Y4 receptors mediate the inhibitory responses of pancreatic polypeptide in human and mouse colon mucosa

The antisecretory effects of several Y agonists, including pancreatic polypeptide (PP), indicate the presence of Y-1, Y-2, and Y-4 receptors in mouse and human (h) colon mucosae. Here, we used preparations from human and from wild-type (WT), Y-4, and Y-1 receptor knockout ((-/-)) mice, alongside Y-4 receptor-transfected cells to define the relative functional contribution of the Y-4 receptor. First, rat (r) PP antisecretory responses were lost in murine Y-4(-/-) preparations, but hPP and Pro(34) peptide YY (PYY) costimulated Y-4 and Y-1 receptors in WT mucosa. The Y-1 antagonist/Y-4 agonist GR231118 [(Ile, Glu, Pro, Dpr, Tyr, Arg, Leu, Arg, Try- NH2)-2-cyclic(2,4 '),(2 ', 4)-diamide] elicited small Y-4-mediated antisecretory responses in human tissues pretreated with the Y-1 antagonist, BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]N-2-(diphenylacetyl)-argininamide trifluoroacetate)], and attenuated Y-4-mediated hPP responses in mouse and human mucosa. GR231118 and rPP were also antisecretory in hY(4)-transfected epithelial monolayers but were partial agonists compared with hPP at this receptor. In Y-4-transfected human embryonic kidney (HEK) 293 cells, Y-4 ligands displaced [I-125]hPP binding with orders of affinity (pK(i)) at human (hPP = rPP > GR231118 > Pro(34)PYY = PYY) and mouse (rPP = hPP > GR231118 > Pro(34)PYY > PYY) Y-4 receptors. GR231118- and rPP-stimulated guanosine 5 '-3-O-(thio)triphosphate binding through hY(4) receptors with significantly lower efficacy than hPP. GR231118 marginally increased basal but abolished further PP-induced hY(4) internalization to recycling (transferrin-labeled) pathways in HEK293 cells. Taken together, these findings show that Y-4 receptors play a definitive role in attenuating colonic anion transport and may be useful targets for novel antidiarrheal agents due to their limited peripheral expression.