Proton currents through amiloride-sensitive Na⁺ channels in isolated hamster taste cells: Enhancement by vasopressin and CAMP

Amiloride has been suggested to inhibit responses to a variety of taste stimuli, including salty, sweet, and sour (acid). To test for the involvement of amiloride-sensitive Na⁺ channels in the transduction of acid stimuli, fungi-form taste receptor cells were examined using patch-clamp techniques. Approximately one-half of all cells had amiloride-sensitive Na⁺ currents (I_Na) with a K_i value near 0.2 μM amiloride. After blocking voltage-gated conductances, cells having amiloride sensitivity were tested for responses to acid stimuli. Over three-fourths of cells showed an inward proton current (I_H+) with an extrapolated reversal potential near approximately +150 mV, which was completely blocked by amiloride (30 μM). Treatment of isolated taste cells with arginine⁸-vasopressin caused equivalent increases in both I_Na and I_H+; each effect was mimicked by 8-Br-cAMP. Taken together, these results indicate that protons permeate amiloride-sensitive Na⁺ channels in hamster fungiform taste cells and contribute to acid transduction.