Common pharmacological and physico-chemical properties of 5-HT3 binding sites in the rat cerebral cortex and NG 108-15 clonal cells.
On account of the postulated existence of 5-HT3 receptor subtypes, the respective physico-chemical and pharmacological properties of specific binding sites for the potent 5-HT3 antagonist [3H]zacopride were compared using membranes from the rat posterior cortex or neuroblastoma-glioma NG 108-15 clonal cells. In both membrane preparations, [3H]zacopride bound to a single class of specific sites with a Kd close to 0.5 nM. However, the Bmax value in NG 108-15 cell membranes (970 +/- 194 fmol/mg protein) was approximately 50 times larger than that in cortical membranes (19 +/- 2 fmol/mg protein). The specific binding of [3H]zacopride was equally affected by temperature, pH and molarity of the assay medium, and equally insensitive to thiol- and disulfide-reagents (N-ethylmaleimide, p-chloromercuribenzene sulfonic acid, dithiothreitol) and GTP in cortical as well as NG 108-15 cell membranes. Determination of the molecular size of [3H]zacopride specific binding sites by radiation inactivation yielded values close to 35 kDa for both membrane preparations. Finally, a highly significant positive correlation (r = 0.979) was found between the respective pKi values of 34 different drugs for their inhibition of [3H]zacopride specific binding to cortical or NG 108-15 cell membranes. Among them, the most potent was S(-)zacopride (pKi = 9.55), followed by BRL 43964, ICS 205-930, quipazine, R(+)zacopride, GR 38032F and MDL 72222. Atypical antidepressants (mianserin, amoxapine) and neuroleptics (clotiapine, loxapine and clozapine) were active in rather low concentrations (pKi less than 6.5), suggesting that recognition of 5-HT3 sites might be relevant to part of the in vivo effects of these drugs. Such identical physico-chemical and pharmacological properties of [3H]zacopride specific binding in cortical and NG 108-15 cell membranes strongly suggest that the same 5-HT3 receptor (subtype?) exists in these two preparations.
Bolaños
F J
FJ
I.N.S.E.R.M. U288, Neurobiologie Cellulaire et Fonctionnelle, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
Schechter
L E
LE
Miquel
M C
MC
Emerit
M B
MB
Rumigny
J F
JF
Hamon
M
M
Gozlan
H
H
D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects / Q000528:radiation effects; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002412:Cations; D002462:Cell Membrane / Q000187:drug effects; D002540:Cerebral Cortex / Q000187:drug effects*; D002999:Clone Cells / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000737:chemistry / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013696:Temperature
D001549:Benzamides; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002412:Cations; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; C055971:zacopride