Internalization of colloidal gold-labelled insulin complexes into cultivated human smooth muscle cells

The binding and internalization of colloidal gold-labelled insulin complexes into cultivated human arterial smooth muscle cells was studied. We could demonstrate that the colloidal gold-labelled insulin complex was bound to specific receptors on the cell surface of smooth muscle cells and internalized after 30 min at 20 degrees C. The gold-labelled insulin complexes entered the cell via vesicles and escaped from them in the cytoplasm. The biological activity of the complexes was determined by measuring their effect on DNA synthesis in smooth muscle cells and incorporation of (14C)-glucose into isolated fat cells. The binding characteristics of the complexes were examined by competitive inhibition of 125I-insulin binding to isolated fat cells in the presence of increasing concentrations of gold-labelled insulin complexes or unlabelled insulin. The gold-labelled insulin complex showed a growth promoting and metabolic effect and was able to compete with 125I-insulin for its binding sites.