Department of Otolaryngology, University of Colorado, Denver, CO, USA.
BMC Neurosci. 2010 Jun 21;11:77. doi: 10.1186/1471-2202-11-77.
Glutamate has been proposed as a transmitter in the peripheral taste system in addition to its well-documented role as an umami taste stimulus. Evidence for a role as a transmitter includes the presence of ionotropic glutamate receptors in nerve fibers and taste cells, as well as the expression of the glutamate transporter GLAST in Type I taste cells. However, the source and targets of glutamate in lingual tissue are unclear. In the present study, we used molecular, physiological and immunohistochemical methods to investigate the origin of glutamate as well as the targeted receptors in taste buds.
Using molecular and immunohistochemical techniques, we show that the vesicular transporters for glutamate, VGLUT 1 and 2, but not VGLUT3, are expressed in the nerve fibers surrounding taste buds but likely not in taste cells themselves. Further, we show that P2X2, a specific marker for gustatory but not trigeminal fibers, co-localizes with VGLUT2, suggesting the VGLUT-expressing nerve fibers are of gustatory origin. Calcium imaging indicates that GAD67-GFP Type III taste cells, but not T1R3-GFP Type II cells, respond to glutamate at concentrations expected for a glutamate transmitter, and further, that these responses are partially blocked by NBQX, a specific AMPA/Kainate receptor antagonist. RT-PCR and immunohistochemistry confirm the presence of the Kainate receptor GluR7 in Type III taste cells, suggesting it may be a target of glutamate released from gustatory nerve fibers.
Taken together, the results suggest that glutamate may be released from gustatory nerve fibers using a vesicular mechanism to modulate Type III taste cells via GluR7.
谷氨酸除了作为鲜味味觉刺激物的作用外,还被提出作为外周味觉系统的递质。作为递质的证据包括神经纤维和味觉细胞中存在离子型谷氨酸受体,以及在 I 型味觉细胞中表达谷氨酸转运体 GLAST。然而,舌组织中谷氨酸的来源和靶标尚不清楚。在本研究中,我们使用分子、生理和免疫组织化学方法来研究味觉感受器中谷氨酸的起源以及靶向受体。
我们使用分子和免疫组织化学技术表明,囊泡谷氨酸转运体 VGLUT1 和 2 表达在包围味蕾的神经纤维中,但可能不在味觉细胞本身中。此外,我们表明 P2X2,一种用于味觉而不是三叉神经纤维的特定标记物,与 VGLUT2 共定位,表明表达 VGLUT 的神经纤维来自味觉。钙成像表明,GAD67-GFP 型 III 味觉细胞而不是 T1R3-GFP 型 II 细胞对谷氨酸浓度做出反应,这些反应部分被 NBQX 阻断,NBQX 是一种特定的 AMPA/ kainate 受体拮抗剂。RT-PCR 和免疫组织化学证实了 Kainate 受体 GluR7 存在于 III 型味觉细胞中,表明其可能是来自味觉神经纤维释放的谷氨酸的靶标。
综上所述,结果表明,谷氨酸可能通过囊泡机制从味觉神经纤维释放出来,通过 GluR7 调节 III 型味觉细胞。