Division of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki 444-8787, Japan.
J Biol Chem. 2010 Jun 4;285(23):17277-81. doi: 10.1074/jbc.C110.132944. Epub 2010 Apr 20.
Five basic tastes (bitter, sweet, umami, salty, and sour) are detected in the four taste areas where taste buds reside. Although molecular mechanisms for detecting bitter, sweet, and umami have been well clarified, those for sour and salty remain poorly understood. Several channels including acid-sensing ion channels have been proposed as candidate sour receptors, but they do not encompass all sour-sensing abilities in vivo. We recently reported a novel candidate for sour sensing, the polycystic kidney disease-2-like 1 (PKD2L1)-PKD1L3 channel complex. This channel is not a traditional ligand-gated channel and is gated open only after removal of an acid stimulus, called an off response. Here we show that off responses upon acid stimulus are clearly observed in native taste cells from circumvallate, but not fungiform papillae, of glutamate decarboxylase 67-green fluorescent protein (GAD67-GFP) knock-in mice, from which Type III taste cells can be visualized, using Ca(2+) imaging and patch clamp methods. Off responses were detected in most cells where PKD2L1 immunoreactivity was observed. Interestingly, the pH threshold for acid-evoked intracellular Ca(2+) increase was around 5.0, a value much higher than that observed in HEK293 cells expressing the PKD2L1-PKD1L3 complex. Thus, PKD2L1-PKD1L3-mediated acid-evoked off responses occurred both in HEK293 cells and in native taste cells, suggesting the involvement of the PKD2L1-PKD1L3 complex in acid sensing in vivo.
五种基本味道（苦、甜、鲜、咸和酸）可在味蕾所在的四个味觉区域中被检测到。尽管检测苦、甜和鲜的分子机制已得到充分阐明，但酸和咸的机制仍知之甚少。已经提出了几种包括酸敏离子通道在内的通道作为候选酸受体，但它们并不能涵盖体内所有的酸感觉能力。我们最近报道了一种新的酸感应候选物，多囊肾病 2 样 1（PKD2L1）-PKD1L3 通道复合物。该通道不是传统的配体门控通道，只有在去除酸刺激后才会打开，称为关闭反应。在这里，我们表明，在用 Ca(2+)成像和膜片钳方法从谷氨酸脱羧酶 67-绿色荧光蛋白 (GAD67-GFP) 敲入小鼠的环咽和菌状乳头中的原生味细胞中，可以清楚地观察到酸刺激后的关闭反应，从中可以可视化 III 型味细胞。在大多数观察到 PKD2L1 免疫反应性的细胞中检测到关闭反应。有趣的是，酸诱发细胞内 Ca(2+)增加的 pH 阈值约为 5.0，这一值远高于在表达 PKD2L1-PKD1L3 复合物的 HEK293 细胞中观察到的值。因此，PKD2L1-PKD1L3 介导的酸诱发关闭反应既发生在 HEK293 细胞中，也发生在原生味细胞中，这表明 PKD2L1-PKD1L3 复合物参与了体内的酸感应。
