CHARACTERIZATION OF VASOACTIVE-INTESTINAL-PEPTIDE RECEPTORS IN RAT SEMINAL-VESICLE

Receptors for vasoactive intestinal peptide (VIP) in membranes from rat seminal vesicle were examined using I-125-labeled VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on temperature and membrane concentration. At 15-degrees-C, the stoichiometric data suggested the presence of two classes of VIP receptors with K(d) values of 0.54 and 44.4 nM and binding capacities of 73 and 1,065 fmol VIP/mg membrane protein, respectively. The interaction showed a high degree of specificity, as suggested by competition experiments with various peptides structurally related to VIP as follows: helodermin was 10 times, secretin 30 times, and rat growth hormone-releasing factor 300 times less potent than VIP, whereas glucagon did not recognize VIP receptors in concentrations of up to 10-mu-M. The binding of I-125-VIP to membranes was sensitive to the presence of GTP in the incubation medium in a dose-dependent manner. To characterize the molecular weight of these VIP receptors, I-125-VIP was covalently bound to membranes from rat seminal vesicle using dithiobis(succinimidyl propionate); sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the solubilized receptor revealed the presence of a specific component with a molecular mass of 47,000 Da as estimated in denaturing conditions. These findings, together with the known presence of VIP-containing nerves in the seminal vesicle, suggest a direct physiological role for this peptide in this accessory gland of the male genital tract.