Sour (acid) taste is postulated to result from intracellular acidification that modulates one or more acid-sensitive ion channels in taste receptor cells. The identity of such channel(s) remains uncertain. Potassium channels, by regulating the excitability of taste cells, are candidates for acid transducers. Several 2-pore domain potassium leak conductance channels (K2P family) are sensitive to intracellular acidification. We examined their expression in mouse vallate and foliate taste buds using RT-PCR, and detected TWIK-1 and -2, TREK-1 and -2, and TASK-1. Of these, TWIK-1 and TASK-1 were preferentially expressed in taste cells relative to surrounding nonsensory epithelium. The related TRESK channel was not detected, whereas the acid-insensitive TASK-2 was. Using confocal imaging with pH-, Ca2+-, and voltage-sensitive dyes, we tested pharmacological agents that are diagnostic for these channels. Riluzole (500 μM), selective for TREK-1 and -2 channels, enhanced acid taste responses. In contrast, halothane (≤ ∼17 mM), which acts on TREK-1 and TASK-1 channels, blocked acid taste responses. Agents diagnostic for other 2-pore domain and voltage-gated potassium channels (anandamide, 10 μM; Gd3+, 1 mM; arachidonic acid, 100 μM; quinidine, 200 μM; quinine, 100 mM; 4-AP, 10 mM; and TEA, 1 mM) did not affect acid responses. The expression of 2-pore domain channels and our pharmacological characterization suggest that a matrix of ion channels, including one or more acid-sensitive 2-pore domain K channels, could play a role in sour taste transduction. However, our results do not unambiguously identify any one channel as the acid taste transducer.
Acid-sensitive TWIK and TASK Two-pore Domain Potassium Channels Change Ion Selectivity and Become Permeable to Sodium in Extracellular Acidification
