Robertson Lisa M, Wood Chris M
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada.
J Exp Biol. 2014 May 1;217(Pt 9):1425-9. doi: 10.1242/jeb.099879. Epub 2014 Jan 16.
The influence of swimming activity on gill paracellular permeability has not been measured previously in fishes. We critically assessed the use of tritium-labeled polyethylene glycol ([(3)H]PEG-4000) for this purpose, a substance that is also a classic marker for extracellular fluid volume, glomerular filtration rate and drinking rate. Tests (8 h) on resting freshwater trout showed that when measuring [(3)H]PEG-4000 clearance from the plasma in the efflux direction, correction for a large excretion via glomerular filtration was essential, necessitating urinary catheterization. When measuring [(3)H]PEG-4000 clearance from the water in the influx direction, correction for a significant uptake by drinking was essential, necessitating terminal gut removal, whereas glomerular filtration losses were minimal. After correction for these alternate routes of loss and uptake, [(3)H]PEG-4000 clearance rates by efflux from the plasma and by influx from the water were identical, showing that gill paracellular permeability is not rectified, and can be measured in either direction. The influx technique with terminal gut removal was used to assess gill paracellular permeability in trout without urinary catheters freely swimming at 1.2 body lengths s(-1) for 8 h. Branchial [(3)H]PEG-4000 clearance rate (by influx from the water) increased significantly by ~80% in accord with a similar measured increase in O2 consumption rate. Thus in trout, gill paracellular permeability does increase during exercise, in accord with the traditional concept of the osmorespiratory compromise.
游泳活动对鱼类鳃旁细胞通透性的影响此前尚未测定。我们严格评估了为此目的使用氚标记的聚乙二醇（[(3)H]PEG - 4000），该物质也是细胞外液体积、肾小球滤过率和饮水率的经典标志物。对静息淡水鳟鱼进行的8小时测试表明，在测量[(3)H]PEG - 4000从血浆中向外流出方向的清除率时，必须对通过肾小球滤过的大量排泄进行校正，这需要进行尿道插管。在测量[(3)H]PEG - 4000从水中向内流入方向的清除率时，必须对因饮水导致的显著摄取进行校正，这需要在实验结束时切除肠道，而肾小球滤过损失最小。在对这些替代的损失和摄取途径进行校正后，[(3)H]PEG - 4000从血浆中向外流出和从水中向内流入的清除率相同，表明鳃旁细胞通透性没有整流现象，并且可以在任一方向进行测量。采用在实验结束时切除肠道的向内流入技术，对未进行尿道插管、以1.2体长每秒（s(-1)）的速度自由游泳8小时的鳟鱼的鳃旁细胞通透性进行评估。鳃部[(3)H]PEG - 4000清除率（通过从水中向内流入）显著增加了约80%，这与测得的耗氧率的类似增加一致。因此，在鳟鱼中，鳃旁细胞通透性在运动过程中确实会增加，这与渗透压呼吸权衡的传统概念一致。
