MOLECULAR PHYSIOLOGY OF GLUTAMATE IN TASTE

l -谷氨酸，以其单钠盐（MSG）的形式，是一种独特而有效的味觉刺激，存在于许多食物中。本项目第一个资助期的目标是确定味精受体（GluRs）是否与大脑突触中的谷氨酸受体（GluRs）相似，并可能在味觉受体细胞中传递味精的味道。这一目标是通过分子生物学（项目1）来实现的，细胞生物学代谢和一种或多种嗜离子性GluRs在大鼠味蕾细胞中表达。这些受体与CNS GluRs相似，但具有重要的序列和功能差异，可能暗示在味觉转导中起作用。最后，我们获得了一种新的味觉特异性代谢型谷氨酸受体（taste- mglur4）在味精味觉转导中的作用的关键分子和功能证据。在接下来的一段时间里，我们将提出更严格的测试来区分taste- mglur4是否对味精的味觉传导是必要的和充分的，或者是否还可能涉及其他GluRs。这个问题将通过味蕾细胞的分子和功能分析以及从味蕾克隆的GluRs转染的异源细胞来解决。我们将获得克隆受体的详细药理学资料（项目1），并将这些数据与在分离组织（项目3）和完整舌头（项目2）中用作味觉刺激的药理学试剂的反应进行比较。功能研究将包括第二信使的生化测量（项目#1），味觉受体细胞的膜片钳和钙成像（项目#2），味觉传入纤维活动的电生理记录（项目#2）和动物行为测试（项目#2）。这种从分子和细胞水平到动物行为的多学科转换努力将有助于阐明味精作为味觉刺激的转导。该项目的长期目标是对一种重要的味觉刺激提供味觉转导的综合分析。

L-Glutamate, in the form of its monosodium salt (MSG), is a distinctive and potent taste stimulus found naturally in many foods. The goal of the first funding period for this Program Project was to determine if glutamate receptors (GluRs) resembling those at synapses in the brain are found in taste receptor cells and might transduce MSG taste. This goal was approached using molecular biological (Project #1, cell biological metabotropic and one or more ionotropic GluRs are expressed in rat taste bud cells. These receptors are similar to CNS GluRs but have important sequence and functional differences that may imply a role in taste transduction. Lastly, we obtained critical molecular and functional evidence for the role of a novel taste-specific metabotropic glutamate receptor (taste-mGluR4) in transducing the taste of MSG. In the next period, we propose more stringent tests to discriminate whether taste-mGluR4 is necessary and sufficient for MSG taste transduction, or whether additional GluRs might also be involved. This question will be addressed through molecular and functional analysis of taste bud cells and heterologous cells transfected with GluRs cloned from taste buds. We will obtain detailed pharmacological profiles of cloned receptors (Project #1) and compare these data with the responses to pharmacological agents used as taste stimulate in isolated tissues (Project #3) and intact tongues (Project #2). Functional studies will include biochemical measurements of second messengers (Project #1), patch- clamp and calcium imaging of taste receptor cells (Project #2), electrophysiological recordings of gustatory afferent fiber activity (Project #2), and animal behavioral tests (Project #2). This converted multi-disciplinary effort from molecular and cellular levels to animals behavior will serve to elucidate the transduction of MSG s a taste stimulus. The long term of this Program Project is to provide a comprehensive analysis of taste transduction for an important gustatory stimulus.