Modulation of insulin receptors in cultured adipocytes as studied by a latex minibead probe

In monolayer cultures, adipocytes transform into spindle-shaped cells, morphologically similar to buccal submucosa-derived fibroblasts. Insulin receptors were searched for on the surface of these cells using a visual probe which consisted of latex minibeads covalently bound to insulin. Adipocyte-derived cells showed clusters of insulin receptors not observed on the surface of fibroblasts derived from submucosa. The finding indicates that despite their fibroblastic morphology and the loss of their lipid inclusions in culture, these adipocytes do not lose their state of differentiation and therefore should be considered lipid-depleted adipocytes rather than fibroblasts. Moreover, quantitative analysis demonstrated a significant increase in the number of insulin receptors in cultured cells as compared to isolated but not cultured cells. This may reflect the low concentration of insulin in the culture medium as compared to the in vivo environment and indicates that the cells are subject to regulatory mechanisms of adipocytes.