Selective activation of G protein subtypes in the vomeronasal organ upon stimulation with urine-derived compounds

Chemosensory neurons in the vomeronasal organ (VNO) detect pheromones related to social and reproductive behavior in most terrestrial vertebrates. Current evidence indicate that the chemoelectrical transduction process is mediated by G protein-coupled second messenger cascades. In the present study, attempts were made to identify the G protein subtypes which are activated upon stimulation with urinary pheromonal components. G protein-specific antibodies were employed to interfere specifically with inositol 1,3,4-trisphosphate formation induced by urinary stimuli and to immunoprecipitate G alpha-subunits, activation dependently labeled with [alpha-P-32]GTP azidoanilide. The results of both experimental approaches indicate that stimulation of female VNO membrane preparations with male urine samples induces activation of G(i) as well as G(o) subtypes, Experiments using different fractions of urine revealed that upon stimulation with lipophilic volatile odorants, only G(i) proteins were activated, whereas G(o) activation was elicited by alpha(2u)-globulin, a major urinary protein, which is a member of the lipocalin superfamily, Since each G protein subtype is stereotypically coexpressed with one of the two structurally different candidate pheromone receptors (V1R and V2R), the results provide the first experimental evidence that V1Rs coexpressed with G(i) may be activated by lipophilic probably volatile odorants, whereas V2Rs coexpressed with G(o) seem to be specialized to interact with pheromonal components of proteinaceous nature.