Trypsin-induced alterations of insulin binding, microfilament organization and cell shape in fibroblastic cultures from non-diabetic and diabetic mice

Abstract

Although fibroblastic cultures from the skin of both non-diabetic and diabetic (db/db) mice have specific receptors for insulin, cells from diabetic mice bind only half as much insulin as those from non-diabetic animals. Treatment of cultures from non-diabetic and diabetic mice with trypsin caused an increase in the total number of binding sites from 7.7 × 10 4 to 11.0 × 10 4 per cell in nondiabetic and from 2.9 × 10 4 to 5.1 × 10 4 per cell in diabetic cells. The increase is reversible and apparently specific for trypsin. Cells cultured from non-diabetic and diabetic animals are flat and fusiform and have microfilaments of various sizes occurring individually in the cytoplasm and in bundles running parallel with the plasma membrane. Trypsin treatment causes rounding of cells, with development of numerous blebs and folds, and depolymerization and disappearance of microfilament bundles in both non-diabetic and diabetic cells. The present study demonstrates that although diabetic fibroblasts have fewer insulin receptors than cells from non-diabetic littermates, the effects of trypsin on insulin receptors, organization of macrofilament bundles, and cell morphology have not been altered by the expression of the diabetic state.