Yoshida R, Horio N, Murata Y, Yasumatsu K, Shigemura N, Ninomiya Y
Section of Oral Neuroscience, Graduate School of Dental Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Fukuoka, Japan.
Neuroscience. 2009 Mar 17;159(2):795-803. doi: 10.1016/j.neuroscience.2008.12.052. Epub 2009 Jan 3.
Previous studies have demonstrated that rodents' chorda tympani (CT) nerve fibers responding to NaCl can be classified according to their sensitivities to the epithelial sodium channel (ENaC) blocker amiloride into two groups: amiloride-sensitive (AS) and -insensitive (AI). The AS fibers were shown to respond specifically to NaCl, whereas AI fibers broadly respond to various electrolytes, including NaCl. These data suggest that salt taste transduction in taste cells may be composed of at least two different systems; AS and AI ones. To further address this issue, we investigated the responses to NaCl, KCl and HCl and the amiloride sensitivity of mouse fungiform papilla taste bud cells which are innervated by the CT nerve. Comparable with the CT data, the results indicated that 56 NaCl-responsive cells tested were classified into two groups; 25 cells ( approximately 44%) narrowly responded to NaCl and their NaCl response were inhibited by amiloride (AS cells), whereas the remaining 31 cells ( approximately 56%) responded not only to NaCl, but to KCl and/or HCl and showed no amiloride inhibition of NaCl responses (AI cells). Amiloride applied to the basolateral side of taste cells had no effect on NaCl responses in the AS and AI cells. Single cell reverse transcription-polymerase chain reaction (RT-PCR) experiments indicated that ENaC subunit mRNA was expressed in a subset of AS cells. These findings suggest that the mouse fungiform taste bud is composed of AS and AI cells that can transmit taste information differently to their corresponding types of CT fibers, and apical ENaCs may be involved in the NaCl responses of AS cells.
以往的研究表明，啮齿动物的鼓索神经（CT）中对氯化钠有反应的神经纤维可根据其对上皮钠通道（ENaC）阻断剂氨氯吡咪的敏感性分为两组：氨氯吡咪敏感（AS）组和不敏感（AI）组。研究显示，AS纤维对氯化钠有特异性反应，而AI纤维对包括氯化钠在内的各种电解质都有广泛反应。这些数据表明，味觉细胞中的盐味转导可能至少由两种不同的系统组成；即AS系统和AI系统。为了进一步探讨这个问题，我们研究了由CT神经支配的小鼠菌状乳头味蕾细胞对氯化钠、氯化钾和盐酸的反应以及氨氯吡咪敏感性。与CT神经的数据相似，结果表明，所检测的56个对氯化钠有反应的细胞分为两组；25个细胞（约44%）对氯化钠反应狭窄，其对氯化钠的反应被氨氯吡咪抑制（AS细胞），而其余31个细胞（约56%）不仅对氯化钠有反应，还对氯化钾和/或盐酸有反应，且对氯化钠的反应未表现出氨氯吡咪抑制（AI细胞）。将氨氯吡咪应用于味觉细胞的基底外侧对AS和AI细胞的氯化钠反应没有影响。单细胞逆转录聚合酶链反应（RT-PCR）实验表明，ENaC亚基mRNA在一部分AS细胞中表达。这些发现表明，小鼠菌状味蕾由AS细胞和AI细胞组成，它们可以将味觉信息以不同方式传递给相应类型的CT神经纤维，顶端的ENaC可能参与了AS细胞对氯化钠的反应。
