Size of Vasopressin Receptors from Rat Liver and Kidney

Specific vasopressin receptors in rat liver membranes were recently characterized [Cantau et al., Journal of Receptors Research , in the press]. They differ from the receptors characterized earlier in kidney membranes as regards coupling with adenylate cyclase and specificity towards vasopressin structural analogues [Rajerison et al. (1974) J. Biol. Chem. 249 , 6390–6400; Butlen et al. (1978) Mol. Pharmacol. 14 , 1006–1017]. The object of the present work was to see whether these differences reflect a difference in the molecular size of liver and kidney vasopressin receptors. For this purpose, rat liver and kidney membranes were incubated with [ 3 H]vasopressin and solubilized with Triton X‐100 (0.3%). The properties of the macromolecular components of soluble extracts to which labelled vasopressin remained bound were observed to resemble those of the intact membrane receptors as regards binding reversibility at 30–37° C and sensitivity to guanyl nucleotides. The hydrodynamic parameters of the soluble hormone‐receptor complexes were estimated from Ultrogel column filtration experiments and from sucrose density gradient ultracentrifugation experiments. The following values were obtained for liver and kidney receptors respectively: Stokes' radii: 5.4 and 5.6 nm; standard sedimentation coefficients: 3.7 and 3.7 S; partial specific volumes: 0.75 and 0.78 ml · g −1 molecular weight: 83000 and 80000. These results indicate that the marked functional differences between liver and kidney receptors are not accompanied by appreciable differences in molecular size.