摘要
Taste cells located in taste buds respond to gustatory stimuli using a complex arrangement of ion channels, receptor molecules and signaling cascades. Previous electrophysiological experiments have shown that sour taste (essentially a taste of protons) is mediated, at least in part, by apically located amiloride-sensitive channels in the rat. Here, the molecular cloning of sour-taste receptor genes is described. 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, amiloride-sensitive proton-activated cation channels. In situ hybridization and reverse transcription-polymerase chain reaction experiments showed that ASIC2a and ASIC2b transcripts were localized in taste cells. Immunohistochemical and immunoprecipitation studies revealed that both channels were expressed in a subset of taste cells and that some of the cells expressed ASIC2a/ASIC2b heteromeric assemblies. Immunoelectron microscopic analyses demonstrated that some of the ASIC2a-immunopositive cells had the characteristics of type III cells, which make synaptic contacts with gustatory afferent neurons. According to our electrophysiological studies, stimulation by acetic acid generated larger inward currents in ASIC2a- or ASIC2a/ASIC2b-expressing oocytes than those induced by hydrochloric acid at the same proton concentration and these findings are in good agreement with the well-known taste phenomenon that acetic acid is more sour than hydrochloric acid at equal pH. Taken together, the present results strongly suggest that mucosal protons dissociated from sour-taste substances induce taste cell depolarization through the activation of the ASIC2a and ASIC2a/ASIC2b channels, which leads to transmitter release onto gustatory neurons.
摘要译文
位于味蕾味细胞使用的离子通道，受体分子和信号级联的复杂排列味觉刺激作出反应。先前电生理实验已经表明，酸味（质子的本质上是味道）介导的，至少部分地由顶部位于阿米洛利敏感通道在大鼠。这里，酸酸的，味道受体基因的分子克隆描述。使用同源性筛选和功能表达方法的组合，我们筛选大鼠circumvallate乳头cDNA文库鉴定酸敏感离子通道2a中（ASIC2a）和ASIC2b，阿米洛利敏感质子激活的阳离子通道。原位杂交和逆转录 - 聚合酶链反应的实验表明，ASIC2a和ASIC2b转录物定位在味觉细胞。免疫组化和免疫沉淀研究表明，这两个信道进行了表达味觉细胞的一个子集，并且一些表达ASIC2a / ASIC2b异聚体的细胞。免疫电子显微镜分析表明，部分ASIC2a免疫阳性细胞具有III型细胞的特性，这使得与味觉传入神经元突触联系。根据我们的电生理研究，在相同的质子浓度土木工程署由盐酸和这些发现与公知的味道现象乙酸比盐酸以相等的pH更酸很好的一致性。两者合计，本结果强烈表明粘膜质子从酸味口味物质通过ASIC2a和ASIC2a / ASIC2b通道的活化诱导味细胞去极化解离这导致递质释放到味觉神经元。
Shinya Ugawa [1]. Identification of sour-taste receptor genes[J]. Anatomical Science International, 2003,78(4): 205-210