Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA.
J Exp Biol. 2024 Dec 1;227(23). doi: 10.1242/jeb.247916. Epub 2024 Nov 28.
Oxygen availability is central to the energetic budget of aquatic animals and may vary naturally and/or in response to anthropogenic activities. Yet, we know little about how oxygen availability is linked to fundamental processes such as ion transport in aquatic insects. We hypothesized and observed that ion (22Na and 35SO4) uptake would be significantly decreased at O2 partial pressures below the mean critical level (Pcrit, 5.4 kPa) where metabolic rate (ṀO2) is compromised and ATP production is limited. However, we were surprised to observe marked reductions in ion uptake at oxygen partial pressures well above Pcrit, where ṀO2 was stable. For example, SO4 uptake decreased by 51% at 11.7 kPa and 82% at Pcrit (5.4 kPa) while Na uptake decreased by 19% at 11.7 kPa and 60% at Pcrit. Nymphs held for longer time periods at reduced PO2 exhibited stronger reductions in ion uptake rates. Fluids from whole-body homogenates exhibited a 29% decrease in osmolality in the most hypoxic condition. The differential expression of atypical guanylate cyclase (gcy-88e) in response to changing PO2 conditions provides evidence for its potential role as an oxygen sensor. Several ion transport genes (e.g. chloride channel and sodium-potassium ATPase) and hypoxia-associated genes (e.g. ldh and egl-9) were also impacted by decreased oxygen availability. Together, the results of our work suggest that N. triangulifer can sense decreased oxygen availability and perhaps conserves energy accordingly, even when ṀO2 is not impacted.
氧气供应是水生动物能量预算的核心，其会自然变化和/或响应人为活动而变化。然而，我们对于氧气供应如何与基本过程（如水生昆虫的离子转运）相关知之甚少。我们假设并观察到，在代谢率（ṀO2）受到影响且 ATP 生成受到限制的平均关键水平（Pcrit，5.4 kPa）以下的氧气分压下，离子（22Na 和 35SO4）摄取会显著减少。然而，我们惊讶地发现，在氧气分压远高于 Pcrit 时，离子摄取也会显著减少，而此时ṀO2 是稳定的。例如，在 11.7 kPa 时，SO4 摄取减少了 51%，在 Pcrit（5.4 kPa）时减少了 82%，而 Na 摄取减少了 19%，在 Pcrit 时减少了 60%。在低氧环境中停留时间更长的若虫，其离子摄取率下降幅度更大。来自全身匀浆的液体在最缺氧的条件下表现出 29%的渗透压降低。在不断变化的 PO2 条件下，非典型鸟苷酸环化酶（gcy-88e）的差异表达为其作为氧气传感器的潜在作用提供了证据。一些离子转运基因（如氯离子通道和钠钾 ATP 酶）和与缺氧相关的基因（如 ldh 和 egl-9）也受到氧气供应减少的影响。总的来说，我们工作的结果表明，N. triangulifer 能够感知氧气供应的减少，并且可能会相应地节约能量，即使ṀO2 不受影响。
