Mb. Emerit et al., CHARACTERISTICS OF [C-14] GUANIDINIUM ACCUMULATION IN NG 108-15 CELLSEXPOSED TO SEROTONIN 5-HT3 RECEPTOR LIGANDS AND SUBSTANCE-P, Journal of neurochemistry, 60(6), 1993, pp. 2059-2067
In the presence of substance P (SP: 10 muM), serotonin (5-HT; 1 muM) t
riggered a cation permeability in cells of the hybridoma (mouse neurob
lastoma x rat glioma) clone NG 108-15 that could be assessed by measur
ing the cell capacity to accumulate [C-14]guanidinium for 10-15 min at
37-degrees-C. In addition to 5-HT (EC50 0.33 muM), the potent 5-HT3 r
eceptor agonists 2-methyl-serotonin, phenylbiguanide, and m-chlorophen
ylbiguanide, and quipazine, markedly increased [C-14]guanidinium uptak
e in NG 108-15 cells exposed to 10 muM 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 [C-14]guanidinium uptake, on the one hand, and to d
isplace [H-3]zacopride specifically bound to 5-HT3 receptors on NG 108
-15 cells, on the other hand, clearly demonstrated that [C-14]guanidin
ium uptake was directly controlled by 5-HT3 receptors. Various compoun
ds such as inorganic cations (La3+, Mn2+, Ba2+, Ni2+, and Zn2+), D-tub
ocurarine, and memantine inhibited [C-14]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 mM)
, which has been reported to potentiate the electrophysiological respo
nse to 5-HT3 receptor stimulation, prevented the effects of 5-HT plus
SP on [C-14]guanidinium uptake. The cooperative effect of SP on this 5
-HT3-evoked response resulted neither from an interaction of the pepti
de with the 5-HT3 receptor binding site nor from a possible direct act
ivation of G proteins in NG 108-15 cells. Among SP derivatiVeS, [D-Pro
9]SP, a compound inactive at the various neurokinin receptor classes,
was the most potent to mimic the stimulatory effect of SP on [C-14]gua
nidinium uptake in NG 108-15 cells exposed to 5-HT. Although the cellu
lar mechanisms involved deserve further investigations, the 5-HT-evoke
d [C-14]guanidinium uptake appears to be a rapid and reliable response
for assessing the functional state of 5-HT3 receptors in NG 108-15 ce
lls.