Heterogeneous effects of inhibitors of receptor processing on insulin binding and intracellular accumulation in...

This study utilized uniform incubation conditions and demonstrated heterogeneity in the effects of various agents on 125-insulin binding and intracellular accumulation in five cell types. The cells used in this study included rat adipocytes, H4IIEC3 cultured hepatoma cells, normal human fibroblasts, and 3T3-L1 preadipocytes and adipocytes. Bacitracin increased insulin binding to rat adipocytes but inhibited binding to all other cells. Chloroquine increased total cell-associated insulin in all cells except H4IIEC3 hepatoma cells. Methylamine and dansylcadaverine increased or decreased binding depending on cell type. Similar heterogeneity was found in the intracellular accumulation of insulin. Under control conditions, intracellular insulin at steady state varied from 16 to 52% of the total cell-associated insulin. Bacitracin decreased intracellular accumulation of insulin in 3T3-L1 adipocytes, preadipocytes, and human fibroblasts but increased accumulation in rat adipocytes. Chloroquine increased insulin accumulation in all cell types except H411EC3 hepatoma cells. Both methylamine and dansylcadaverine increased intracellular insulin in rat adipocytes and decreased accumulation in human fibroblasts. These results provide additional evidence of heterogeneity in insulin and/or insulin receptor processing among different cell types.