Insulin receptor downregulation in isolated hepatocytes of river lamprey (Lampetra fluviatilis).

Insulin receptor downregulation in the isolated hepatocytes of lamprey (Lampetra fluviatilis) was studied at the ambient temperature for this species. Preincubation of hepatocytes with 10(-9)-10(-8) M unlabeled insulin decreased insulin binding capacity to 43, 37, and 34% at 4, 15, and 25 degrees, respectively. Preincubation of hepatocytes in the presence of 10(-10) M unlabeled insulin had no effect on the 125I-insulin binding. The maximal decrease in the 125I-insulin binding was reached after 10 min of preincubation and was then maintained at a constant level for 2 hr. Competitive binding assays demonstrated that preincubation with unlabeled insulin resulted in a 45% decline in the number of binding sites. In rat adipocytes and frog hepatocytes used for the comparison, preincubation with insulin caused a 65% decrease in cell-surface receptors, while intracellular (internalized receptors) increased proportionally. In contrast, in the lamprey hepatocytes both cell-surface and intracellular receptors decreased. We conclude that insulin receptors of the lamprey hepatocytes could be down-regulated at the ambient temperature for the species and at the physiological concentrations of insulin (10(-9)-10(-8) M).