trypsin (0.5 mg/ml), or an excess of unlabeled insulin (10⁻⁶ M). Under these conditions, only a small percentage of the labeled material is internalized as determined by quantitative electron microscope (EM) autoradiography. This progressive nondissociability of the ligand parallels its movement from microvilli to coated pits and its progressive concentration in these later surface specializations. These data suggest that receptors in different domains of the plasma membrane may have different dissociation rates for the ligand.