Non-specific inhibition by amiloride of canine chorda tympani nerve responses to various salts: do Na(+)-specific channels exist in canine taste receptor membranes?

In order to test the hypothesis that the taste response to NaCl is induced by entry of Na+ through the apical membranes of taste cells, the effects of amiloride on the canine chorda tympani nerve responses to various stimuli were compared with those on the short-circuit current (Isc) in the presence of salts in an in vitro preparation of the canine lingual epithelium. Application of amiloride to the tongue greatly inhibited the taste nerve responses to NaCl, LiCl, RbCl, CsCl, KCl and NH4Cl. There was no large difference in the amiloride inhibition among these salts. Amiloride also inhibited partly the responses to salts carrying impermeable cations such as choline+ or glycineamide+. Amiloride shifted the dose-response curves for the salt taste responses to a higher concentration region without appreciable effects on the maximal responses, suggesting that amiloride inhibits the salt responses in a competitive manner. It was concluded that the effects of amiloride on the taste nerve responses observed in the present study were quite different from those on Isc. The present results favor a conclusion that in the dog, a competitive binding of amiloride carrying a positive charge to the receptor sites for the cations of the salt stimuli leads to inhibition of the salt responses.