Department of Oral Biology, University of Manitoba, Winnipeg, MB, Canada R3E 0W2.
Biochem Biophys Res Commun. 2011 Mar 4;406(1):146-51. doi: 10.1016/j.bbrc.2011.02.016. Epub 2011 Feb 12.
Humans are capable of sensing five basic tastes which are sweet, sour, salt, umami and bitter. Of these, bitter taste perception provides protection against ingestion of potentially toxic substances. Bitter taste is sensed by bitter taste receptors (T2Rs) that belong to the G-protein coupled receptors (GPCRs) superfamily. Humans have 25 T2Rs that are expressed in the oral cavity, gastrointestinal (GI) neuroendocrine cells and airway cells. Electrophysiological studies of the brain neurons show that the neurons are able to respond to different tastants. However, the presence of bitter taste receptors in brain cells has not been elucidated. In this report using RT-PCR, and immunohistochemistry analysis we show that T2Rs are expressed in multiple regions of the rat brain. RT-PCR analysis revealed the presence of T2R4, T2R107 and T2R38 transcripts in the brain stem, cerebellum, cortex and nucleus accumbens. The bitter receptor T2R4 was selected for further analysis at the transcript level by quantitative real time PCR and at the protein level by immunohistochemistry. To elucidate if the T2R4 expressed in these cells is functional, assays involving G-protein mediated calcium signaling were carried out. The functional assays showed an increase in intracellular calcium levels after the application of exogenous ligands for T2R4, denatonium benzoate and quinine to these cultured cells, suggesting that endogenous T2R4 expressed in these cells is functional. We discuss our results in terms of the physiological relevance of bitter receptor expression in the brain.
人类能够感知五种基本味道，分别是甜、酸、咸、鲜和苦。其中，苦味感知为我们提供了保护，使我们避免摄入潜在的有毒物质。苦味是由苦味受体（T2R）感知的，这些受体属于 G 蛋白偶联受体（GPCR）超家族。人类有 25 种 T2R，这些受体在口腔、胃肠道（GI）神经内分泌细胞和气道细胞中表达。对大脑神经元的电生理研究表明，神经元能够对不同的味觉物质做出反应。然而，脑细胞中是否存在苦味受体尚未阐明。在本报告中，我们通过 RT-PCR 和免疫组织化学分析表明，T2R 存在于大鼠大脑的多个区域。RT-PCR 分析显示，T2R4、T2R107 和 T2R38 转录本存在于脑干、小脑、皮质和伏隔核。苦味受体 T2R4 被选择用于进一步的转录水平分析，通过定量实时 PCR，以及蛋白水平分析，通过免疫组织化学。为了阐明这些细胞中表达的 T2R4 是否具有功能，我们进行了涉及 G 蛋白介导的钙信号转导的测定。功能测定显示，外源性 T2R4 配体苯甲地那铵和奎宁应用于这些培养细胞后，细胞内钙水平升高，这表明这些细胞中表达的内源性 T2R4 是有功能的。我们根据苦味受体在大脑中的表达与生理相关性来讨论我们的结果。
