Institute of Cell Biophysics, Russian Academy of Sciences, Institutional Street 3, Pushchino, Moscow Region, 142290, Russia.
J Cell Sci. 2010 Mar 15;123(Pt 6):972-82. doi: 10.1242/jcs.061879. Epub 2010 Feb 23.
Three types of morphologically and functionally distinct taste cells operate in the mammalian taste bud. We demonstrate here the expression of two G-protein-coupled receptors from the family C, CASR and GPRC6A, in the taste tissue and identify transcripts for both receptors in type I cells, no transcripts in type II cells and only CASR transcripts in type III cells, by using the SMART-PCR RNA amplification method at the level of individual taste cells. Type I taste cells responded to calcimimetic NPS R-568, a stereoselective CASR probe, with Ca(2+) transients, whereas type I and type II cells were not specifically responsive. Consistent with these findings, certain amino acids stimulated PLC-dependent Ca(2+) signaling in type III cells, but not in type I and type II cells, showing the following order of efficacies: Phe~Glu>Arg. Thus, CASR is coupled to Ca(2+) mobilization solely in type III cells. CASR was cloned from the circumvallate papilla into a pIRES2-EGFP plasmid and heterologously expressed in HEK-293 cells. The transfection with CASR enabled HEK-293 cells to generate Ca(2+) transients in response to the amino acids, of which, Phe was most potent. This observation and some other facts favor CASR as the predominant receptor subtype endowing type III cells with the ability to detect amino acids. Altogether, our results indicate that type III cells can serve a novel chemosensory function by expressing the polymodal receptor CASR. A role for CASR and GPRC6A in physiology of taste cells of the type I remains to be unveiled.
哺乳动物味蕾中有三种形态和功能不同的味觉细胞。我们在此证明，两种 C 族 G 蛋白偶联受体，即钙敏感受体（CASR）和 GPRC6A，在味觉组织中表达，并通过 SMART-PCR RNA 扩增方法在单个味觉细胞水平上鉴定出这两种受体的转录本在 I 型细胞中存在，在 II 型细胞中不存在，而仅在 III 型细胞中存在 CASR 转录本。I 型味觉细胞对钙敏感受体探针 NPS R-568 （一种立体选择性的 CASR 探针）产生 Ca2+瞬变反应，而 I 型和 II 型细胞则没有特异性反应。这些发现与以下结果一致：某些氨基酸刺激 III 型细胞而不刺激 I 型和 II 型细胞产生 PLC 依赖性 Ca2+信号，其效力顺序为：Phe~Glu>Arg。因此，CASR 仅在 III 型细胞中与 Ca2+动员偶联。我们从轮廓乳头克隆了 CASR 并将其插入 pIRES2-EGFP 质粒中，然后在 HEK-293 细胞中异源表达。转染 CASR 使 HEK-293 细胞能够对氨基酸产生 Ca2+瞬变反应，其中 Phe 最有效。这一观察结果和其他一些事实支持 CASR 作为赋予 III 型细胞检测氨基酸能力的主要受体亚型。总之，我们的结果表明，III 型细胞可以通过表达多模态受体 CASR 发挥新的化学感觉功能。CASR 和 GPRC6A 在 I 型味觉细胞生理学中的作用仍有待揭示。
