Functional characterization of a receptor for vasoactive-intestinal-peptide-related peptides in cultured dermal melanophores from Xenopus laevis

A receptor for vasoactive-intestinal-peptide (VIP)-related peptides was fun ctionally characterized in a cell line derived from Xenopus melanophores us ing a recently described microtiter-plate-based bioassay, Activation of the melanophore VIP receptor by VIP or the peptides pituitary-adenylate-cyclas e-activating polypeptide (PACAP 38), PACAP 27, and helodermin stimulated in tracellular 3'-5' cyclic adenosine monophosphate (cAMP) accumulation and pi gment dispersion in the cells, Helodermin, with an EC50 (concentration of p eptide inducing half-maximal melanosome dispersion) of 46.5 pM, was the mos t potent activator of pigment dispersion, followed by PACAP 38 > VIP > PACA P 27, A similar order of potencies was observed for the peptides to induce cAMP accumulation, The responses to VIP agonists were selectively inhibited by the VIP antagonists PACAP-(6 - 27) and (N-Ac-Tyr(1)-D-Phe(2))-growth-ho rmone-releasing factor[GRF](1-29)-NH2. Taken together, the results suggest that the melanophores express a VIP receptor that shares certain characteri stics of, but also differs significantly from, other previously identified VIP receptors.