Mouse taste cells with G protein-coupled taste receptors lack voltage-gated calcium channels and SNAP-25
Mouse taste cells with G protein-coupled taste receptors lack voltage-gated calcium channels and SNAP-25
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DOI：
10.1186/1741-7007-4-7
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发表时间：
2006-03-30
期刊：
影响因子：
5.4
通讯作者：
Kinnamon, SC
中科院分区：
文献类型：
--
作者：
Clapp, TR;Medler, KF;Kinnamon, SC
背景：味觉感受器细胞负责传递来自环境的化学刺激，并将信息传递到神经系统。苦味、甜味和鲜味刺激利用G蛋白偶联受体激活II型味觉细胞中的磷脂酶C(PLC)信号通路。然而，目前还不知道这些细胞是如何与神经系统沟通的。先前的研究表明，表达T2R苦味受体的味觉细胞亚群缺乏电压门控钙通道，这通常是传统突触进行突触传递所必需的。在这里，我们使用两个表达来自两个味觉特异性启动子的绿色荧光蛋白(GFP)的转基因小鼠来检测II型细胞亚群中的钙信号：T1R3-GFP小鼠用于鉴定甜味和鲜味敏感的味觉细胞，而Trpm5-GFP小鼠用于鉴定所有利用PLC信号通路进行转导的细胞。用钙离子成像和全细胞记录评估电压门控性钙电流，免疫细胞化学检测味觉细胞中与常规突触相关的突触前SNAP-25蛋白的表达。结果：高K+去极化导致两种转基因小鼠的一小部分非GFP标记细胞内钙离子浓度增加。相反，在表达GFP的味觉细胞中，没有观察到去极化引起的钙反应，但GFP标记的细胞对PLC激活剂m-3M3FBS有反应，表明这些细胞是活的。全细胞记录显示，两种基因型的GFP标记细胞都有较小的电压依赖性Na+和K+电流，但没有钙电流的证据。一组非GFP标记的味觉细胞显示出大的电压依赖性的Na+和K+电流以及高阈值电压门控的钙电流。免疫细胞化学显示SNAP-25在不同的味觉细胞中表达，而不是表达T1R3或Trpm5的味觉细胞。这些数据表明G蛋白偶联的味觉受体和传统的突触信号机制在不同的味觉细胞中表达。结论：负责传递苦味、甜味和鲜味刺激的味觉受体细胞不太可能通过传统的化学突触与神经纤维进行交流。
Background: Taste receptor cells are responsible for transducing chemical stimuli from the environment and relaying information to the nervous system. Bitter, sweet and umami stimuli utilize G-protein coupled receptors which activate the phospholipase C ( PLC) signaling pathway in Type II taste cells. However, it is not known how these cells communicate with the nervous system. Previous studies have shown that the subset of taste cells that expresses the T2R bitter receptors lack voltage-gated Ca2+ channels, which are normally required for synaptic transmission at conventional synapses. Here we use two lines of transgenic mice expressing green fluorescent protein ( GFP) from two taste-specific promoters to examine Ca2+ signaling in subsets of Type II cells: T1R3-GFP mice were used to identify sweet- and umami-sensitive taste cells, while TRPM5-GFP mice were used to identify all cells that utilize the PLC signaling pathway for transduction. Voltage-gated Ca2+ currents were assessed with Ca2+ imaging and whole cell recording, while immunocytochemistry was used to detect expression of SNAP-25, a presynaptic SNARE protein that is associated with conventional synapses in taste cells.Results: Depolarization with high K+ resulted in an increase in intracellular Ca2+ in a small subset of non-GFP labeled cells of both transgenic mouse lines. In contrast, no depolarization-evoked Ca2+ responses were observed in GFP-expressing taste cells of either genotype, but GFP-labeled cells responded to the PLC activator m-3M3FBS, suggesting that these cells were viable. Whole cell recording indicated that the GFP-labeled cells of both genotypes had small voltage-dependent Na+ and K+ currents, but no evidence of Ca2+ currents. A subset of non-GFP labeled taste cells exhibited large voltage-dependent Na+ and K+ currents and a high threshold voltage-gated Ca2+ current. Immunocytochemistry indicated that SNAP-25 was expressed in a separate population of taste cells from those expressing T1R3 or TRPM5. These data indicate that G protein-coupled taste receptors and conventional synaptic signaling mechanisms are expressed in separate populations of taste cells.Conclusion: The taste receptor cells responsible for the transduction of bitter, sweet, and umami stimuli are unlikely to communicate with nerve fibers by using conventional chemical synapses.