Insulin receptors in Zajdela rat ascites hepatoma cells and their sensitivity to certain enzymes and lectins.

The insulin receptors in two strains of Zajdela ascites hepatoma cells have been studied. Specific binding of insulin was investigated at 4,15, and 22°,and the amount of insulin bound at steady state was proportional to the cell concentration. The optimum pH was 7.6. Scatchard analysis of the insulin binding exhibited cur vilinear plots. The number of insulin receptors was mark edly reduced in Zajdela D and H cells as compared to normal hepatocytes. Furthermore, the estimated number of sites was much lower in Zajdela D hepatoma, the most transplanted tumor, compared to Zajdela H hepatoma. The dissociation constants were not modified by the transformation. Dissociation experiments have revealed enhancement of the dissociation rate of bound '"(-labeled insulin by native insulin. Trypsin and papain digestion of Zajdela cells led to a marked inhibition of insulin binding. After digestion with glycosidases, sialidase, and/or galactosidase, the insulin binding was not decreased. The specific binding of insulin to cells was diminished after pretreatment of Zajdela cells with concanavalin A. Scatchard analysis of insulin binding indicated that low concentrations of the lectin inhibited especially high-affin ity sites. Preincubation of the cells with wheat germ agglutinin or the lectin Sophora japÃ3nica resulted in a biphasic effect on insulin binding. Thus, the Zajdela D and H ascites hepatoma cells present a decreased number of specific insulin receptors compared to normal cells, this number being much lower in the most transplanted tumor.