Effect of fasting on insulin binding to hepatocytes and liver plasma membranes from rats.

Binding of [125I]iodoinsulin to isolated hepatocytes from fed and fasted rats was measured. Hepatocytes from fed rats bound significanlty more [125I]iodoinsulin at insulin concentrations ranging from 0.15--100 nM. Scatchard and average affinity profile data analyses showed no significant difference in the affinities of the binding sites but indicated a decrease in the receptor concentration of the hepatocytes from fasted rats. In contrast to hepatocytes, liver plasma membranes of fasted rats showed increased insulin binding at all insulin concentrations, except the highest level of 100 nM. Analysis of the data indicated a significant increase in the affinity of the receptors but no change in the receptor concentration. Evidence is presented that the differences in the results obtained with hepatocytes and membranes were not due to the differences in the recovery of the plasma membranes. The results suggest that insulin binding by intact hepatocytes does not necessarily reflect the receptor protein content of the cell membrane and that the liver cell modulates its response to insulin by changes in the architecture of the plasma membrane.