MELANOPHORE PIGMENT DISPERSION RESPONSES TO AGONISTS SHOW 2 PATTERNS OF SENSITIVITY TO INHIBITORS OF CAMP-DEPENDENT PROTEIN-KINASE AND PROTEIN-KINASE-C

Melanophore pigment dispersion is a sensitive bioassay for activation of the adenylyl cyclase and phospholipase C second-messenger pathways. The necessity of protein kinase activation in causing pigment dispers ion was confirmed for eight agonists of endogenous melanophore recepto rs and for two transfected receptors. All agonists and receptors previ ously shown to elevate intracellular cAMP in melanophores-melanocyte s timulating hormone, light, (-) norepinephrine, 5-hydroxytrptamine, and the beta(2)-adrenergic receptor-were able to stimulate pigment disper sion in the presence of Ro31-8220, a potent inhibitor of protein kinas e C, but were blocked in the presence of H89, an inhibitor of cAMP-dep endent protein kinase. The bombesin receptor, which elevates intracell ular IP3 in melanophores, was unable to stimulate pigment dispersion i n the presence of Ro31-8220 or H89. Agonists whose mechanism of activa tion of pigment dispersion are unknown were also tested. Endothelin 3 responses were blocked by both H89 and Ro31-8220, predicting coupling to phospholipase C. Vasoactive intestinal polypeptide, oxytocin, and c alcitonin gene-related peptide beta responses were blocked only by H89 , predicting coupling to adenylyl cyclase. (C) 1996 Wiley-Liss, Inc.