VIP receptors on canine submucosal synaptosomes

The present study characterized ¹²⁵I]VIP binding to synaptosomes from the submucosa of canine small intestine. Studies of saturation, competition binding, and kinetic studies revealed high- and low-affinity binding sites. Studies with GTP-γ-S and cholera toxin suggested that the receptor was coupled to a G-protein, possibly G_s. Competition with VIP analogs suggested that the N-terminal end of the molecule played the major role in determining affinity and that this receptor was for VIP, not PACAP. Cross-linking VIP to the receptor revealed a single peptide (M_r 60,000). We suggest that VIP may act to modulate mediator release from enteric nerve endings.