Amiloride-sensitive NaCl taste responses are associated with genetic variation of ENaC alpha-subunit in mice

An epithelial Na+ channel (ENaC) is expressed in taste cells and may be involved in the salt taste transduction. ENaC activity is blocked by amiloride, which in several mammalian species also inhibits taste responses to NaCl. In mice, lingual application of amiloride inhibits NaCl responses in the chorda tympani (CT) gustatory nerve much stronger in the C57BL/6 (B6) strain than in the 129P3/J (129) strain. We examined whether this strain difference is related to gene sequence variation or mRNA expression of three ENaC subunits (alpha, beta, gamma). Real-time RT-PCR and in situ hybridization detected no significant strain differences in expression of all three ENaC subunits in fungiform papillae. Sequences of the beta- and gamma ENaC subunit genes were also similar in the B6 and 129 strains, but alpha ENaC gene had three single nucleotide polymorphisms (SNPs). One of these SNPs resulted in a substitution of arginine in the B6 strain to tryptophan in the 129 strain (R616W) in the alpha ENaC protein. To examine association of this SNP with amiloride sensitivity of CT responses to NaCl, we produced F2 hybrids between B6 and 129 strains. Amiloride inhibited CT responses to NaCl in F-2 hybrids with B6/129 and B6/B6 alpha ENaC R616W genotypes stronger than in F-2 hybrids with 129/129 genotype. This suggests that the R616W variation in the alpha ENaC subunit affects amiloride sensitivity of the ENaC channel and provides evidence that ENaC is involved in amiloride-sensitive salt taste responses in mice.