MOLECULAR PHYSIOLOGY OF GLUTAMATE IN TASTE

L-谷氨酸，以其一钠盐(MSG)的形式，是一种独特而有效的味觉刺激，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在味觉受体细胞中是否发现了类似于大脑突触的谷氨酸受体(GluR)，并可能传递味精的味道。这一目标是通过分子生物学(项目#1，细胞生物代谢和一个或多个离子型GluR在大鼠味蕾细胞中表达)来实现的。这些受体类似于CNS GluRs，但具有重要的序列和功能差异，可能意味着在味觉转导中发挥作用。最后，我们获得了一种新的味觉特异性代谢性谷氨酸受体(味觉-mGluR4)在味精味觉转导中所起作用的关键分子和功能证据。在下一阶段，我们建议进行更严格的测试，以区分味觉-mGluR4对于味觉转导是否必要和充分，或者是否也可能涉及额外的GluRs。这个问题将通过对味蕾细胞和从味蕾中克隆的GluRs转基因异源细胞的分子和功能分析来解决。我们将获得克隆受体的详细药理学特征(项目1)，并将这些数据与作为味觉刺激剂的药物在分离组织(项目3)和完整舌体(项目2)中的反应进行比较。功能研究将包括第二信使的生化测量(项目1)、味觉感受器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觉刺激味精S的转导。这个项目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.