Vol. 286, Issue 1, 382-391, July 1998

Characterization of G Protein and Phospholipase C-Coupled Agonist Binding to the Y₁ Neuropeptide Y Receptor in Rat Brain: Sensitivity to G Protein Activators and Inhibitors and to Inhibitors of Phospholipase C

Steven L. Parker, Michael S. Parker, Trevor Sweatman and William R. Crowley

Department of Pharmacology, University of Tennessee School of Medicine, Memphis, Tennessee 38163 (S.L.P., T.S., W.R.C.), and Department of Microbiology, University of Memphis, Memphis, Tennessee 38152 (M.S.P.)

Binding of a Y₁-subtype-selective agonist of neuropeptide Y (NPY) receptor, (Leu³¹,Pro³⁴)human peptide YY (LP-PYY), to particulates from four rat brain areas (parietal cortex area 1, piriform cortex, anterior hypothalamus and hippocampus) showed a distinct response to LP-PYY and PYY, a uniformly low sensitivity to ligands selective for the Y₂, Y₄ and Y₅ NPY receptor subtypes and high sensitivity to a Y₁ site-selective antagonist, BIBP-3226. The Y₁ binding was sensitive to guanine nucleotide-binding protein (G protein) agonist and antagonist nucleotides, with the rank order of guanosine 5'-O-(thiotriphosphate) (GTPS) > GTP > GDP > guanosine 5'-O-(thiodiphosphate). However, guanine nucleotides did not affect about one third of the specific Y₁ binding. Most of Y₁ binding could be inhibited by a G protein nucleotide site/docking site receptor mimic, mastoparan analog MAS-7. In all areas examined, the Y₁ binding of LP-PYY was little affected by up to 100 µM of the antagonists of K⁺, Na⁺ and Ca⁺⁺ channels, protein kinase C, phospholipase A₂, phospholipase D and phosphatidylinositol 3-kinase, phospholipase substrate phospholipids, steroids or detergents. However, the binding was potently inhibited by phospholipase C inhibitors (especially the aminosteroid U-73122), which also dissociated the bound Y₁ ligand in steady-state conditions. U-73122 also displaced the Y₁ binding insensitive to GTPS. Ligand association with the brain Y₁ NPY receptor thus strongly depends on activity of both G proteins and phospholipase C, implying specific interactions of these transducers/effectors with the receptor molecule in ligand binding. A portion of brain Y₁ sites could be directly coupled to phospholipase(s) C.