Department of Zoology, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4
Department of Zoology, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
J Exp Biol. 2020 Jul 13;223(Pt 13):jeb216309. doi: 10.1242/jeb.216309.
The osmorespiratory compromise is a physiological trade-off between the characteristics of the gill that promote respiratory gas exchange and those that limit passive flux of ions and water with the environment. In hypoxia, changes in gill blood flow patterns and functional surface area that increase gas transfer can promote an exacerbation in ion and water flux. Our goal was to determine whether the osmorespiratory compromise is flexible, depending on environmental salinity (fresh, isosmotic and sea water) and oxygen levels (hypoxia) in euryhaline killifish, Plasma ion concentrations were minimally affected by hypoxia, indicating a maintenance of osmoregulatory homeostasis. In freshwater killifish, hypoxia exposure reduced branchial Na/K-ATPase and NEM-sensitive ATPase activities, as well as diffusive water flux rates. Unidirectional Na influx and Na efflux decreased during hypoxia in freshwater, but net Na flux remained unchanged. Net loss rates of Cl, K and ammonia were also attenuated in hypoxia, suggesting both transcellular and paracellular reductions in permeability. These reductions appeared to be regulated phenomena as fluxes were restored immediately in normoxia. Na flux rates increased during hypoxia in 11 ppt, but decreased in 35 ppt, the latter suggesting a similar response to hypoxia to that in freshwater. In summary, freshwater and seawater killifish experience a reduction in gill permeability, as seen in other hypoxia-tolerant species. Fish acclimated to isosmotic salinity increased Na influx and efflux rates, as well as paracellular permeability in hypoxia, responses in accord with the predictions of the classic osmorespiratory compromise.
渗透呼吸权衡是一种生理上的权衡，涉及促进呼吸气体交换的鳃的特性和限制离子和水与环境被动通量的鳃的特性。在低氧条件下，增加气体交换的鳃血流模式和功能表面积的变化会促进离子和水通量的加剧。我们的目标是确定渗透呼吸权衡是否具有灵活性，这取决于广盐性（淡水、等渗和海水）和氧气水平（低氧）对弹涂鱼的影响。血浆离子浓度受低氧影响最小，表明渗透调节的稳态得到维持。在淡水中，低氧暴露降低了鳃 Na/K-ATP 酶和 NEM 敏感 ATP 酶的活性以及扩散水通量速率。在淡水低氧期间，单向 Na 内流和 Na 外流减少，但净 Na 通量保持不变。Cl、K 和氨的净损失率在低氧条件下也降低，表明跨细胞和旁细胞通透性降低。这些减少似乎是调节现象，因为在正常氧条件下通量立即恢复。在 11 ppt 中，低氧期间 Na 通量增加，但在 35 ppt 中减少，后者表明对低氧的反应类似于淡水。总之，淡水和海水弹涂鱼经历了鳃通透性的降低，这在其他耐低氧物种中也有观察到。适应等渗盐度的鱼类在低氧条件下增加了 Na 内流和外流速率以及旁细胞通透性，这与经典渗透呼吸权衡的预测一致。
