Study on Cross-talk of second messenger system in taste transduction

已有研究表明，第二信使系统参与了鲜味、苦味和甜味的信号转导，本文采用电生理技术分析了小鼠味觉细胞中苦味和鲜味信号转导的机制，发现鲜味具有独特的特征，如味精与核苷酸的协同作用。我们用膜片钳技术记录了单个味觉细胞对谷氨酸激动剂-IMP混合物的协同反应，并报道了G蛋白参与鲜味信号转导。已经鉴定了两种推定的谷氨酸G蛋白偶联受体，味觉-mGluR4和氨基酸受体T1R1/T1R3异二聚体。但是，精确的转导机制仍然是未知的。采用神经记录技术，测定了小鼠轮状核和叶状核对味精（MSG）、IMP以及味精和IMP混合物的反应。舌咽神经对每种氨基酸和IMP反应轻微。当用氨基酸-IMP混合溶液刺激时，反应是相加的而不是协同的。氨基酸溶液在鼓索神经引起较大的反应。与舌咽神经相比，MSG和L-AspNa在鼓索神经的反应性显著增强。此外，当加入IMP时，L-AspNa显示出协同效应。这些结果表明，T1R1/T1R3接受氨基酸，参与了鲜味的协同效应，地那铵苦味的传递可能与cAMP和IP_3有关。记录GDP-β s m抑制剂磷脂酶C或8-Br-cAMP对地那铵反应的影响，发现存在另一条与G蛋白无关的途径。此外，该途径是通过细胞内Ca ^<2 +>的释放。食物中的苦味对人来说是可口的，而毒素和药物中的苦味物质则是不可口的。我们还利用膜片钳技术和两瓶偏好实验，提出了可接受苦味和不可接受苦味之间存在不同的机制。

It has been suggested that second messenger system are involved in umami, bitter and sweet taste transduction.Employing electrophysiological technique, I analyzed has bitter and umami transduction mechanism in mouse taste cells.Umami taste has unique feature such as synergism between MSG and nucleotide. We have recorded the synergistic responses in the single taste cells to glutamate agonists-IMP mixture and reported that G protein is involved in umami transduction using the patch-clamp recording. Two putative G protein coupled receptors for glutamate have been identified, taste-mGluR4 and the amino acid receptor T1R1/T1R3 heterodimer. But, precise transduction mechanisms are still unknown. Using nerve recording, we measured response to MSG, IMP and a mixture of MSG and IMP in mouse circumvallate and foliate. The glossopharyngeal nerve responded to each amino acid and IMP slightly. When it was stimulated with the amino acid-IMP mixture solutions, the responses were was additive rather than the synergistic. The amino acid solution induced larger response in chords tympani nerve. Compared with the glossopharyngeal nerve, the response of MSG and L-AspNa increased notably in the chords tympani nerve. Furthermore, when IMP was added, L-AspNa shown the synergistic effect. These results suggest that T1R1/T1R3 received amino acid and contributed to the synergistic effect of umami taste.Transduction of bitter taste of denatonium was suggested to involve cAMP and IP_3. Recording of effect of GDP-βs m inhibitor of phospholipase C or 8-Br-cAMP on denatonium response revealed that there is another pathway which is not related with G protein. Furthermore, the pathway is via release of intracellular Ca^<2+>. Bitterness from food is palatable for human, although bitter substances from toxins and medicines are unpalatable. We also suggested that there is different mechanisms between acceptable and non-acceptable bitterness using patch-clamp and two bottle preference test.