Effect of sodium on 3Hethylketocyclazocine binding to opioid receptors in frog brain membranes

摘要

The specific binding of (3H)ethylketocyclazocine to frog brain membrane preparation was enhanced in the presence of sodium ions administered as NaCl, both at 0 °C and at room temperature. The optimal NaCl concentration was 25 mM at 0 °C and 50 mM at 24 °C. MgCl2inhibited the 3Hethylketocyclazocine binding. Two binding sites (high and low affinity) were established with 3Hethylketocyclazocine as ligand by equilibrium binding studies. Addition of NaCl increased the Bmaxof the low-affinity site more than that of the high-affinity site at both temperatures. Affinities were higher at 0 °C than at 24 °C. TheKDvalues were not significantly influenced by sodium ions. The dissimilarities between the rat and frog brain opioid receptors in 3Hethylketocyclazocine binding are attributed to the different lipid composition of the two membr