Abstract
1. The aim of this study was to provide a pharmacological characterization of the Y receptor types responsible for neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) effects upon electrogenic ion transport in isolated human colonic mucosa. 2. Preparations of descending colon were voltage-clamped at 0 mV in Ussing chambers and changes in short-circuit current (I(sc)) continuously recorded. Basolateral PYY, NPY, human PP (hPP), PYY(3 - 36), [Leu(31), Pro(34)]PYY (Pro(34)PYY) and [Leu(31), Pro(34)]-NPY (Pro(34)NPY) all reduced basal I(sc) in untreated colon. Of all the Y agonists tested PYY(3 - 36) responses were most sensitive to tetrodotoxin (TTX) pretreatment, indicating that Y(2)-receptors are located on intrinsic neurones as well as epithelia in this tissue. 3. The EC(50) values for Pro(34)PYY, PYY(3 - 36) and hPP were 9.7 nM (4.0 - 23.5), 11.4 nM (7.6 - 17.0) and 14.5 nM (10.2 - 20.5) and response curves exhibited similar efficacies. The novel Y(5) agonist [Ala(31), Aib(32)]-NPY had no effect at 100 nM. 4. Y(1) receptor antagonists, BIBP3226 and BIBO3304 both increased basal I(sc) levels per se and inhibited subsequent PYY and Pro(34)PYY but not hPP or PYY(3 - 36) responses. The Y(2) antagonist, BIIE0246 also raised basal I(sc) levels and attenuated subsequent PYY(3 - 36) but not Pro(34)PYY or hPP responses. 5. We conclude that Y(1) and Y(2) receptor-mediated inhibitory tone exists in human colon mucosa. PYY and NPY exert their effects via both Y(1) and Y(2) receptors, but the insensitivity of hPP responses to either Y(1) or Y(2) antagonism, or to TTX, indicates that Y(4) receptors are involved and that they are predominantly post-junctional in human colon.