Chaudhari N, Roper S D
Department of Physiology and Biophysics, University of Miami School of Medicine, Florida 33101, USA.
Ann N Y Acad Sci. 1998 Nov 30;855:398-406. doi: 10.1111/j.1749-6632.1998.tb10598.x.
Recent molecular analyses have demonstrated that a metabotropic glutamate receptor, mGluR4, is expressed in taste buds from rat circumvallate and foliate papillae. Behavioral studies demonstrated that L(+)-2-amino-4-phosphonobutyric acid (L-AP4), an agonist for mGluR4 and related receptors, mimics the taste of monosodium glutamate (MSG) in rats. mGluR4 is known to signal through inhibition of the cyclic adenosine-5',3'-monophosphate (cAMP) cascade. Circumvallate and foliate taste buds exhibit decreases of cAMP levels following stimulation with MSG, and the response is potentiated by 5'-inosine monophosphate, suggesting that it is related to umami taste. Further, experiments on mice with the mGluR4 gene knocked out support the interpretation that mGluR4 is a key component in glutamate taste. Glutamate may also stimulate taste buds through an ionotropic receptor pathway. In patch-clamp studies, glutamate evokes two types of currents, similar to those elicited by N-methyl-D-aspartate (NMDA) and L-AP4. We speculate upon the significance of two glutamate receptor pathways in taste buds.
最近的分子分析表明，一种代谢型谷氨酸受体mGluR4在大鼠轮廓乳头和叶状乳头的味蕾中表达。行为学研究表明，L(+)-2-氨基-4-磷酸丁酸（L-AP4），一种mGluR4及相关受体的激动剂，在大鼠中能模拟味精（MSG）的味道。已知mGluR4通过抑制环磷酸腺苷（cAMP）级联反应来传递信号。轮廓乳头和叶状味蕾在受到味精刺激后会出现cAMP水平下降，并且5'-肌苷单磷酸会增强这种反应，这表明它与鲜味味觉有关。此外，对敲除mGluR4基因的小鼠进行的实验支持了mGluR4是谷氨酸味觉关键成分的解释。谷氨酸也可能通过离子型受体途径刺激味蕾。在膜片钳研究中，谷氨酸会引发两种类型的电流，类似于由N-甲基-D-天冬氨酸（NMDA）和L-AP4引发的电流。我们推测了味蕾中两种谷氨酸受体途径的意义。
