M. Barann et al., INCREASING EFFECT OF ETHANOL ON 5-HT3 RECEPTOR-MEDIATED C-14 GUANIDINIUM INFLUX IN N1E-115 NEUROBLASTOMA-CELLS, Naunyn-Schmiedeberg's archives of pharmacology, 352(2), 1995, pp. 149-156
N1E-115 mouse neuroblastoma cells were used to study the influence of
ethanol on the 5-HT- and veratridine-induced influx of C-14-guanidiniu
m via the 5-HT3 receptor channel and the fast sodium channel, respecti
vely. Ethanol (10-100 mM) concentration-dependently increased the 5-HT
-induced C-14-guanidinium influx, leaving the basal and veratridine (1
00 mu M)-induced influx unaffected. The increasing effect of ethanol (
100 mM) was observed at all 5-HT concentrations investigated; accordin
gly, ethanol increased the maximum response to 5-HT. Whereas in the ab
sence of ethanol the concentration-response curve for 5-HT was bell-sh
aped, this was no longer the case when ethanol (100 mM) was present in
the incubation buffer; the descending branch of the concentration-res
ponse curve for 5-HT at concentrations above 300 mu M was virtually no
longer observed. When, in the presence of substance P (10 mu M) the 5
-HT-induced C-14-guanidinium influx was already enhanced, the ability
of ethanol (100 mM) to increase the 5-HT-induced influx was considerab
ly diminished (by 72%). Preincubation of N1E-115 cells with 5-HT cause
d a decay of the subsequent 5-HT response (''desensitization'') which
was dependent on the duration of preincubation; ethanol (100 mM) did n
ot affect the rate of this decay of the 5-HT response. The 5-HT (30 mu
M)-induced C-14-guanidinium influx was also increased by methanol (10
0 mM) and n-propanol (100 mM). The rank order of the increasing effect
of the n-alkanols (at 100 mM) was: methanol < ethanol < n-propanol; i
.e. the degree of enhancement increased with the lipophilicity of the
alcohols. Ethanol (100 mM) did not alter the time-course of non-specif
ic and specific binding of the selective 5-HT3 receptor antagonist H-3
-GR 65630 to intact N1E-115 cells. In competition binding experiments,
inhibition of H-3-GR 65630 binding by 5-HT was characterized by a hig
h affinity (pIC(50) = 4.71 +/- 0.19) and a low affinity component (pIC
(50) = 2.65 +/- 0.03). Ethanol did not affect the 5-HT-induced inhibit
ion of H-3-GR 65630 binding. These results indicate that ethanol does
not interfere with the 5-HT recognition site of the 5-HT3 receptor. Si
nce the enhancement of cation influx by alcohols increased in proporti
on to their lipophilicity, it is suggested that ethanol and other n-al
kanols interact with a hydrophobic region of the 5-HT3 receptor channe
l. In analogy to its effect on the nicotinic receptor channel, ethanol
may stabilize the open state of the 5-HT3 receptor channel.