Research in taste disorder and development of taste modulators

酸感离子通道-2a （ASIC2a）是一种可被酰胺阻断的质子门控阳离子通道，可能与大鼠味觉细胞的酸味检测有关。为了分离另一种酸味受体亚型，我们筛选了一个大鼠环状乳头cDNA文库，并鉴定了ASIC2a的n端剪接变体ASIC2b，逆转录聚合酶链反应分析证实了ASIC2b转录本在环状乳头中表达，并且在叶状和真菌状乳头中表达。免疫组织化学分析显示，ASIC2b和ASIC2a在环形、叶状和真菌状乳头的味觉细胞亚群中表达，一些细胞同时表现出ASIC2a和ASIC2b的免疫反应性。随后用环形乳头提取物进行的共免疫沉淀研究表明，ASIC2b与ASIC2a结合形成组装体，并结合我们的免疫组织化学发现，强烈表明ASIC2亚基在环形、叶状和真菌状乳头的味觉细胞中形成异质通道。卵母细胞电生理结果表明，ASIC2a/ASIC2b通道在pH值2.0时产生最大的向内电流，这与大鼠味觉细胞的体内pH敏感性很好地吻合，并且异源异构体的阿米酰胺敏感性随着pH值的降低而降低，在pH值2.0时几乎完全消失。这些发现为大鼠味觉细胞对酸诱导反应的阿米洛利不敏感提供了有说服力的解释。

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.