Figure 5.

Ion substitution shows that responses to NaCl derive from the chloride ion. Taste buds were focally and sequentially stimulated with NaCl (black traces) and matched concentrations of one other salt (gray traces). Traces represent an example from each type of ion substitution. Plots represent response amplitudes to NaCl stimulation (filled circles) and to the other salt (open circles). Error bars indicate means and 95% CI. A, KCl (70–310 mm) elicited responses in all cells that responded to NaCl (70–350 mm). Amplitudes were significantly different between NaCl and KCl (t₍₈₎ = 3.6, p = 0.007, n = 9 cells, 2 mice) with a mean decrease of 46%. B, Choline chloride (ChCl, 170–340 mm) elicited responses in all cells that responded to NaCl (110–360 mm). Response amplitudes were not significantly different between matched concentrations of NaCl and ChCl (t₍₁₀₎ = 2.0, p = 0.069, n = 11 cells, 2 mice). C, Taste buds were stimulated with NaCl (90–340 mm) and NaBr (100–370 mm). All cells responded to both salts; responses to NaBr were smaller, a significant difference (t₍₇₎ = 6.1, p = 0.0005, n = 8 cells, 2 mice). D, Sodium gluconate (NaGluc, 150–370 mm) did not elicit responses in any of the NaCl (120–370 mm)-responsive cells (t₍₅₎ > 7, p < 0.0001, n = 6 cells, 2 mice). In all plots, the data for NaCl represent the mean of 2 or 3 replicate responses from each cell. In this series of experiments, the salt concentrations are noted as the concentration above that already present in Tyrode's buffer. E, Lingual slices were maintained in Na⁺-free NMDG-Tyrode's buffer (shaded) and stimulated with NaCl (90–290 mm; left), followed by matched concentrations of choline Cl (ChCl, middle). Responses are refractory to the complete elimination of permeable Na⁺_, and response amplitudes to NaCl or choline chloride showed no significant difference (t₍₇₎ = 0.17, p = 0.87, n = 8 cells, 2 mice). n.s. = not significant. Calibration: A–E, 20 s, 0.5 ΔF/F.