Characteristics of [14C]guanidinium accumulation in NG 108-15 cells exposed to serotonin 5-HT3 receptor ligands and substance P.
In the presence of substance P (SP; 10 microM), serotonin (5-HT; 1 microM) triggered a cation permeability in cells of the hybridoma (mouse neuroblastoma x rat glioma) clone NG 108-15 that could be assessed by measuring the cell capacity to accumulate [14C]guanidinium for 10-15 min at 37 degrees C. In addition to 5-HT (EC50 0.33 microM), the potent 5-HT3 receptor agonists 2-methyl-serotonin, phenylbiguanide, and m-chlorophenylbiguanide, and quipazine, markedly increased [14C]guanidinium uptake in NG 108-15 cells exposed to 10 microM SP. In contrast, 5-HT3 receptor antagonists prevented the effect of 5-HT. The correlation (r = 0.97) between the potencies of 16 different ligands to mimic or prevent the effects of 5-HT on [14C]guanidinium uptake, on the one hand, and to displace [3H]zacopride specifically bound to 5-HT3 receptors on NG 108-15 cells, on the other hand, clearly demonstrated that [14C]guanidinium uptake was directly controlled by 5-HT3 receptors. Various compounds such as inorganic cations (La3+, Mn2+, Ba2+, Ni2+, and Zn2+), D-tubocurarine, and memantine inhibited [14C]guanidinium uptake in NG 108-15 cells exposed to 5-HT and SP, as expected from their noncompetitive antagonistic properties at 5-HT3 receptors. However, ethanol (100 nM), which has been reported to potentiate the electrophysiological response to 5-HT3 receptor stimulation, prevented the effects of 5-HT plus SP on [14C]guanidinium uptake. The cooperative effect of SP on this 5-HT3-evoked response resulted neither from an interaction of the peptide with the 5-HT3 receptor binding site nor from a possible direct activation of G proteins in NG 108-15 cells. Among SP derivatives, [D-Pro9]SP, a compound inactive at the various neurokinin receptor classes, was the most potent to mimic the stimulatory effect of SP on [14C]guanidinium uptake in NG 108-15 cells exposed to 5-HT. Although the cellular mechanisms involved deserve further investigations, the 5-HT-evoked [14C]guanidinium uptake appears to be a rapid and reliable response for assessing the functional state of 5-HT3 receptors in NG 108-15 cells.
Emerit
M B
MB
INSERM U288, Neurobiologie Cellulaire et Fonctionnelle, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
Riad
M
M
Fattaccini
C M
CM
Hamon
M
M
D000818:Animals; D001549:Benzamides / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002250:Carbon Radioisotopes; D002412:Cations; D004305:Dose-Response Relationship, Drug; D005910:Glioma; D019791:Guanidine; D006146:Guanidines / Q000378:metabolism*; D006822:Hybrid Cells; D007700:Kinetics; D051379:Mice; D009447:Neuroblastoma; D009479:Neuropeptides / Q000494:pharmacology; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000378:metabolism / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013373:Substance P / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D001549:Benzamides; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002250:Carbon Radioisotopes; D002412:Cations; D006146:Guanidines; D009479:Neuropeptides; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D013373:Substance P; C055971:zacopride; D019791:Guanidine