Insulin-induced receptor regulation in cultured Zajdela rat hepatoma cells and relationship to the stimulation of glycogen synthesis.

Insulin receptors were measured in cultured Zajdela rat hepatoma cells (ZHC cells), a stable cell line which presents differentiated hepatic functions. The number of sites was 50,000/cell at 2 C, and the dissociation constant for high affinity binding was 1.6 x 10(-10) M. Down-regulation of receptors occurred rapidly when cells were treated with insulin; this process was related to ambient insulin concentrations and led to a decrease in the number of insulin receptors from 50,000 to 30,000/cell. Cycloheximide prevented part of this regulation. When down-regulated cells were incubated in standard medium devoid of insulin, the number of receptor sites gradually increased and attained control values within 7 h; cyclohexamide inhibited this process. Insulin markedly enhanced glycogen synthesis in ZHC cells, with an ED50 of 1.0 x 10(-9) M, leading to an increase in the total cell glycogen content. In addition, the predicted righthand shift of the dose-response curve was observed for insulin-treated cells. These findings provide evidence of insulin-induced receptor regulation in cultured ZHC cells which is related to the biological effect of the hormone on glycogen synthesis.