Glucagon degradation in isolated rat hepatocytes: Effect of ammonium chloride and chloroquine

Abstract

It has recently been shown that, when [ 125I] glucagon is incubated with isolated rat hepatocytes at 37°, the radiolabelled material is progressively internalized by the cell and is found to associate preferentially with lysosome-like structures. To assess the role of this process in the degradation of the hormone, the degradation of [ 125I] glucagon by isolated rat hepatocytes was examined both in incubation media and in cell extracts, after exposure of the radiolabelled hormone to hepatocytes in the absence and in the presence of lysosomotropic agents NH 4Cl (8 mmoles/1) or chloroquine (10 μmoles/1); bacitracin (0.8 mg/ml i.e. 0.6 mmoles/1) was present in all experimental conditions to minimize extracellular degradation. Neither NH 4Cl nor chloroquine altered the time course and steady-state binding of [ 125I] glucagon, or the degradation of the hormone in incubation media. However, both agents partially inhibited the degradation of cell-associated [ 125I]glucagon in steady-state conditions. In dissociation experiments, NH 4Cl, and even more so chloroquine, decreased the rate and the extent of release of radiolabelled material from the cells. Moreover, after 60 min dissociation, the presence of either agent resulted in less degradation of both cell-associated [ 125I] glucagon and that released into the medium. These results suggest that lysosomes are involved in the intracellular degradation of glucagon.