TMC4 localizes to multiple taste cell types in the mouse taste papillae

Salty taste is mediated through two distinct transduction pathways: the
amiloride-sensitive and amiloride-insensitive (AI). Transmembrane
channel-like 4 (TMC4), a voltage-dependent chloride channel, has recently
been identified as playing a critical role in AI-mediated salt taste
responses. Although its functional properties have been demonstrated, the
specific taste cell types that express TMC4 have not been fully
characterized. To investigate the cellular localization of TMC4, we
generated Tmc4-EGFP knock-in mice and performed immunohistochemical
analyses of the taste papillae. By performing multiple fluorescent
immunostaining with cell-type-specific markers, such as KCNQ1 (type
I–III), Gustducin and PLCβ2 (type II), and AADC (type III), together with
EGFP, we found that over 98% of EGFP-positive cells overlapped with the
signal of all three taste cell type markers in the circumvallate papillae
of Tmc4-EGFP mice. In the fungiform papillae, 95.9% of EGFP-positive cells
co-localized with KCNQ1. These results demonstrate that TMC4 is broadly
expressed across all three taste cell types, and suggest the possible
involvement of multiple, functionally distinct taste cell populations in
AI-mediated salty taste transduction.