Illuminating the structure and function of Type I taste cells

摘要 味蕾是报告味觉的多细胞传感器，它反映了潜在的质量和潜在的毒性。 食品构成味蕾的3种细胞类型中的两种（II型和III型）在以下方面得到了充分描述： 不同味觉品质的转导和传递的分子特征，而I型细胞是 被描述为支持性的或神经胶质样的。在这个提议中，我们测试了I型味觉细胞服务于 两个关键功能。首先，我们对味蕾的初步重建表明，I型细胞完全 在味蕾中包围并分隔其他类型的细胞;因此I型细胞对于信号传导和 味蕾信息的整合。其次，我们的超微结构分析进一步表明，一些 I型细胞通过味孔延伸出一个顶突，以采集口腔内容物， 咸味的一些成分。我们建议使用相关的解剖，功能和分子手段， 对小鼠味蕾中的I型细胞进行分类和表征。第一组实验将扩展我们的 初步分析轮廓味蕾中的I型细胞，以测试菌状味觉中的I型细胞是否 芽类似地将II型和III型细胞彼此分开。我们进一步测试I型细胞是否 通过释放GABA或其他神经递质响应释放的ATP参与芽内信号传导 通过刺激的II型（甜-苦-鲜）细胞。然后GABA可以作用于邻近的II型细胞， 信号传导并降低随后对促味剂的反应性。在目标2中，我们测试是否有任何形态 I型细胞的亚型表达功能性阿米洛利敏感性盐（ENaC）受体，如果是这样， 这些细胞与感觉神经纤维的关系。常规EM表明I型细胞不形成 突触留下开放的问题，任何I型细胞的反应如何可以传达到神经 系统我们认为，I型细胞，如中枢神经系统中的神经胶质细胞，可以通过逆转神经递质的释放， GABA或谷氨酸的膜转运蛋白或大孔通道的打开。最后我们会有 解决了两个重要的问题，在转导和传输的味觉信息，通过定义的性质， 受体细胞类型之间的芽内信号传导，其次最终确定细胞的身份， 阿米洛利敏感性盐转导。

Abstract Taste buds are multicellular sensors reporting taste, which reflects quality and potential toxicity for potential food items. Two of the 3 cell types (Type II and Type III) comprising a taste bud are well described in terms of molecular features for transduction and transmission of different taste qualities whereas Type I cells are described as being supporting or glial-like. In this proposal we test the hypothesis that Type I taste cells serve two critical functions. First, our preliminary reconstructions of taste buds show that Type I cells completely surround and separate other cell types in a taste bud; thus Type I cells must be important for signaling and integration of taste information within the bud. Second, our ultrastructural analysis further shows that some Type I cells extend an apical process through the taste pore to sample the oral contents and so may transduce some components of salty taste. We propose to use correlated anatomical, functional and molecular means to classify and characterize Type I cells in taste buds from mice. The first set of experiments will extend our preliminary analysis of Type I cells in circumvallate taste buds to test whether Type I cells in fungiform taste buds similarly separate Type II and Type III cells from one another. Further we test whether the Type I cells participate in intrabud signaling by releasing GABA or other neurotransmitters in response to the ATP released by stimulated Type II (sweet-bitter-umami) cells. The GABA can then act on adjacent Type II cells to terminate signaling and reduce subsequent responsiveness to tastants. In Aim 2, we test whether any morphological subtype of Type I cells expresses functional amiloride-sensitive salt (ENaC) receptors and if so, determine the relationship of these cells to sensory nerve fibers. Conventional EM indicates that Type I cells do not form synapses leaving open the question of how any Type I cell response could be communicated to the nervous system. We suggest that Type I cells, like glial cells in the CNS, can release neurotransmitter by reversal of membrane transporters for GABA or glutamate or opening of large pore channels. In the end we will have resolved two important questions in transduction and transmission of taste information by defining the nature of intrabud signaling between receptor cell types, and secondly finally determining the identity of cells underlying amiloride-sensitive salt transduction.