Amiloride-Insensitive Currents of the Acid-Sensing Ion Channel-2a (ASIC2a)/ASIC2b Heteromeric Sour-Taste Receptor Channel
Amiloride-Insensitive Currents of the Acid-Sensing Ion Channel-2a (ASIC2a)/ASIC2b Heteromeric Sour-Taste Receptor Channel
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DOI：
10.1523/jneurosci.23-09-03616.2003
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发表时间：
2003-05
期刊：
影响因子：
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通讯作者：
S. Ugawa;Takashi Yamamoto;T. Ueda;Y. Ishida;A. Inagaki;Makoto Nishigaki;S. Shimada
中科院分区：
文献类型：
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作者：
S. Ugawa;Takashi Yamamoto;T. Ueda;Y. Ishida;A. Inagaki;Makoto Nishigaki;S. Shimada
酸敏感离子通道-2a（ASIC 2a）是一种可被阿米洛利阻断的质子门控阳离子通道，可能参与大鼠味觉细胞的酸味检测。为了分离酸味受体的另一种亚型，我们筛选了大鼠轮廓乳头cDNA文库，并确定了ASIC 2b，ASIC 2a的N-末端剪接变体。逆转录-PCR分析证实了ASIC 2b转录本在轮廓乳头的表达，而且，证明了其在叶状和菌状乳头的表达。免疫组织化学分析显示，ASIC 2b，以及ASIC 2a，在轮廓，叶状，菌状乳头的味觉细胞的亚群中表达，和一些细胞显示ASIC 2a和ASIC 2b免疫反应。随后对轮廓乳头提取物的免疫共沉淀研究表明，ASIC 2b与ASIC 2a结合形成组装体，并且结合我们的免疫组织化学发现，强烈表明两个ASIC 2亚基在轮廓乳头、叶状乳头和菌状乳头的味觉细胞中形成了异聚体通道。卵母细胞电生理结果表明，ASIC 2a/ASIC 2b通道在pH ≤2.0时产生最大内向电流，这与大鼠味觉细胞的体内pH敏感性一致，并且异聚体的阿米洛利敏感性随着pH的降低而降低，并且在pH 2.0时几乎完全消除。这些发现提供了有说服力的解释阿米洛利不敏感的酸诱导反应的大鼠味觉细胞。
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-PCR analyses confirmed the expression of ASIC2b transcripts in the circumvallate 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 coimmunoprecipitation 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 inward currents at a pH of ≤2.0, which is in 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 a pH of 2.0. These findings provide persuasive explanations for the amiloride insensitivity of acid-induced responses of rat taste cells.