title: Identification of key residues that cause differential gallbladder response to PACAP and VIP in the guinea pig.
abstract: Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have opposite actions on the gallbladder; PACAP induces contraction, whereas VIP induces relaxation. Here, we have attempted to identify key residues responsible for their interactions with PACAP (PAC1) and VIP (VPAC) receptors in the guinea pig gallbladder. We synthesized PACAP-27/VIP hybrid peptides and compared their actions on isolated guinea pig gallbladder smooth muscle strips using isotonic transducers. [Ala4]- and [Val5]PACAP-27 were more potent than PACAP-27 in stimulating the gallbladder. In contrast, [Ala4, Val5]- and [Ala4, Val5, Asn9]PACAP-27 induced relaxation similarly to VIP. [Asn9]-, [Thr11]-, or [Leu13]PACAP-27 had 20-70% contractile activity of PACAP-27, whereas [Asn24,Ser25,Ile26]PACAP-27 showed no change in the activity. All VIP analogs, including [Gly4,Ile5,Ser9]VIP, induced relaxation. In the presence of a PAC1 receptor antagonist, PACAP(6-38), the contractile response to PACAP-27 was inhibited and relaxation became evident. RT-PCR analysis revealed abundant expressions of PAC1 receptor, "hop" splice variant, and VPAC1 and VPAC2 receptor mRNAs in the guinea pig gallbladder. In conclusion, PACAP-27 induces contraction of the gallbladder via PAC1/hop receptors. Gly4 and Ile5 are the key NH2-terminal residues of PACAP-27 that distinguish PAC1/hop receptors from VPAC1/VPAC2 receptors. However, both the NH2-terminal and alpha-helical regions of PACAP-27 are required for initiating gallbladder contraction.
authors.affiliation: The First Affiliated Hospital of Nanjing Medical University, Nanjing, China.
authors.forename: Muxin
authors.initials: M
authors.lastname: Wei
authors.forename: Kotoyo
authors.initials: K
authors.lastname: Fujiki
authors.forename: Eiji
authors.initials: E
authors.lastname: Ando
authors.forename: Sumin
authors.initials: S
authors.lastname: Zhang
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Ozaki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishiguro
authors.forename: Takaharu
authors.initials: T
authors.lastname: Kondo
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Nokihara
authors.forename: Victor
authors.initials: V
authors.lastname: Wray
authors.forename: Satoru
authors.initials: S
authors.lastname: Naruse
mesh_terms: D000818:Animals; D005704:Gallbladder / Q000187:drug effects / Q000502:physiology*; D006168:Guinea Pigs; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
chemical_list: D010446:Peptide Fragments; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D014660:Vasoactive Intestinal Peptide