Schneebauer Gabriel, Drechsel Victoria, Dirks Ron, Faserl Klaus, Sarg Bettina, Pelster Bernd
Institute of Zoology, University of Innsbruck, Innsbruck, Austria.
Center for Molecular Biosciences, University Innsbruck, Innsbruck, Austria.
BMC Genomics. 2021 Dec 2;22(1):866. doi: 10.1186/s12864-021-08180-2.
In physoclist fishes filling of the swimbladder requires acid secretion of gas gland cells to switch on the Root effect and subsequent countercurrent concentration of the initial gas partial pressure increase by back-diffusion of gas molecules in the rete mirabile. It is generally assumed that the rete mirabile functions as a passive exchanger, but a detailed analysis of lactate and water movements in the rete mirabile of the eel revealed that lactate is diffusing back in the rete. In the present study we therefore test the hypothesis that expression of transport proteins in rete capillaries allows for back-diffusion of ions and metabolites, which would support the countercurrent concentrating capacity of the rete mirabile. It is also assumed that in silver eels, the migratory stage of the eel, the expression of transport proteins would be enhanced.
Analysis of the transcriptome and of the proteome of rete mirabile tissue of the European eel revealed the expression of a large number of membrane ion and metabolite transport proteins, including monocarboxylate and glucose transport proteins. In addition, ion channel proteins, Ca-ATPase, Na/K-ATPase and also FF-ATP synthase were detected. In contrast to our expectation in silver eels the expression of these transport proteins was not elevated as compared to yellow eels. A remarkable number of enzymes degrading reactive oxygen species (ROS) was detected in rete capillaries.
Our results reveal the expression of a large number of transport proteins in rete capillaries, so that the back diffusion of ions and metabolites, in particular lactate, may significantly enhance the countercurrent concentrating ability of the rete. Metabolic pathways allowing for aerobic generation of ATP supporting secondary active transport mechanisms are established. Rete tissue appears to be equipped with a high ROS defense capacity, preventing damage of the tissue due to the high oxygen partial pressures generated in the countercurrent system.
在闭鳔鱼类中，鱼鳔充气需要气腺细胞分泌酸来开启鲁特效应，随后通过气体分子在奇网中的逆向扩散，使初始气体分压增加并进行逆流浓缩。一般认为奇网起到被动交换器的作用，但对鳗鱼奇网中乳酸和水流动的详细分析表明，乳酸在奇网中逆向扩散。因此，在本研究中，我们检验了以下假设：奇网毛细血管中转运蛋白的表达允许离子和代谢物的逆向扩散，这将支持奇网的逆流浓缩能力。还假设在银鳗（鳗鱼的洄游阶段）中，转运蛋白的表达会增强。
对欧洲鳗鱼奇网组织的转录组和蛋白质组分析显示，大量膜离子和代谢物转运蛋白表达，包括单羧酸和葡萄糖转运蛋白。此外，还检测到离子通道蛋白、钙 - ATP酶、钠/钾 - ATP酶以及F0F1 - ATP合酶。与我们的预期相反，银鳗中这些转运蛋白的表达与黄鳗相比并未升高。在奇网毛细血管中检测到大量降解活性氧（ROS）的酶。
我们的结果揭示了奇网毛细血管中大量转运蛋白的表达，因此离子和代谢物，特别是乳酸的逆向扩散可能会显著增强奇网的逆流浓缩能力。建立了支持次级主动转运机制的需氧产生ATP的代谢途径。奇网组织似乎具备较高的ROS防御能力，可防止因逆流系统中产生的高氧分压对组织造成损伤。
