Department of Biology, University of Ottawa , Ottawa, Ontario , Canada.
Am J Physiol Regul Integr Comp Physiol. 2019 Mar 1;316(3):R255-R264. doi: 10.1152/ajpregu.00315.2018. Epub 2019 Jan 2.
Purely diffusive O transport typically is insufficient to sustain aerobic metabolism in most multicellular organisms. In animals that are small enough, however, a high surface-to-volume ratio may allow passive diffusion alone to supply sufficient O transfer. The purpose of this study was to explore the impacts of internal convection on respiratory gas transfer in a small complex organism, the larval zebrafish ( Danio rerio). Specifically, we tested the hypothesis that internal convection is required for the normal transfer of the respiratory gases O and CO and maintenance of resting aerobic metabolic rate in larvae at 4 days postfertilization (dpf). Morpholino knockdown of the vascular endothelial growth factor (VEGF) or cardiac troponin T (TNNT2) proteins allowed an examination of gas transfer in two independent models lacking internal convection. With the use of a scanning micro-optrode technique to measure regional epithelial O fluxes ( Jo), it was demonstrated that larvae lacking convection exhibited reduced Jo in regions spanning the head to the trunk. Moreover, the acute loss of internal convection caused by heart stoppage resulted in reduced rates of cutaneous Jo, an effect that was reversed upon the restoration of internal convection. With the use of whole body respirometry, it was shown that loss of internal convection was associated with reduced resting rates of O consumption and CO excretion in larvae at 4 dpf. The results of these experiments clearly demonstrate that internal convection is required to maintain resting rates of respiratory gas transfer in larval zebrafish.
单纯的扩散 O 运输通常不足以维持大多数多细胞生物的有氧代谢。然而，对于足够小的动物，高的表面积与体积比可能允许仅通过被动扩散来提供足够的 O 传递。本研究的目的是探索内部对流对小型复杂生物（斑马鱼幼虫）呼吸气体传递的影响。具体而言，我们检验了以下假说，即内部对流对于正常的呼吸气体 O 和 CO 传递以及维持在受精后 4 天（dpf）的幼虫的静息有氧代谢率是必需的。血管内皮生长因子（VEGF）或肌钙蛋白 T（TNNT2）蛋白的形态发生素敲低允许在两个独立的缺乏内部对流的模型中检查气体传递。使用扫描微电极技术来测量区域上皮 O 通量（Jo），结果表明缺乏对流的幼虫在头部到躯干的区域中表现出减少的 Jo。此外，心脏骤停引起的内部对流的急性丧失导致皮肤 Jo 速率降低，而当恢复内部对流时，该效应被逆转。使用全身呼吸计，结果表明在 4 dpf 的幼虫中，内部对流的丧失与 O 消耗和 CO 排泄的静息速率降低有关。这些实验的结果清楚地表明，内部对流对于维持斑马鱼幼虫的呼吸气体传递的静息速率是必需的。
