Salt taste responses of the IXth nerve in Sprague-Dawley rats: Lack of sensitivity to amiloride

To explore characteristics of the salt taste function of taste receptor cells located on the posterior tongue, we recorded electrophysiological responses from the whole glossopharyngeal nerve in Sprague-Dawley (SD) rats. For all salts, relative response magnitudes increased with increased stimulus concentrations (0.2-2.0 M) of NH₄⁺, K⁺, and Na⁺ salts. The order of effectiveness of stimulation for Cl^- salts was NH₄Cl > KCl > NaCl. For sodium salts, relative response magnitudes were anion dependent. Sodium salts with small anions (NaCl, NaSCN, and NaNO₃) had a much stronger stimulating effect than sodium salts with large anion groups (Na₂SO₄, C₂H₃O₂Na, and C₆H₁₁O₇Na). The responses of the glossopharyngeal nerve to the Na⁺ salts of NaCl, C₂H₃O₂Na, and C₆H₁₁O₇Na were not inhibited by the lingual application of the epithelial sodium transport blocker amiloride. This is in contrast to large amiloride sensitivity of the chorda tympani nerve. Amiloride also failed to inhibit the responses to K⁺ salts (KCl and KC₂H₃O₂) and to NH₄Cl. These results demonstrate that taste receptors innervated by the glossopharyngeal nerve in SD rats lack amiloride sensitivity as observed in the glossopharyngeal nerve of spontaneously hypertensive and Wistar-Kyoto rats. Furthermore, the difference between the small-anion group and the large-anion group of Na⁺ salts in their effectiveness to produce responses in the glossopharyngeal nerve parallels the effects noted for the anion dependence in the portion of the taste response resistant to amiloride in the chorda tympani nerve. Sodium salts with the smaller anion produced the larger responses in both glossopharyngeal and chorda tympani nerves after amiloride.