Role of the ectonucleotidase NTPDase2 in taste bud function
Role of the ectonucleotidase NTPDase2 in taste bud function
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DOI：
10.1073/pnas.1309468110
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发表时间：
2013-09-03
影响因子：
11.1
通讯作者：
Kinnamon, Sue C.
中科院分区：
文献类型：
--
作者：
Vandenbeuch, Aurelie;Anderson, Catherine B.;Kinnamon, Sue C.
味蕾是不寻常的，它需要ATP作为传递器来激活感觉神经纤维。味觉细胞在味觉刺激下释放ATP，激活味觉神经上含有P2X2和P2X3亚基的嘌呤能受体。随后，释放的ATP被质膜核苷三磷酸水解为ADP，之前被鉴定为核苷三磷酸二磷酸水解酶-2 （NTPDase2）。在本文中，我们研究了这种外核苷酸酶在味蕾功能中的作用，通过检测基因靶向的缺乏NTPDase2的小鼠。RT-PCR证实了NTPDase2的缺失，并且atp酶组织化学显示敲除小鼠味蕾中没有反应产物，提示NTPDase2是味蕾中的主要形式。RT-PCR和免疫细胞化学表明，在基因敲除小鼠的味蕾中存在所有类型的细胞，即使是那些正常表达NTPDase2的细胞。此外，entpd2缺失小鼠味蕾的总体数量和大小均正常。敲除小鼠环瓣组织的荧光素/荧光素酶测定检测到细胞外ATP水平升高。来自鼓室索和舌咽部两条味觉神经的电生理记录显示，在entpd2缺失的小鼠中，对所有味觉刺激的反应都受到抑制。舌咽神经的反应比鼓室索神经更低，并涉及所有味觉品质；鼓室索对甜味和鲜味刺激的反应比对其他品质刺激的反应更压抑。我们认为，在entpd2基因敲除的动物中，细胞外ATP水平过高会使与神经纤维相关的P2X受体脱敏，从而抑制味觉反应。
Taste buds are unusual in requiring ATP as a transmitter to activate sensory nerve fibers. In response to taste stimuli, taste cells release ATP, activating purinergic receptors containing the P2X2 and P2X3 subunits on taste nerves. In turn, the released ATP is hydrolyzed to ADP by a plasma membrane nucleoside triphosphate previously identified as nucleoside triphosphate diphosphohydrolase-2 (NTPDase2). In this paper we investigate the role of this ectonucleotidase in the function of taste buds by examining gene-targeted Entpd2-null mice globally lacking NTPDase2. RT-PCR confirmed the absence of NTPDase2, and ATPase enzyme histochemistry reveals no reaction product in taste buds of knockout mice, suggesting that NTPDase2 is the dominant form in taste buds. RT-PCR and immunocytochemistry demonstrated that in knockout mice all cell types are present in taste buds, even those cells normally expressing NTPDase2. In addition, the overall number and size of taste buds are normal in Entpd2-null mice. Luciferin/luciferase assays of circumvallate tissue of knockout mice detected elevated levels of extracellular ATP. Electrophysiological recordings from two taste nerves, the chorda tympani and glossopharyngeal, revealed depressed responses to all taste stimuli in Entpd2-null mice. Responses were more depressed in the glossopharyngeal nerve than in the chorda tympani nerve and involved all taste qualities; responses in the chorda tympani were more depressed to sweet and umami stimuli than to other qualities. We suggest that the excessive levels of extracellular ATP in the Entpd2-knockout animals desensitize the P2X receptors associated with nerve fibers, thereby depressing taste responses.