Ligand association with the rabbit kidney and brain Y-1, Y-2 and Y-5-like neuropeptide Y (NPY) receptors shows large subtype-related differences in sensitivity to chaotropic and alkylating agents

The binding to rabbit kidney or hypothalamic particulates of the subtype-se lective neuropeptide Y (NPY) receptor ligands [I-125](Leu(31),Pro(34))hPYY (as Y-1 site label at 2 nM human pancreatic polypeptide (hPP)), [I-125]-hPY Y(3-36) (Y-2 label), and [I-125]-hPP (Y-5 label) displayed great difference s in sensitivity to alkylators and chaotropic agents. Sensitivity to a noni onic chaotrope, urea, was much higher for the Y-1 binding than for the Y-5- like binding or the Y-2 binding. The non-selective alkylator N-ethylmaleimi de (NEM) and several alkylators selective for aminergic receptors were much more efficacious against the Y-1 relative to the Y-2 binding. Similar diff erences could be confirmed with the attachment of Y-1 and Y-2-selective tra cers to CHO cells expressing the cloned guinea-pig Y-1 or Y-2 receptors, Th e Y-5-like binding was quite insensitive to NEM, but sensitive to chloroeth ylclonidine (CEC) and prazobind, which were less potent at the Y-1, and esp ecially at the Y-2 site. The unrestricted-access alkylator 2-aminoethyl met hanethiosulfonate inhibited the binding to all subtypes, while the restrict ed-access agent 2-(trimethylammonium)ethylmethanethiosulfonate poorly inhib ited the Y-5-like binding, or the guanine nucleotide-insensitive Y-2 bindin g. These results are compatible with an active conformation of the Y-5-like site dependent on maintenance of a shared hydrophobic cavity. The Y, sites resistant to guanosine polyphosphates and restricted-access alkylators wer e detected mainly in particulates slowly solubilized by cholate at 0-5 degr ees C; these sites could be clustered. (C) 2000 Elsevier Science B.V. All r ights reserved.