Amiloride suppresses the sourness of NaCl and LiCl

The transduction of Na+ salts in many species is mediated by both apical and submucosal ion channels on the taste receptor-cell membrane. The apical ion channel is blockable by the diuretic amiloride, whereas the submucosal pathway is not. Previous human psychophysical studies have shown a decrease in NaCl taste intensity caused by amiloride that is smaller than the reduction of the electrophysiological response produced by amiloride in other species. Many salts, including NaCl, elicit not only a salty taste to humans, but also sweet, sour, or bitter side tastes. Amiloride has been shown to reduce the sourness, but not the saltiness, of NaCl and Na gluconate and to have no effect on the taste of KCl. The present experiment further evaluated the hypothesis that the sour taste of Na+ and Li+ salts is mediated by the amiloride-sensitive transduction mechanism, by examining the effect of amiloride on the taste of LiCl, which is considerably more sour than NaCl. Four concentrations of NaCl, LiCl, and KCl were presented to the anterior tongue following adaptation to water or after 10 microM amiloride treatment. Subjects estimated the intensity of the taste of each stimulus and divided this estimate among the appropriate taste qualities. There was a significant decrease in the total taste intensity of NaCl and LiCl after amiloride, but no effect on KCl; LiCl was more greatly suppressed than NaCl. These data show no effect on the saltiness of LiCl or NaCl, except for a small reduction in the saltiness of 0.1 M NaCl. On the contrary, there was a significant effect on the sourness of both NaCl and LiCl. Citric acid (3.2 mM) was also used as a stimulus, but amiloride treatment had no effect on its sourness. These data indicate that the amiloride-sensitive channel plays a key role in the perception of the sour taste of NaCl and LiCl (but not citric acid) and little role in the perception of saltiness. The salty taste of these salts may arise from other transduction pathways.