Presence of pituitary adenylate cyclase-activating polypeptide receptors in Y-79 human retinoblastoma cells.

Cytochemical analysis demonstrated that a high percentage of human Y-79 retinoblastoma cells displayed a specific labeling by the biotinyl derivative 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 of PACAP, the one with 38 (PACAP 38) and the other with 27 (PACAP 27) amino acids, displaced the binding of 125I-PACAP 27 with IC50 values in the picomolar range and increased adenylyl cyclase activity by 100-fold with EC50 values of 27 and 180 pM, respectively. VIP, human peptide histidine-isoleucine, glucagon, and secretin were much less effective and potent in both receptor assays. The PACAP receptor antagonists PACAP 6-27 and PACAP 6-38 and an antiserum directed against the stimulatory G protein Gs inhibited the PACAP stimulation of adenylyl cyclase. In intact cells, both PACAPs and VIP failed to stimulate the phosphoinositide hydrolysis, whereas in cell membranes PACAP 38, but not the other peptides, produced a modest increase (40%) of inositol phosphate formation with an EC50 value of 22 nM. However, this effect was not antagonized by either PACAP 6-38 or PACAP 6-27. These data demonstrate the presence in human Y-79 retinoblastoma cells of specific PACAP receptors and provide further evidence that PACAP may act as a neurotransmitter/neuromodulator in mammalian retina.