Extracellular acid block and acid-enhanced inactivation of the Ca2+-activated cation channel TRPM5 involve residues in the S3-S4 and S5-S6 extracellular domains
Extracellular acid block and acid-enhanced inactivation of the Ca2+-activated cation channel TRPM5 involve residues in the S3-S4 and S5-S6 extracellular domains
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DOI：
10.1074/jbc.m414072200
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发表时间：
2005-05-27
影响因子：
4.8
通讯作者：
Liman, ER
中科院分区：
文献类型：
--
作者：
Liu, D;Zhang, Z;Liman, ER
TRPM 5是瞬时受体电位离子通道超家族的成员，对于检测苦、甜和氨基酸味道是必需的。在异源细胞类型中，它形成由细胞内Ca 2+激活的非选择性阳离子通道。TRPM 5可能是味觉传导级联的一部分，并且TRPM 5的调节剂可能影响味觉。在这份报告中，我们表明，TRPM 5，而不是相关的通道TRPM 4 b，是有力的细胞外酸化阻断。外部酸化有两种作用，快速可逆阻断电流（IC 50 pH = 6.2）和较慢的不可逆增强电流失活。S3-S4接头中的单个Glu残基和孔区域中的His残基的突变各自降低TRPM 5电流对快速酸阻断的敏感性（两者的IC 50 pH = 5.8），并且双突变体对酸性pH几乎不敏感（IC 50 pH = 5.0）。长期暴露于酸性pH增强TRPM 5电流的失活，和突变体通道，酸阻断不太敏感，也不太敏感的酸增强失活，这表明两个过程之间的密切关联。然而，这些过程是不同的，因为孔突变体H896 N，它具有正常的敏感性，酸封闭，显示显着恢复酸增强失活。这些数据表明，细胞外酸化通过TRPM 5上的特定残基起作用，通过两种不同但相关的机制阻断传导，并表明细胞外pH与苦、甜和氨基酸味觉转导的激活和适应之间可能存在相互作用。
TRPM5, a member of the superfamily of transient receptor potential ion channels, is essential for the detection of bitter, sweet, and amino acid tastes. In heterologous cell types it forms a nonselective cation channel that is activated by intracellular Ca2+. TRPM5 is likely to be part of the taste transduction cascade, and regulators of TRPM5 are likely to affect taste sensation. In this report we show that TRPM5, but not the related channel TRPM4b, is potently blocked by extracellular acidification. External acidification has two effects, a fast reversible block of the current (IC50 pH = 6.2) and a slower irreversible enhancement of current inactivation. Mutation of a single Glu residue in the S3-S4 linker and a His residue in the pore region each reduced sensitivity of TRPM5 currents to fast acid block (IC50 pH = 5.8 for both), and the double mutant was nearly insensitive to acidic pH (IC50 pH = 5.0). Prolonged exposure to acidic pH enhanced inactivation of TRPM5 currents, and mutant channels that were less sensitive to acid block were also less sensitive to acid-enhanced inactivation, suggesting an intimate association between the two processes. These processes are, however, distinct because the pore mutant H896N, which has normal sensitivity to acid block, shows significant recovery from acid-enhanced inactivation. These data show that extracellular acidification acts through specific residues on TRPM5 to block conduction through two distinct but related mechanisms and suggest a possible interaction between extracellular pH and activation and adaptation of bitter, sweet, and amino acid taste transduction.