PRESENCE OF PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE RECEPTORS IN Y-79 HUMAN RETINOBLASTOMA CELLS

Cytochemical analysis demonstrated that a high percentage of human Y-7 9 retinoblastoma cells displayed a specific labeling by the biotinyl d erivative of pituitary adenylate cyclase-activating polypeptide (PACAP ), a novel neuropeptide of the secretin-vasoactive intestinal peptide (VIP) family of peptides. In cell membranes, the two molecular forms o f PACAP, the one with 38 (PACAP 38) and the other with 27 (PACAP 27) a mino acids, displaced the binding of I-125-PACAP 27 with IC50 values i n the picomolar range and increased adenylyl cyclase activity by 100-f old with EC(50) values of 27 and 180 pM, respectively. VIP, human pept ide histidine-isoleucine, glucagon, and secretin were much less effect ive and potent in both receptor assays. The PACAP receptor antagonists PACAP 6-27 and PACAP 6-38 and an antiserum directed against the stimu latory G protein G(s) inhibited the PACAP stimulation of adenylyl cycl ase. In intact cells, both PACAPs and VIP failed to stimulate the phos phoinositide hydrolysis, whereas in cell membranes PACAP 38, but not t he other peptides, produced a modest increase (40%) of inositol phosph ate formation with an EC(50) value of 22 nM. However, this effect was not antagonized by either PACAP 6-38 or PACAP 6-27. These data demonst rate the presence in human Y-79 retinoblastoma cells of specific PACAP receptors and provide further evidence that PACAP may act as a neurot ransmitter/neuromodulater in mammalian retina.