In N1E-115 mouse neuroblastoma cells, we studied the influence of sodium ion substitutes on the 5-HT-induced flux of 14C-guanidinium through the cation channel of the 5-HT3-R and on the competition of 5-HT with binding of the selective 5-HT3-R antagonist 3H-GR 65630 (Barann et al. 2004). The gene discussed is HTR3A; the disease is neuroblastoma.