Antagonism of 5-HT₃ receptor mediated currents in murine N1E-115 neuroblastoma cells by (+)-tubocurarine

5-HT₃ receptor-mediated membrane currents were recorded from voltage-clamped clonal N1E-115 neuroblastoma cells. The inward current response to ionophoretically applied serotonin (5-HT) was reversibly antagonised by the 5-HT₃ receptor antagonists GR 38032F and metoclopramide with IC₅₀ values of 0.2 nM and 14 nM, respectively. Low concentrations of (+)-tubocurarine ((+)-Tc) also blocked the response to 5-HT (IC₅₀ = 0.8 nM), but other nicotinic cholinoceptor antagonists (gallamine, vecuronium and trimetaphan) were ineffective when applied at a relatively high concentration (1 μM). Blockade by (+)-Tc was neither voltage- nor use-dependent, suggesting that (+)-Tc does not block 5-HT-activated ion channels in N1E-115 cells.