An in vitro analysis of intestinal ammonia transport in fasted and fed freshwater rainbow trout: roles of NKCC, K+ channels, and Na+, K+ ATPase
An in vitro analysis of intestinal ammonia transport in fasted and fed freshwater rainbow trout: roles of NKCC, K+ channels, and Na+, K+ ATPase
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禁食和饲喂淡水虹鳟鱼肠道氨转运的体外分析：NKCC、K 通道和 Na、K ATP 酶的作用
DOI：
10.1007/s00360-019-01231-x
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
C. Wood
中科院分区：
文献类型：
--
作者：
J. Rubino;Jonathan M. Wilson;C. Wood
我们研究了未喂食和喂食的淡水虹鳟鱼（Oncorhynchus mykiss）前、中、后肠中氨处理的机制，重点研究了Na+:K+:2Cl−共转运体（NKCC）、Na+:K+ - atp酶（NKA）和K+通道。免疫组化发现NKCC位于肠细胞的粘膜（顶端）表面，饲喂后NKCC mRNA在肠细胞的前、后段表达上调。NH4+与K+在各肠段支持NKA活性的作用相同。采用体外肠囊制剂检测粘膜氨通量率（Jmamm，从粘膜盐水中消失）、浆膜氨通量率（Jsamm，在浆膜盐水中出现）和总组织氨生成率（Jtamm = Jsamm−Jmamm）。NKCC阻滞剂布美他尼（10−4 mol L−1）在大多数制剂中抑制Jsamm，但这主要是由于Jtamm的减少；Jmamm仅在饲喂动物的前肠中被显著抑制。在大多数制剂中，NKA阻滞剂瓦巴因（10−4 mol L−1）一般能降低Jmamm和Jsamm，但对Jtamm没有影响，尽管饲喂后前肠出现耐药性。钡（10−2 mol L−1）是一种K+通道阻滞剂，在大多数制剂中抑制Jmamm，在某些制剂中抑制Jsamm，但对Jtamm没有影响。这些药理学结果，以及对浆膜和粘膜Na+和K+浓度的反应表明，NKCC在氨吸收中的作用并不像以前认为的那么重要。NH4+似乎通过粘膜表面对钡敏感的K+通道被吸收。通过NKCC和K+通道的粘膜NH4+摄取是由基底侧NKA激活的，它在清除浆膜表面的NH4+方面起着额外的作用，可能会减少血液毒性或增强喂养后的离子摄取和氨基酸合成。结合其他研究的最新发现，我们提供了一个更新的模型来描述目前对硬骨鱼肠道氨运输的理解。
We examined mechanisms of ammonia handling in the anterior, mid, and posterior intestine of unfed and fed freshwater rainbow trout (Oncorhynchus mykiss), with a focus on the Na+:K+:2Cl− co-transporter (NKCC), Na+:K +-ATPase (NKA), and K+ channels. NKCC was localized by immunohistochemistry to the mucosal (apical) surface of enterocytes, and NKCC mRNA was upregulated after feeding in the anterior and posterior segments. NH4+ was equally potent to K+ in supporting NKA activity in all intestinal sections. In vitro gut sac preparations were employed to examine mucosal ammonia flux rates (Jmamm, disappearance from the mucosal saline), serosal ammonia flux rates (Jsamm, appearance in the serosal saline), and total tissue ammonia production rates (Jtamm = Jsamm − Jmamm). Bumetanide (10−4 mol L−1), a blocker of NKCC, inhibited Jsamm in most preparations, but this was largely due to reduction of Jtamm; Jmamm was significantly inhibited only in the anterior intestine of fed animals. Ouabain (10−4 mol L−1), a blocker of NKA, generally reduced both Jmamm and Jsamm without effects on Jtamm in most preparations, though the anterior intestine was resistant after feeding. Barium (10−2 mol L−1), a blocker of K+ channels, inhibited Jmamm in most preparations, and Jsamm in some, without effects on Jtamm. These pharmacological results, together with responses to manipulations of serosal and mucosal Na+ and K+ concentrations, suggest that NKCC is not as important in ammonia absorption as previously believed. NH4+ appears to be taken up through barium-sensitive K+ channels on the mucosal surface. Mucosal NH4+ uptake via both NKCC and K+ channels is energized by basolateral NKA, which plays an additional role in scavenging NH4+ on the serosal surface to possibly minimize blood toxicity or enhance ion uptake and amino acid synthesis following feeding. Together with recent findings from other studies, we have provided an updated model to describe the current understanding of intestinal ammonia transport in teleost fish.
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