Identification of chemoattractant receptors and G-proteins in the vomeronasal system of garter snakes.

Garter snakes respond to purified chemoattractants derived from prey. The specific binding sites for one of these chemoattractants, ES20, in the vomeronasal organ was saturable and reversible. Binding sites for ES20 were abolished by heating or greatly reduced by Pronase digestion. ES20 chemoattractant activity and receptor binding required Ca2+. Binding of ES20 to sensory epithelium derived from animals with bipolar neurons depleted by denervation was reduced 22-43% as compared to control animals. However, there was an upregulation of the ES20 receptor population in the nonsensory cells following nerve cuts. Three G-proteins (Gs, Gi, and G(o)) were tentatively identified using immunoreactivity and ADP-ribosylation techniques. Gi and G(o) proteins were shown to be coupled with ES20-receptor and effectors as evidenced by: 1) the affinity of ES20-receptor was decreased by GTP gamma S; 2) ES20-receptor binding caused a reduction in ADP-ribosylation of pertussis toxin-susceptible G-proteins, and the inhibitory effect of ES20-receptor on ADP-ribosylation was attenuated by GDP beta S; 3) the effect of ES20-receptor on ADP-ribosylation of the pertussis toxin-susceptible G-proteins could be mimicked by G-protein activators, such as GTP gamma S or AlF3; 4) ES20-receptor binding resulted in a decrease of the basal level of cAMP; 5) the binding of ES20 to its receptors caused an increase in the level of D-myo-inositol 1,4,5-trisphosphate.