MOLECULAR PHYSIOLOGY OF GLUTAMATE IN TASTE

L-谷氨酸以其盐（MSG）的形式存在，是一种独特而有效的味觉刺激物，天然存在于许多食物中。该计划项目的第一个资助期的目标是确定是否在味觉受体细胞中发现类似于大脑突触的谷氨酸受体（GluRs），并可能抑制味精的味道。使用分子生物学（项目#1，细胞生物学代谢型和一种或多种离子型GluR在大鼠味蕾细胞中表达）来接近该目标。这些受体类似于CNS GluRs，但具有重要的序列和功能差异，这可能意味着在味觉转导中的作用。最后，我们获得了关键的分子和功能的证据，一个新的味觉特异性代谢型谷氨酸受体（taste-mGluR 4）在转导味精的味道的作用。在接下来的时间里，我们提出了更严格的测试，以区分味觉mGluR 4是否是必要的和足够的味精味觉转导，或是否额外的GluRs也可能参与。这个问题将通过分子和功能分析的味蕾细胞和异源细胞转染GluRs从味蕾克隆。我们将获得克隆受体的详细药理学特征（项目#1），并将这些数据与分离组织（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）。从分子水平和细胞水平到动物行为的多学科研究将有助于阐明味精作为味觉刺激物的转导机制。本计划的长期目标是为一个重要的味觉刺激提供一个全面的味觉传导分析。

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.