Acid-sensing ion channels in taste buds.
Taste receptor cells detect gustatory stimuli using a complex arrangement of ion channels, G protein-coupled receptors, and signaling cascades. Sour and salty tastes are detected by ion channels in the rat. Using a combination of homology screening and functional expression approaches, we screened a rat circumvallate papilla cDNA library and identified acid-sensing ion channel-2a (ASIC2a) and ASIC2b as candidates for the rat sour-sensing channels. In situ hybridization and reverse transcription-polymerase chain reaction experiments revealed that ASIC2a and ASIC2b transcripts were localized in taste bud cells. Immunohistochemistry and immunoprecipitation also revealed that both subunits were expressed in a subset of taste cells and that some of the cells expressed ASIC2a/ASIC2b heteromeric assemblies. Electrophysiological studies demonstrated that stimulation of acetic acid produced larger ASIC2 currents than did hydrochloric acid at the same pH. ASIC2a/ ASIC2b channels generated maximal inward currents at pH <or= 2.0, which agrees well with the in vivo pH-sensitivity of rat taste cells. The amiloride-sensitivity of ASIC2a/ ASIC2b heteromer lessened with decreasing pH and almost completely disappeared at pH 2.0. These data suggest that ASIC2a and ASIC2b may play roles in sour taste transduction.
Shimada
Shoichi
S
Department of Molecular Morphology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan. sshimada@med.nagoya-cu.ac.jp
Ueda
Takashi
T
Ishida
Yusuke
Y
Yamamoto
Takashi
T
Ugawa
Shinya
S
D062565:Acid Sensing Ion Channels; D000818:Animals; D007473:Ion Channels / Q000378:metabolism* / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D051381:Rats; D015222:Sodium Channels / Q000502:physiology*; D013650:Taste Buds / Q000378:metabolism* / Q000502:physiology*
D062565:Acid Sensing Ion Channels; D007473:Ion Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015222:Sodium Channels