INCREASING EFFECT OF ETHANOL ON 5-HT3 RECEPTOR-MEDIATED C-14 GUANIDINIUM INFLUX IN N1E-115 NEUROBLASTOMA-CELLS

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.