PHYSIOLOGY OF GLUTAMATE RECEPTORS IN TASTE BUDS

氨基酸L-谷氨酸在人体内能引起一种独特的味觉，这种感觉被称为“鲜味”。鲜味感觉的一个重要特征是，5‘-GMP和5’-IMP等5‘核苷酸的存在会增强这种感觉。参与谷氨酸味道的受体及其被核苷酸调控的机制目前尚不清楚，尽管我们在之前的资金支持期间获得了证据，表明其中一种受体是代谢性谷氨酸受体mGluR4的味道特异性形式。在接下来的资助期间，我们将研究mGluR4和其他谷氨酸受体在谷氨酸的味觉转导中的作用。具体目的如下：(1)确定味蕾中谷氨酸受体的分布。对谷氨酸的反应可能涉及激活基底外侧神经递质受体和顶端味觉受体。我们将利用一种方法，允许刺激在整个细胞记录期间独立地施加到味蕾的顶端和基侧膜上，以确定谷氨酸受体的细胞分布。(2)探讨谷氨酸作为味觉刺激物的转导及5‘-核苷酸对其调节的生理机制。我们将利用全细胞和单通道膜片钳记录和单个味觉细胞的钙成像来确定参与谷氨酸味觉转导的第二信使和离子通道。(3)确定Gustducin是否参与谷氨酸转导。Gustducin是一种味觉特异的G蛋白，在味觉细胞亚群中表达。我们将使用转基因小鼠，在其中表达味觉蛋白的味觉细胞也表达绿色荧光蛋白，这样它们就可以被识别并记录下来。我们也有Gustducin缺失的小鼠，其中Gustducin基因已经被删除。我们将比较Gustducin表达的小鼠和Gustducin缺失的小鼠对谷氨酸激动剂的反应，以确定Gustducin是否在谷氨酸转导中发挥作用。

The amino acid L-glutamate elicits a unique taste sensation in humans that has been termed "umami". An important feature of the umami sensation is that it is potentiated by the presence of 5' ribonucleotides such as 5'-GMP and 5'-IMP. The receptors involved in glutamate taste and the mechanisms involved in their modulation by nucleotides are definitively not known, although we have obtained evidence during the previous funding period that one of the receptors involved is a taste- specific form of the metabotropic glutamate receptor mGluR4. During the next funding period we will investigate the role of mGluR4 and other glutamate receptors in the taste transduction of glutamate. The specific aims are as follows: (1) To determine the distribution of glutamate receptors in taste buds. It is possible that responses to glutamate involve activation of basolateral neurotransmitter receptors as well as apical taste receptors. We will utilize an approach that allow stimuli to be applied independently to apical and basolateral membranes of taste buds during whole cell recording to determine the cellular distribution of glutamate receptors. (2) To determine the physiological mechanisms involved in the transduction of glutamate as a taste stimulus and its modulation by 5'- ribonucleotides. We will utilize whole-cell and single-channel patch- clamp records and Ca2+ imaging of single taste cells to determine the second messengers and ion channels involved in glutamate taste transduction. (3) To determine is gustducin is involved in the transduction of glutamate. Gustducin is a taste-specific G protein that is expressed in subset of taste cells. We will use transgenic mice in which the gustducin-expressing taste cells also express green fluorescent protein, so that they can be identified for record. We also have gustducin-null mice, in which the gustducin gene has been deleted. We will compare responses to glutamate agonists in gustducin-expressing and gustducin-null mice to determine if gustducin plays a role in glutamate transduction.