Characterization of 5‐HT3 receptors of N1E‐115 neuroblastoma cells by use of the influx of the organic cation [14C]‐guanidinium

Abstract

The 5‐HT3 receptor‐mediated cation influx into N1E‐115 mouse neuroblastoma cells has been studied by the use of the organic cation [14C]‐guanidinium. 5‐Hydroxytryptamine (5‐HT, 30 μm) caused a time‐dependent influx of [14C]‐guanidinium which, in contrast to the influx elicited by veratridine (100 μm), was not inhibited by tetrodotoxin (TTX, 10 μm). The 5‐HT‐induced influx was potentiated by substance P and inhibited by ondansetron. 5‐HT and the selective 5‐HT3 receptor agonists, m‐chloro‐phenylbiguanide, phenylbiguanide and 2‐methyl‐5‐HT caused bell‐shaped concentration‐response curves; the rank order of potency was m‐chlorophenylbiguanide > 5‐HT > phenylbiguanide = 2‐methyl‐5‐HT. Among these agonists, 5‐HT elicited the highest influx of [14C]‐guanidinium. 5‐Methoxytryptamine, an agonist at 5‐HT4 receptors, showed no effect. The [14C]‐guanidinium influx induced by 100 μm 5‐HT was not affected by methysergide (10 μm) and ketanserin (10 μm) but was inhibited by 5‐HT3 receptor antagonists with the following rank order of potency: ICS 205–930 > ondansetron > MDL 72222 ≫ metoclopramide. The 5‐HT‐induced [14C]‐guanidinium influx was increased in the absence of Ca2+ and/or Na+ and by a reduction of the temperature from 36° to 20°C. Preincubation with 5‐HT (100 μm) caused a time‐dependent and rapidly reversible decrease of the 5‐HT‐induced [14C]‐guanidinium influx. It is concluded that [14C]‐guanidinium influx measurement in N1E‐115 cells is a convenient method to study properties of the cation channel of the 5‐HT3 receptor. This influx is independent of the fast sodium channel. 1993 British Pharmacological Society