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

第二信使系统参与了鲜味、苦味和甜味的传递。利用电生理技术，分析了小鼠味觉细胞中苦味和鲜味的转导机制。鲜味具有味精与核苷酸协同作用等独特的特点。我们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蛋白参与鲜味转导的膜片钳记录。已经确定了两个假定的谷氨酸G蛋白偶联受体，taste-mGluR4和氨基酸受体T1R1/T1R3异源二聚体。但是，精确的转导机制仍然未知。通过神经记录，我们测量了小鼠对味精、IMP以及味精和IMP混合物的反应。舌咽神经对各氨基酸和IMP均有轻微反应。当氨基酸- imp混合溶液刺激时，反应是相加的，而不是协同的。氨基酸溶液对脊索鼓室神经的反应较大。与舌咽神经相比，味精和L-AspNa在鼓室神经的反应明显增强。此外，当添加IMP时，L-AspNa表现出协同效应。这些结果表明，T1R1/T1R3接收氨基酸，参与了鲜味的协同作用。地那铵苦味的转导可能涉及cAMP和IP_3。记录了GDP-βs m磷脂酶C抑制剂或8-Br-cAMP对地那铵反应的影响，发现还有另一条与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美味的，而毒素和药物中的苦味物质则令人难以下咽。我们还通过膜片钳和双瓶偏好测试，提出了可接受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.