Three receptors for VIP and pituitary adenylate cyclase-activating peptide (PACAP) have been cloned and characterized: PAC1, with high affinity for PACAP, and VPAC1 and VPAC2 with equally high affinity for VIP and PACAP. The existence of a VIP-specific receptor (VIPs) in guinea pig (GP) teniae coli smooth muscle was previously surmised on the basis of functional studies, and its existence was confirmed by cloning of a partial NH2-terminal sequence. Here we report the cloning of the full-length cDNAs of two receptors, a VPAC2 receptor from GP gastric smooth muscle and VIPs from GP teniae coli smooth muscle. The cDNA sequence of the VIPs encodes a 437-amino acid protein ( Mr 49,560) that possesses 87% similarity to VPAC2 receptors in rat and mouse and differs from the VPAC2 receptor in GP gastric smooth muscle by only two amino-acid residues, F40F41 in lieu of L40L41. In COS-1 cells transfected with the GP teniae coli smooth muscle receptor, only VIP bound with high affinity (IC50 1.4 nM) and stimulated cAMP formation with high potency (EC50 1 nM). In contrast, in COS-1 cells transfected with the GP gastric smooth muscle receptor, both VIP and PACAP bound with equally high affinity (IC50 2.3 nM) and stimulated cAMP with equally high potency (EC50 1.5 nM). We conclude that the receptor cloned from GP teniae coli smooth muscle is a VIPs distinct from VPAC1 and VPAC2 receptors. The ligand specificity in this species is determined by a pair of adjacent phenylalanine residues (L40L41) in the NH2-terminal ligand-binding domain.
M2 and M3 Muscarinic Receptors Couple, Respectively, With Activation of Nonselective Cationic Channels and Potassium Channels in Intestinal Smooth Muscle Cells
