Characterization of two novel tritiated radioligands for labelling Neuropeptide FF (NPFF(1) and NPFF(2)) receptors.

The binding characteristics of [(3)H]-NPVF and [(3)H]-EYF, the two first tritiated probes for the respective labelling of NPFF(1) and NPFF(2) receptors, are presented. In membranes from CHO cells transfected with the human NPFF(1) receptor, [(3)H]-NPVF labelled one class of binding sites with a high affinity (Bmax=4pmol/mg protein, Kd=2.65nM). In membranes from CHO cells transfected with the human NPFF(2) receptor, [(3)H]-EYF labelled one class of binding sites with a high affinity (Bmax=16pmol/mg protein, Kd=0.54nM). Both radioligands exhibited time-dependent binding, low (10-20%) non-specific binding and poor cross-reactivity towards the related receptor subtype. The potency of different NPFF ligands to displace [(3)H]-NPVF and [(3)H]-EYF binding profiles was in good agreement with the profile previously measured by using (125)I-probes (NPFF(1) receptor: NPVF> or =1DMe=SPA-NPFF>NPFF=SQA-NPFF=QFW-NPSF>NPSF>RF9; NPFF(2) receptor: SPA-NPFF>>SQA-NPFF=QFW-NPSF=1DMe=NPFF>>NPSF=NPVF>RF9). Therefore, [(3)H]-NPVF and [(3)H]-EYF are new valuable tools for performing binding on NPFF receptors.