Inhibition by amiloride of chorda tympani responses evoked by monovalent salts

The diuretic, amiloride, is a potent yet reversible inhibitor of passive sodium transport in many epithelia. It has been shown to inhibit sodium transport in dorsal lingual epithelia and to inhibit both psychophysical and neural measures of salt taste. The present results demonstrate that amiloride's action as an inhibitor of integrated whole chorda tympani nerve recordings in the rat is specific for Li and Na salts, displaying little inhibition of neural responses evoked by KCl and RbCl. Amiloride reduces both the phasic and tonic portion of the nerve recording equally. When amiloride inactivates the tonic portion of the nerve response to 250 mM NaCl, only a portion of the response is affected. Complete inactivation does not occur even at high amiloride concentrations. With amiloride flowing constantly over the tongue at 1 microM, 10 microM, or 50 microM a reciprocal plot of stimulus NaCl concentration versus response is non-linear. This result suggests that the inhibition of the NaCl-induced response has both competitive and non-competitive properties. These results support the hypothesis that salt taste is mediated in part by amiloride sensitive Na-channels located in taste receptor cell plasma membranes.