Characterization and distribution of binding sites for a new neurotensin receptor antagonist ligand, [3H]SR 48692, in the guinea pig brain.
SR 48692, a selective nonpeptide antagonist of neurotensin (NT) receptors was developed recently. In the present work we studied the binding properties of the corresponding radioligand, [3H]SR 48692, in the adult guinea pig brain. The characterization of [3H]SR 48692 binding was carried out on brain membrane preparations and the distribution of [3H]SR 48692 binding sites was determined by receptor autoradiography and compared to that of [125I]NT binding sites. In brain homogenates, [3H]SR 48692 bound to a single population of sites with a Kd of 2.19 nM and a maximal binding capacity of 1.15 pmol/mg of protein. This maximal binding capacity value was 20 times higher than that observed for [125I]NT. NT agonists were able to interact competitively with the entire population of binding sites labeled by [3H]SR 48692, but their affinities were much lower than those observed for [125I]NT. By contrast, NT antagonists exhibited similar abilities to inhibit the binding of both radioligands. The addition of unlabeled NT in saturation assays revealed a competitive inhibition of [3H]SR 48692 binding, suggesting that agonist and antagonist ligand bind to overlapping domains of the NT receptor. The autoradiographic distribution of the low-affinity NT binding sites detected by [3H]SR 48692 (96% of the receptors) was very similar to the distribution of high-affinity receptors labeled with [125I]NT (4% of the receptors). In addition, the binding of [3H]SR 48692 was insensitive to guanyl nucleotides. Taken together, these findings suggest that the binding sites detected by [3H]SR 48692 in the guinea pig brain mainly represent the uncoupled form of the NT receptor.
Betancur
C
C
Institut National de la Santé et de la Recherche Médicale U. 339, Hôpital Saint-Antoine, Paris, France.
Canton
M
M
Gully
D
D
Vela
G
G
Pélaprat
D
D
Rostène
W
W
D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D006168:Guinea Pigs; D007457:Iodine Radioisotopes; D008297:Male; D011720:Pyrazoles / Q000378:metabolism* / Q000493:pharmacokinetics; D011804:Quinolines / Q000378:metabolism* / Q000493:pharmacokinetics; D011869:Radioligand Assay; D018028:Receptors, Neurotensin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014316:Tritium
D007457:Iodine Radioisotopes; D011720:Pyrazoles; D011804:Quinolines; D018028:Receptors, Neurotensin; D014316:Tritium; C079087:SR 48692