Investigation and characterization of receptors for pituitary adenylate cyclase-activating polypeptide in human brain by radioligand binding and chemical cross-linking.
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a novel peptide of hypothalamic origin which increases adenylate cyclase activity in rat anterior pituitary cell cultures. The 38-amino acid peptide shows a close sequence homology to vasoactive intestinal peptide (VIP). Binding sites for PACAP in membranes from postmortem human brain tissue were studied using [125I]PACAP27 as the radioligand. High specific binding sites (amount of specific binding measured at 0.25 nM [125I]PACAP27 in femtomoles per mg protein +/- SEM; n = 4) were present in hypothalamus (344.5 +/- 13.0), brain stem (343.0 +/- 29.3), cerebellum (292.0 +/- 21.1), cortex (259.6 +/- 19.8), and basal ganglia (259.2 +/- 50.3). Specific binding sites in pituitary, although present, were less abundant (35.0 +/- 8.9). Binding of [125I]PACAP27 was reversible and time, pH, and temperature dependent. Despite the homology with VIP, VIP was a poor inhibitor of [125I]PACAP27 binding (IC50, greater than 1 microM) compared with PACAP27 (IC50, 0.5-1.3 nM) and PACAP38 (IC50, 0.2-1.3 nM). Scatchard plots of [125I]PACAP27 binding showed the presence of both high and lower affinity sites. Chemical cross-linking of PACAP-binding sites revealed that [125I]PACAP27 was bound to polypeptide chains of 67,000 and 48,000 mol wt. Thus, we have demonstrated the presence of PACAP-specific receptors in human brain which are not VIP receptors. This opens the possibility of PACAP functioning as a novel neurotransmitter/neuromodulator in human brain.
Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
K
K
Suda
D M
DM
Smith
M A
MA
Ghatei
J K
JK
Murphy
S R
SR
Bloom
D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D001923:Brain Chemistry; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D003432:Cross-Linking Reagents; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007457:Iodine Radioisotopes; D009479:Neuropeptides / Q000032:analysis* / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000502:physiology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000378:metabolism; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D011979:Receptors, Pituitary Hormone; D013696:Temperature; D013997:Time Factors
C495401:ADCYAP1 protein, human; D003432:Cross-Linking Reagents; D007457:Iodine Radioisotopes; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011956:Receptors, Cell Surface; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D011979:Receptors, Pituitary Hormone