Hughes M C, Perry S F
Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, K1N6N5, Canada.
J Comp Physiol B. 2021 May;191(3):469-478. doi: 10.1007/s00360-020-01331-z. Epub 2021 Feb 12.
Oxygen uptake (ṀO) in larval zebrafish prior to maturation of the gill relies on cutaneous O transfer. Under normoxic conditions, rates of cutaneous O transfer are unaffected by haemoglobin availability but are diminished in fish lacking a functional circulatory system, suggesting that internal convection is critically involved in setting the resting ṀO in zebrafish larvae, even when relying on cutaneous O transfer. The reliance of ṀO on blood circulation led to the first objective of the current study, to determine whether loss of internal convection would reduce acute hypoxia performance (as determined by measuring critical PO; P) in larval zebrafish under conditions of moderate hypoxia (PO = 55 mmHg) at 28.5 and 34 °C. Internal convection was eliminated by preventing development of blood vessels using morpholino knockdown of vascular endothelial growth factor (VEGF); these fish are termed VEGF morphants. Breathing frequency (f) and heart rate (f) also were measured (at 28.5 °C) to determine whether any detriment in performance might be linked to cardiorespiratory dysfunction. Although ṀO was reduced in the VEGF morphants, there was no significant effect on P at 28.5 °C. Raising temperature to 34 °C resulted in the VEGF morphants exhibiting a higher P than the shams, suggesting an impairment of hypoxia tolerance in the morphants at the higher temperature. The usual robust increase in f during hypoxia was absent or attenuated in VEGF morphants at 4 and 5 days post fertilization (dpf), respectively. Resting f was reduced in the VEGF morphants and unlike the sham fish, the morphants did not exhibit hypoxic tachycardia at 4 or 5 dpf. The number of cutaneous neuroepithelial cells (presumptive O chemoreceptors) was significantly higher in the VEGF morphants and thus the cardiorespiratory impairment in the morphants during hypoxia was unlikely related to inadequate peripheral O sensing.
在鳃成熟之前，斑马鱼幼体的氧气摄取（ṀO）依赖于皮肤对氧气的转运。在常氧条件下，皮肤氧气转运速率不受血红蛋白可用性的影响，但在缺乏功能性循环系统的鱼类中会降低，这表明即使依赖皮肤氧气转运，内部对流在设定斑马鱼幼体的静息ṀO中也起着关键作用。ṀO对血液循环的依赖导致了本研究的第一个目标，即确定在28.5℃和34℃的中度缺氧（PO₂ = 55 mmHg）条件下，内部对流的丧失是否会降低斑马鱼幼体的急性缺氧表现（通过测量临界PO₂；Pcrit）。通过使用吗啉代敲低血管内皮生长因子（VEGF）来阻止血管发育，从而消除内部对流；这些鱼被称为VEGF morphants。还测量了呼吸频率（f）和心率（fH）（在28.5℃），以确定性能上的任何损害是否可能与心肺功能障碍有关。尽管VEGF morphants中的ṀO降低了，但在28.5℃时对Pcrit没有显著影响。将温度升至34℃导致VEGF morphants表现出比假手术组更高的Pcrit，这表明在较高温度下morphants的缺氧耐受性受损。在受精后4天和5天（dpf），VEGF morphants在缺氧期间通常强劲的f增加分别不存在或减弱。VEGF morphants的静息f降低，与假手术鱼不同，morphants在4或5 dpf时没有表现出缺氧性心动过速。VEGF morphants中皮肤神经上皮细胞（假定的氧气化学感受器）的数量显著更高，因此morphants在缺氧期间的心肺功能损害不太可能与外周氧气感知不足有关。
