Amiloride suppression of the taste intensity of sodium chloride: evidence from direct magnitude scaling.

The transduction of Na+ salts has been shown in many species to be mediated in part by an epithelial ion channel on the apical surface of the taste receptor cell membrane, which is blockable by the diuretic amiloride. In addition to this apical ion channel, Na+ is also transduced via a paracellular pathway, which is not sensitive to amiloride. There are significant species differences in the contribution of the amiloride-sensitive pathway to Na+ transduction. Previous human psychophysical studies have reported conflicting results on the effects of amiloride in suppressing the intensity of NaCl. In general, these studies used amiloride doses that were much higher than those showing clear suppressive effects in electrophysiological studies in other species. In the present experiment, we used direct magnitude scaling of the intensities of five NaCl concentrations flowed over the anterior portion of the tongue to determine the effects of amiloride treatment at lower doses. NaCl was presented after adaptation of the tongue to water or mixed with and presented after adaptation to 10, 50, or 100 microM amiloride-HCl. Subjects estimated the intensity of NaCl and of these concentrations of amiloride in each treatment condition using magnitude estimation with a 0.1 M NaCl modulus presented following a water rinse prior to each session. Results showed that amiloride had a significant suppressive effect on the perceived intensity of NaCl, with a similar effect seen at all three amiloride doses. The psychophysical function after amiloride showed a parallel shift to the right. The average suppression over all NaCl concentrations was 21%.(ABSTRACT TRUNCATED AT 250 WORDS)