Abstract
Amiloride-sensitive epithelial Na+ channels (ENaCs) are proposed to be involved in salt taste transduction. Electrophysiological studies in C57BL/6 (B6) mice demonstrated that responses to NaCl are inhibited by amilolide in the choda tympani (CT) but not in the glossopharyngeal nerve, suggesting a lack of amiloride sensitivity (AS) in the posterior tongue. The AS also differs among inbred mouse strains. Unlike B6 mice, 129P3/J (129) mice showed almost no amiloride inhibition of NaCl responses even in the CT. In this study, using B6, 129 mice and their F2 hybrids, we examined possible relationships of the AS with mRNA expression levels in fungiform papillae (FP) and single nucleotide polymorphisms (SNPs) of three subunits of ENaC (α,β,γ). The mRNA expression levels of each ENaC subunit examined using RT-PCR analysis were similar in the B6 and 129 strains. Sequencing detected three SNPs in the α-subunit. One of these SNPs resulted in an amino acid substitution, R616W, near the predicted 2nd transmembrane domain in the 129 strain. No SNPs were found in sequences of β- and γ-subunits. Electrophysiological and sequencing analyses in F2 hybrids indicated that there was no relation between the AS and the α-subunit SNP (R616W). These results suggest that neither expression levels of the three ENaC subunits, nor the SNP in the α-subunit participate in the mouse strain differences in the AS. [Jpn J Physiol 55 Suppl:S166 (2005)]
