1 Department of Zoology, The University of British Columbia , Vancouver, British Columbia, Canada V6T 1Z4.
2 Department of Ocean Sciences, Memorial University of Newfoundland , St John's, Newfoundland, Canada A1C 5S7.
Proc Biol Sci. 2019 May 29;286(1903):20190339. doi: 10.1098/rspb.2019.0339.
A successful spawning migration in salmon depends on their athletic ability, and thus on efficient cardiovascular oxygen (O) transport. Most teleost fishes have highly pH-sensitive haemoglobins (Hb) that can release large amounts of O when the blood is acidified at the tissues. We hypothesized that plasma-accessible carbonic anhydrase (paCA; the enzyme that catalyses proton production from CO) is required to acidify the blood at the tissues and promote tissue O extraction. Previous studies have reported an elevated tissue O extraction in hypoxia-acclimated teleosts that may also be facilitated by paCA. Thus, to create experimental contrasts in tissue O extraction, Atlantic salmon were acclimated to normoxia or hypoxia (40% air saturation for more than six weeks), and the role of paCA in enhancing tissue O extraction was tested by inhibiting paCA at rest and during submaximal exercise. Our results show that: (i) in both acclimation groups, the inhibition of paCA increased cardiac output by one-third, indicating a role of paCA in promoting tissue O extraction during exercise, recovery and at rest; (ii) the recruitment of paCA was plastic and increased following hypoxic acclimation; and (iii) maximal exercise performance in salmon, and thus a successful spawning migration, may not be possible without paCA.
三文鱼的繁殖洄游是否成功取决于它们的运动能力，而运动能力又取决于心血管系统高效地向组织供氧。大多数硬骨鱼类都具有高度依赖于 pH 值的血红蛋白（Hb），当血液在组织中酸化时，Hb 可以大量释放氧气。我们假设，血浆可接触的碳酸酐酶（paCA；可催化 CO 产生质子的酶）是在组织中酸化血液并促进组织氧摄取所必需的。先前的研究报告称，在低氧适应的硬骨鱼类中，组织氧摄取量增加，这也可能是由 paCA 促进的。因此，为了在组织氧摄取方面创造实验对比，我们将大西洋三文鱼适应于常氧或低氧（40%空气饱和度，适应时间超过六周），并通过在休息和次最大运动期间抑制 paCA 来测试 paCA 增强组织氧摄取的作用。我们的结果表明：（i）在两个适应组中，paCA 的抑制使心输出量增加了三分之一，这表明 paCA 在运动、恢复和休息期间促进了组织氧摄取；（ii）paCA 的募集是可塑的，并随着低氧适应而增加；（iii）如果没有 paCA，三文鱼的最大运动表现，即成功的繁殖洄游，可能是不可能的。
