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1 Department of Psychology and Center for Smell and Taste, University of Florida, Gainesville, Florida, United States
2 Department of Physiology, Virginia Commonwealth University, Richmond, Virginia, United States
* To whom correspondence should be addressed. E-mail: spector{at}ufl.edu.
Current evidence suggests salt taste transduction involves at least two mechanisms, one that is amiloride-sensitive and appears to utilize apically located epithelial sodium channels relatively selective for Na+ and a second that is amiloride-insensitive and utilizes a variant of the transient receptor potential vanilloid receptor 1 (TRPV1) that serves as a non-specific cation channel. To provide a functional context for these findings, we trained Trpv1 KO and WT C57BL/6J mice (n=9-10/group) in a two-response operant discrimination procedure and measured detection thresholds to NaCl and KCl with and without amiloride. The KO and WT mice had similar detection thresholds for NaCl and KCl. Amiloride shifted the NaCl sensitivity curve to the same degree in both groups and had virtually no effect on KCl thresholds. In addition, a more detailed analysis of chorda tympani nerve (CT) responses to NaCl, with and without benzamil (Bz, an amiloride analogue) treatment revealed that the tonic portion of the CT response of KO mice to NaCl + Bz was absent, but both KO and WT mice displayed some degree of a phasic response to NaCl with and without Bz. Because these transients constitute the entire CT response to NaCl + Bz in Trpv1 KO mice, it is possible that these signals are sufficient to maintain normal NaCl detectabilty in the behavioral task used here. Additionally, there may be other amiloride-insensitive salt transduction mechanisms in taste receptor fields other than the anterior tongue that maintain normal salt detection performance in the KO mice.
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