| Co-Investigator(Kenkyū-buntansha) |
UEDA Takashi Nagoya City University, Graduate School of Medical Sciences, Research Associate, 大学院・医学研究科, 助手 (90244540)
HIRABAYASHI Yoshifumi Nagoya City University, Graduate School of Medical Sciences, Assistant Professor, 大学院・医学研究科, 講師 (30181184)
MURAKAMI Shingo Nagoya City University, Graduate School of Medical Sciences, Professor, 大学院・医学研究科, 教授 (80157750)
UGAWA Shinya Nagoya City University, Graduate School of Medical Sciences, Research Associate, 大学院・医学研究科, 助手 (20326135)
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| Research Abstract |
Acid-sensing ion channel-2a (ASIC2a) is an amiloride-blockable proton-gated cation channel, probably contributing to sour-taste detection in rat taste cells. To isolate another subtype of the sour-taste receptor, we screened a rat circumvallate papilla cDNA library and identified ASIC2b, an N-terminal splice variant of ASIC2a, Reverse transcription-polymerase chain reaction analyses confirmed the expression of ASIC2b transcripts in the circumballate papilla and, moreover, demonstrated its expression in the foliate and fungiform papillae. Immunohistochemical analyses revealed that ASIC2b, as well as ASIC2a, was expressed in a subpopulation of taste cells in the circumvallate, foliate, and fungiform papillae, and some of the cells displayed both ASIC2a-and ASIC2b-immunoreactivities. Subsequent co-immunoprecipitation studies with circumvallate papillae extracts indicated that ASIC2b associated with ASIC2a to form assemblies, and, together with our immunohistochemical findings, strongly suggested that both ASIC2 subunits formed heteromeric channels in taste cells in the circumvallate, foliate, and fungiform papillae. Oocyte electrophysiology demonstrated that the ASIC2a/ASIC2b channel generated maximal in ward currents at pH 2.0, which is in good agreement with the in vivo pH-sensitivity of rat taste cells, and that the amiloride-sensitivity of the heteromer decreased with decreasing pH and was almost completely abolished at pH 2.0. These findings provide persuasive explanations for the amiloride-insensitivity of acid-induced responses of rat taste cells.
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