[3H]BIMU-1, a 5-hydroxytryptamine3 receptor ligand in NG-108 cells, selectively labels sigma-2 binding sites in guinea pig hippocampus.
The binding of [3H]endo-N-(8-methyl-8-azabicyclo[3.2.1.]oct-3-yl)- 2,3-dihydro-3-ethyl-2-oxo-1H-benzimidazole-1-carboxamide hydrochloride ([3H]BIMU-1) a benzimidazolone with high affinity for 5-hydroxytryptamine (5-HT)3 and 4 5-HT3 and 5-HT4 receptors, was characterized in NG-108 cells and guinea pig hippocampus. Specific, heat-sensitive, binding of [3H]BIMU-1 was detected in both NG-108 cells and guinea pig hippocampus. In NG-108 cell membranes, a portion of the specific binding was displaced by 5-HT3 receptor ligands with affinities and specificity consistent with the labeling of 5-HT3 receptors. The residual specific binding was insensitive to serotonin (Ki > 1 mM) but was displaced by haloperidol (Ki of 50 nM). In guinea pig hippocampal membranes [3H]BIMU-1 binding was insensitive to serotonin but was displaced by haloperidol, and 1,3-di-o-tolyl-guanidine with affinities appropriate for the labeling of a sigma binding site (Ki of 6.3 and 31 nM, respectively). The affinity profile of ligands displacing [3H] BIMU-1 binding in guinea pig hippocampus was consistent with the selective labeling of a sigma-2 binding site because the sigma-1 selective benzomorphans, (+)-pentazocine and (+)-N-allylnormetazocine, only weakly displaced the binding (Ki greater than 1 microM). The affinity of BIMU-1 for sigma-2 binding sites (Ki = 32 nM) was 200-fold greater than that for sigma-1 binding sites (Ki = 6.3 microM), dopamine (D1 and D2), other serotonin (5-HT1A, 5-HT2A, 5-HT2C) and muscarinic (M1, M2, M3 and M4) receptors (Ki > 10 microM). The distribution of haloperidol-sensitive [3H]BIMU-1 binding was also consistent with the labeling of sigma-2 binding sites. These data suggest that [3H]BIMU-1 selectively labels sigma-2 binding sites in guinea pig hippocampus. [3H]BIMU-1, under appropriate experimental conditions, is thus the first sigma-2 binding site radioligand to be characterized.
Bonhaus
D W
DW
Department of Neurosciences, Syntex Discovery Research, Palo Alto, California.
Loury
D N
DN
Jakeman
L B
LB
To
Z
Z
DeSouza
A
A
Eglen
R M
RM
Wong
E H
EH
D000818:Animals; D001345:Autoradiography; D001562:Benzimidazoles / Q000378:metabolism*; D001665:Binding Sites; D001643:Bridged Bicyclo Compounds / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D006168:Guinea Pigs; D006624:Hippocampus / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008566:Membranes / Q000378:metabolism; D051379:Mice; D009447:Neuroblastoma; D010880:Piperidines / Q000378:metabolism; D051381:Rats; D011985:Receptors, Serotonin / Q000378:metabolism*; D017480:Receptors, sigma / Q000378:metabolism*; D012680:Sensitivity and Specificity; D014316:Tritium; D014407:Tumor Cells, Cultured
D001562:Benzimidazoles; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D010880:Piperidines; D011985:Receptors, Serotonin; D017480:Receptors, sigma; D014316:Tritium; C070187:(endo-N-8-methyl-8-azabicyclo(3.2.1)oct-3-yl)-2,3-dihydro-3-ethyl-2-oxo-1H-benzimidazol-1-carboxamide; C026539:preclamol