Tuong Dang Diem, Borowiec Brittney, Clifford Alexander M, Filogonio Renato, Somo Derek, Huong Do Thi Thanh, Phuong Nguyen Thanh, Wang Tobias, Bayley Mark, Milsom William K
Department of Aquatic Nutrition and Products Processing, College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam.
Department of Biology, McMaster University, Hamilton, Canada.
J Comp Physiol B. 2018 Jul;188(4):581-589. doi: 10.1007/s00360-018-1150-9. Epub 2018 Mar 3.
The aim of the present study was to determine the roles of externally versus internally oriented CO/H-sensitive chemoreceptors in promoting cardiorespiratory responses to environmental hypercarbia in the facultative air-breathing fish, Chitala ornata (the clown knifefish). Fish were exposed to environmental acidosis (pH ~ 6.0) or hypercarbia (≈ 30 torr PCO) that produced changes in water pH equal to the pH levels of the acidotic water to distinguish the relative roles of CO versus H. We also injected acetazolamide to elevate arterial levels of PCO and [H] in fish in normocarbic water to distinguish between internal and external stimuli. We measured changes in gill ventilation frequency, air breathing frequency, heart rate and arterial blood pressure in response to each treatment as well as the changes produced in arterial PCO and pH. Exposure to normocarbic water of pH 6.0 for 1 h did not produce significant changes in any measured variable. Exposure to hypercarbic water dramatically increased air breathing frequency, but had no effect on gill ventilation. Hypercarbia also produced a modest bradycardia and fall in arterial blood pressure. Injection of acetazolamide produced similar effects. Both hypercarbia and acetazolamide led to increases in arterial PCO and falls in arterial pH although the changes in arterial PCO/pH were more modest following acetazolamide injection as were the increases in air breathing frequency. The acetazolamide results suggest that the stimulation of air breathing was due, at least in part, to stimulation of internally oriented CO/H chemoreceptors monitoring blood gas changes.
本研究的目的是确定外向型与内向型CO/H敏感化学感受器在兼性空气呼吸鱼类——线纹长臀鮠（小丑刀鱼）中促进对环境高碳酸血症的心肺反应中的作用。将鱼暴露于环境酸中毒（pH ~ 6.0）或高碳酸血症（≈ 30托PCO₂）中，这会使水体pH发生变化，其变化程度与酸中毒水体的pH水平相同，以区分CO与H的相对作用。我们还注射乙酰唑胺以提高常碳酸血症水体中鱼的动脉PCO₂和[H⁺]水平，以区分内部和外部刺激。我们测量了每种处理后鳃通气频率、空气呼吸频率、心率和动脉血压的变化，以及动脉PCO₂和pH的变化。将鱼暴露于pH 6.0的常碳酸血症水体中1小时，未使任何测量变量产生显著变化。暴露于高碳酸血症水体中会显著增加空气呼吸频率，但对鳃通气没有影响。高碳酸血症还会导致适度的心动过缓和动脉血压下降。注射乙酰唑胺产生了类似的效果。高碳酸血症和乙酰唑胺均导致动脉PCO₂升高和动脉pH下降，尽管注射乙酰唑胺后动脉PCO₂/pH的变化以及空气呼吸频率的增加更为适度。乙酰唑胺的结果表明，空气呼吸的刺激至少部分归因于对监测血气变化的内向型CO/H化学感受器的刺激。
