INCREASED INSULIN-RECEPTOR NUMBER AND INSULIN RESPONSIVENESS IN A CHICKEN HEPATOMA-CELL LINE

Insulin receptor number and insulin responsiveness were compared in a chicken hepatoma cell line (LMH) and in normal chicken hepatocyte (cHe p) cells cultured in the same conditions. LMH cells expressed two- to threefold more insulin receptors than cHep cells, without significant changes in affinity. The tyrosine kinase activity of solubilized and l ectin (lentil+wheat germ agglutinin; WGA)-purified LMH receptors was h igher than that of cHep receptors. The ATP hydrolytic activity previou sly observed in WGA-purified receptors from chicken Liver membranes wa s also present in WGA-purified receptors from cultured cHep cells. Thi s unidentified membrane-associated ATPase was absent from LMH membrane -solubilized material and therefore from WGA-purified LMH insulin rece ptors. Finally, LMH cells incorporated at least tenfold more amino iso butyric acid than cHep cells in the absence of insulin and were more r esponsive to insulin. The enhanced basal amino acid transport of LMH c ells was most probably the consequence of their proliferative activity . The enhanced insulin responsiveness of LMH cells can be accounted fo r, at least in part, by one or several of the modifications presently demonstrated in LMH cells when compared with normal cultured hepatocyt es: increased insulin receptor number and tyrosine kinase activity and possibly the loss of the membrane-associated ATPase.