Binding, internalization, and degradation of [125I]insulin by cultured bovine aortic endothelial cells: Effects of serotonin

Cultured bovine aortic endothelial cells bind and internalize[125I]insulin and down regulate insulin receptors. Internalized insulin was not degraded significantly and diffused from the endothelial cells. Neither 5-hydroxytryptamine, methylamine, nor dansyl-cadaverine have any observable effect on insulin binding, internalization, metabolism, or down regulation of insulin receptors. Transglutaminase activity, however, is inhibited by 5-hydroxytryptamine and methylamine. These data indicate that transglutaminase is not required for insulin receptor-mediated endocytosis by bovine aortic endothelial cells in culture.