Evidence for the functional involvement of members of the TRP channel family in the uptake of Na+ and NH4+ by the ruminal epithelium
Evidence for the functional involvement of members of the TRP channel family in the uptake of Na+ and NH4+ by the ruminal epithelium
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DOI：
10.1007/s00424-016-1835-4
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
J. Rosendahl;H. Braun;K. T. Schrapers;Holger Martens;F. Stumpff
中科院分区：
文献类型：
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作者：
J. Rosendahl;H. Braun;K. T. Schrapers;Holger Martens;F. Stumpff
大量蛋白质在肠道的发酵部分被降解为氨，氨被吸收、解毒为尿素并排出体外，从而形成氮化合物，如与全球变暖有关的一氧化二氮。在反刍动物中，通道介导的NH4+从瘤胃吸收占主导地位。这些通道的分子特性仍有待澄清。采用膜片钳、ususing chamber、微电极技术和qPCR对牛和羊的瘤胃细胞和上皮进行了研究。在膜片钳实验中，牛瘤胃上皮细胞表达了一种对NH4+的电导，这种电导可以通过电压依赖的方式被二价阳离子阻断。在天然上皮中，NH4+使顶端电位去极化，使细胞质酸化，并诱导在去除Na+后持续存在的短路电流（Isc）上升，维拉帕米可阻断该电流，去除二价阳离子可增强该电流，并且对某些瞬时受体电位（TRP）通道调节剂敏感。薄荷醇或百里香酚以剂量依赖性的方式刺激含有Na+或NH4+的iscin溶液，并调节经上皮Ca2+通量。在信使RNA （mRNA）水平上，绵羊和牛瘤胃上皮表达TRPA1、TRPV3、TRPV4、TRPM6和TRPM7， TRPV6的表达处于边缘。未检测到TRPV1、TRPV5或TRPM8的条带。功能和分子生物学数据表明，NH4+、Na+和Ca2+在瘤胃中的转运涉及TRP通道，其中TRPV3和TRPA1是主要的候选基因。TRP通道也可能参与NH4+在其他上皮细胞间的转运。
Large quantities of protein are degraded in the fermentative parts of the gut to ammonia, which is absorbed, detoxified to urea, and excreted, leading to formation of nitrogenous compounds such as N2O that are associated with global warming. In ruminants, channel-mediated uptake of NH4+from the rumen predominates. The molecular identity of these channels remains to be clarified. Ruminal cells and epithelia from cows and sheep were investigated using patch clamp, Ussing chamber, microelectrode techniques, and qPCR. In patch clamp experiments, bovine ruminal epithelial cells expressed a conductance for NH4+that could be blocked in a voltage-dependent manner by divalent cations. In the native epithelium, NH4+depolarized the apical potential, acidified the cytosol and induced a rise in short-circuit current (Isc) that persisted after the removal of Na+, was blocked by verapamil, enhanced by the removal of divalent cations, and was sensitive to certain transient receptor potential (TRP) channel modulators. Menthol or thymol stimulated theIscin Na+or NH4+containing solutions in a dose-dependent manner and modulated transepithelial Ca2+fluxes. On the level of messenger RNA (mRNA), ovine and bovine ruminal epithelium expressed TRPA1, TRPV3, TRPV4, TRPM6, and TRPM7, with any expression of TRPV6 marginal. No bands were detected for TRPV1, TRPV5, or TRPM8. Functional and molecular biological data suggest that the transport of NH4+, Na+, and Ca2+across the rumen involves TRP channels, with TRPV3 and TRPA1 emerging as prime candidate genes. TRP channels may also contribute to the transport of NH4+across other epithelia.