Comparison of human growth hormone binding to rat liver plasma and Golgi membranes

The binding characteristics of hGH to Golgi and liver plasma membranes isolated from normal adult female rats have been compared to assess the biological differences between the Golgi and plasma membrane receptor. The effect of cations and the time course of binding were qualitatively similar for both Golgi and plasma membranes. The Golgi membranes from normal rats exhibited maximum binding at pH 6-7 compared to 5-6 for other membrane fractions. The highest apparent affinities (approx. 1 x 10(9) M-1) for hGH were observed in the light Golgi membranes from normal rats and the light and intermediate Golgi membranes from ethanol treated rats. The lowest apparent affinities (0.026 -0.1 x 10(9)M-1 if determined by competitive binding curves or 0.07 - 0.32 x 10(9)M-1 by Scatchard plots) for hGH were observed in plasma membranes isolated by either Neville's or Ray's method or a combination of both methods. The hGH receptors were determined to be lactogenic by competitive binding curves. The affinities of Golgi membranes were not affected by alterations in isolation procedures. Ethanol treatment of the rats prior to sacrifice and membrane isolation resulted in linear Scatchard plots for hGH binding to Golgi membranes compared to curved Scatchard plots for the Golgi membranes of normal rats. The marker enzyme activities of glucose-6-phosphatase and adenylate cyclase were lower in Golgi from ethanol treated rats while the galactosyl transferase activity increased in lighter golgi fractions from ethanol treated rats.