PEPTIDE YY RECEPTOR IN SUBMUCOSAL AND MYENTERIC PLEXUS SYNAPTOSOMES OF CANINE SMALL-INTESTINE

PYY receptors were characterized and their loci determined in canine s mall intestine. The density of I-125-labeled peptide tyrosine tyrosine (PYY) binding was highest in myenteric (MY) and submucosal (SUB) plex us fractions enriched in synaptosomes. Two binding sites [high affinit y (H) and low affinity (L)] were found in the submucosal synaptosome-e nriched membrane: dissociation constant (K-d)(H) = 7.6 pM, maximal bin ding capacity (B-max)(H) = 28 fmol/mg; K-dL = 0.18 nM, B-maxL = 120 fm ol/mg protein. The binding of I-125-PYY reached a maximum within 30 mi n; dissociation was incomplete in the presence of unlabeled PW. The ra te of dissociation was enhanced after exposure of synaptosomes to guan osine 5'-O-(3-thiotriphosphate). Binding of I-125-PYY was completely i nhibited by neuropeptide Y (NPY)-(13-36) (in SUB and MY) and by [Leu(3 1),Pro(34)]NPY (in MY) but only partially by [Leu(31),Pro(34)]NPY in S UB, suggesting the presence of Y-2 receptor in SUB and the presence of Y-1 and Y-2 receptors in MY. Sodium dodecyl sulfate-polyacrylamide ge l electrophoresis analysis of the PYY receptor complex revealed a radi oactive band at 70 kDa. The PYY receptors in the canine small intestin al myenteric and submucosal plexus correspond in location to that of P YY in synaptosomes and are coupled with G proteins. Different subtypes are present in different loci.