Na⁺-H⁺Exchange Activity in Taste Receptor Cells

Abstract

. mRNA for two Na ϩ -H ϩ -exchanger isoforms 1 and 3 (NHE-1 and NHE-3) was detected by RT-PCR in fungiform and circumvallate taste receptor cells (TRCs). Anti-NHE-1 antibody binding was localized to the basolateral membranes, and the anti-NHE-3 antibody was localized in the apical membranes of fungiform and circumvallate TRCs. In a subset of TRCs, NHE-3 immunoreactivity was also detected in the intracellular compartment. For functional studies, an isolated lingual epithelium containing a single fungiform papilla was mounted with apical and basolateral sides isolated and perfused with nominally CO 2 /HCO 3 Ϫ -free physiological media (pH 7.4). The TRCs were monitored for changes in intracellular pH (pH i ) and Na The results indicate the presence of a functional NHE-1 in the basolateral membranes of TRCs. We hypothesize that NHE-1 is involved in sour taste transduction since its activity is modulated during acid stimulation.

Taste Receptor Genes

“…Based on the gene expression pattern and pharmacological analysis, TASK-1 appears to be the most likely candidate (see TASK-1 sidebar), although other K 2 P channels cannot be excluded (142). The Na + -H + -exchanger isoform 1 (NHE-1) (see NHE-1 sidebar) was also suggested to be involved in sour taste transduction based on its gene expression and pharmacological analyses (165).…”

Signal transduction and information processing in mammalian taste buds

“…2). If present in high enough concentration (i.e., low pH), extracellular protons will also cross the cell membrane, presumably through ion channels and ion exchangers such as the sodium-hydrogen exchanger (found in taste cells [15]), and acidify the cytoplasm, thereby explaining the sour taste of relatively concentrated solutions of HCl and other mineral acids.…”

Taste Receptors in the Gastrointestinal Tract III. Salty and sour taste: sensing of sodium and protons by the tongue

“…Evidence indicates the presence of both conductive proton channels (13,15) and the Na ϩ -H ϩ exchanger, isoform 3 (see Fig. 2) (13,24), in the apical membranes of taste receptor cells. However, only the proton channels appear to be functional (13,15,24).…”

“…2) (13,24), in the apical membranes of taste receptor cells. However, only the proton channels appear to be functional (13,15,24). The H ϩ flux through taste receptor cell apical membrane proton channels, as well as the neural response to HCl (but not to CO 2 or acetic acid), is blocked by the divalent metal ions Zn 2ϩ or Cd 2ϩ (unpublished observations).…”