Effects of 5-HT and its analogs on proton-evoked ASIC3 currents. A, Representative current traces showing the effects of various concentrations of 5-HT on pH 5.0-induced currents in CHO cells expressing ASIC3. Dashed lines indicate the sustained current induced by pH 5.0 alone. B, Means ± SEM peak (open symbols) and sustained (filled symbols) currents normalized to that induced by pH 5.0 alone. n = 5–8. Solid line for sustained currents represents a fit to the Hill equation. C, Chemical structures of 5-HT and its precursors and metabolites. D, Sustained ASIC3 currents induced by pH 5.0 in the presence of 5-HT (50 μm) and its analogs, l-tryptophan (TRP; 50 μm), 5-hydroxy-l-tryptophan (5-HTP; 50 μm), or 5-hydroxyindoleacetic acid (5-HIAA; 50 μm). Data are means ± SEM sustained currents normalized to that induced by pH 5.0 alone (dashed line indicates control). n = 4–6. **p < 0.01 versus control.