Tunicamycin sensitivity of prolactin, insulin and epidermal growth factor receptors in rat liver plasmalemma.

We have used the glycosylation inhibitor tunicamycin to assess the stability of the receptors for prolactin, insulin and epidermal growth factor (EGF) in rat liver cell membrane. Direct binding studies on liver plasmalemma fractions which were isolated from tunicamycin-treated rats revealed a rapid loss of prolactin receptors (t1/2 approximately 35 min) with a more prolonged half-life for insulin (10 h) and EGF receptors (8 h). The rates of receptor loss were similar to the respective half-lives of the receptors as documented by others using cultured cells. The respective ligands for each receptor were lost more rapidly from liver, i.e. prolactin, t1/2 approximately 10 min, insulin, t1/2 approximately 5 min and EGF, t1/2 approximately 17 min. Previous studies have shown ligand loss in vivo to be receptor mediated. Thus, receptors and their ligands do not turn over synchronously in vivo. These studies also point to a major role for N-linked oligosaccharide side chains in the functional insertion of prolactin, insulin and EGF receptors into the hepatocyte cell surface in vivo.