Ehf. Wong et al., DIFFERENT DENSITIES OF 5-HT(3) RECEPTORS ARE LABELED BY [H-3] QUIPAZINE, [H-3] GR-65630 AND [H-3] GRANISETRON, Neuropharmacology, 32(9), 1993, pp. 869-875
The binding of three, structurally distinct 5-hydroxytryptamine3 (5-HT
3) receptor radioligands was characterized in rat cerebral cortex, rab
bit ileum myenteric plexus and NG- 108- 1 5 neuroblastoma cells. The d
ensity of sites labeled by the three ligands in rat cortex or in rabbi
t ileum was markedly different. [H-3]Quipazine labeled more sites than
[H-3]GR 65630 in rat cortex (4.0-fold) and rabbit ileum (1.9-fold), b
ut not in NG-108-15 cells. [H-3]Quipazine also labeled a greater densi
ty of sites than [H-3]granisetron in rat cortex (7-fold) but not in NG
-108 cells. [H-3]Quipazine binding in rat cortex and rabbit ileum, but
not in NG-108-15 cells, was displaced by non-radiolabeled GR 65630 in
a consistent with an interaction with more than one site. These data
indicate that not all 5-HT3 receptor radioligands recognize the same p
opulation of 5-HT3 binding sites with equivalent density and further s
uggest the existence of subtypes of 5-HT3 receptor binding sites in mt
cortical and rabbit myenteric plexus preparations.