Lindemann B, Barbry P, Kretz O, Bock R
Department of Physiology, Saar University, Homburg, Germany.
Ann N Y Acad Sci. 1998 Nov 30;855:116-27. doi: 10.1111/j.1749-6632.1998.tb10553.x.
Epithelial Na+ channels (ENaCs) are thought to mediate the amiloride-blockable salt taste. The rat vallate papilla does not contribute to amiloride-blockable salt taste, yet the presence of ENaC-mRNA in this tissue has been reported. Is ENaC actually contained in the taste cells, or is it merely present in the supporting lingual epithelium? To avoid contamination by ENaC contained in the lingual epithelium, we physically isolated taste buds from the vallate papilla and used mRNA purification followed by reverse transcriptase polymerase chain reaction (RT-PCR) to investigate the presence of ENaC-type message in the isolated buds. mRNA of alpha-, beta- and gamma-subunits was detected, the alpha-signal being the strongest. These results provide first molecular evidence for the presence of ENaC subunits in taste buds that were isolated from the posterior tongue and were free of epithelial contamination. In addition, we used immunohistochemistry to show ENaC-like reactivity in posterior tongue taste cells. Interestingly, the immunoreactivity was not predominantly apical but was intracellular and close to or at the basolateral membrane. The function of basolateral ENaC-type channels is unknown. Possibly, the channels are normally closed or of very low open probability in the resting state.
上皮钠离子通道（ENaCs）被认为介导了amiloride可阻断的盐味。大鼠轮廓乳头对amiloride可阻断的盐味没有贡献，但该组织中已报道存在ENaC-mRNA。ENaC实际上是否存在于味觉细胞中，还是仅仅存在于支持性舌上皮中？为避免舌上皮中所含的ENaC造成污染，我们从轮廓乳头中物理分离出味蕾，并使用mRNA纯化，随后进行逆转录聚合酶链反应（RT-PCR），以研究分离出的味蕾中ENaC型信息的存在情况。检测到了α、β和γ亚基的mRNA，α信号最强。这些结果首次提供了分子证据，证明从后舌分离且无上皮污染的味蕾中存在ENaC亚基。此外，我们使用免疫组织化学方法显示后舌味觉细胞中存在ENaC样反应性。有趣的是，免疫反应性并非主要位于顶端，而是位于细胞内，靠近或位于基底外侧膜。基底外侧ENaC型通道的功能尚不清楚。可能这些通道在静息状态下通常是关闭的，或者开放概率非常低。
