Reciprocal changes of insulin and glucagon receptors in primary cultured hepatocytes

The specific [125I]insulin binding to primary cultured hepatocytes was significantly greater than that to freshly isolated hepatocytes. Low affinity insulin binding sites in cultured cells were 6-fold greater in number than those of freshly isolated cells without a significant change in high affinity sites. However, both sensitivity (insulin concentration for half maximum stimulation) and responsiveness (% of increase above the basal level) to insulin for the stimulation of ODC activity were similar for isolated and cultured cells indicating an important role of high affinity sites in the insulin action. On the other hand, the specific [125I]glucagon binding to cultured cells was significantly decreased. Low affinity glucagon binding sites in cultured cells decreased by about 50% in cultured cells without a significant change in high affinity sites. Both sensitivity and responsiveness to glucagon for the stimulation of ketogenesis from palmitate also decreased as compared with those of isolated cells, indicating an important role of low affinity sites in the glucagon action. These results indicate that insulin and glucagon receptors were reciprocally changed in cultured cells, as compared with isolated cells.