Belão T C, Zeraik V M, Florindo L H, Kalinin A L, Leite C A C, Rantin F T
Department of Physiological Sciences, Laboratory of Zoophysiology and Comparative Biochemistry, Federal University of São Carlos (UFSCar), P.O. Box 676, Via Washington Luis, Km 235, 13565-905 São Carlos, SP, Brazil; Joint Graduate Program in Physiological Sciences, Federal University of São Carlos, SP (UFSCar), São Paulo State University (UNESP), Araraquara, SP, Brazil.
Department of Zoology and Botany, IBILCE, São Paulo State University (UNESP), São José do Rio Preto, SP, Brazil.
Comp Biochem Physiol A Mol Integr Physiol. 2015 Sep;187:130-40. doi: 10.1016/j.cbpa.2015.05.010. Epub 2015 May 22.
We evaluated the role of the first pair of gill arches in the control of cardiorespiratory responses to normoxia and hypoxia in the air-breathing catfish, Clarias gariepinus. An intact group (IG) and an experimental group (EG, bilateral excision of first gill arch) were submitted to graded hypoxia, with and without access to air. The first pair of gill arches ablations reduced respiratory surface area and removed innervation by cranial nerve IX. In graded hypoxia without access to air, both groups displayed bradycardia and increased ventilatory stroke volume (VT), and the IG showed a significant increase in breathing frequency (fR). The EG exhibited very high fR in normoxia that did not increase further in hypoxia, this was linked to reduced O2 extraction from the ventilatory current (EO2) and a significantly higher critical O2 tension (PcO2) than the IG. In hypoxia with access to air, only the IG showed increased air-breathing, indicating that the first pair of gill arches excision severely attenuated air-breathing responses. Both groups exhibited bradycardia before and tachycardia after air-breaths. The fH and gill ventilation amplitude (VAMP) in the EG were overall higher than the IG. External and internal NaCN injections revealed that O2 chemoreceptors mediating ventilatory hypoxic responses (fR and VT) are internally oriented. The NaCN injections indicated that fR responses were mediated by receptors predominantly in the first pair of gill arches but VT responses by receptors on all gill arches. Receptors eliciting cardiac responses were both internally and externally oriented and distributed on all gill arches or extra-branchially. Air-breathing responses were predominantly mediated by receptors in the first pair of gill arches. In conclusion, the role of the first pair of gill arches is related to: (a) an elevated EO2 providing an adequate O2 uptake to maintain the aerobic metabolism during normoxia; (b) a significant bradycardia and increased fAB elicited by externally oriented O2 chemoreceptors; (c) increase in the ventilatory variables (fR and VAMP) stimulated by internally oriented O2 chemoreceptors.
我们评估了第一对鳃弓在控制呼吸空气的鲶鱼（Clarias gariepinus）对常氧和低氧的心肺反应中的作用。将完整组（IG）和实验组（EG，双侧切除第一对鳃弓）置于分级低氧环境中，有无空气可供呼吸。切除第一对鳃弓会减少呼吸表面积并消除第九对脑神经的支配。在无空气的分级低氧环境中，两组均出现心动过缓且通气冲程容积（VT）增加，IG组的呼吸频率（fR）显著增加。EG组在常氧时表现出非常高的fR，在低氧时并未进一步增加，这与从通气气流中提取的氧气减少（EO2）以及比IG组显著更高的临界氧张力（PcO2）有关。在有空气可供呼吸的低氧环境中，只有IG组表现出空气呼吸增加，表明切除第一对鳃弓严重减弱了空气呼吸反应。两组在空气呼吸前均出现心动过缓，呼吸后出现心动过速。EG组的心率（fH）和鳃通气幅度（VAMP）总体上高于IG组。外部和内部注射氰化钠表明，介导通气低氧反应（fR和VT）的氧化学感受器是向内定向的。氰化钠注射表明，fR反应主要由第一对鳃弓中的感受器介导，而VT反应由所有鳃弓上的感受器介导。引发心脏反应的感受器既有向内定向的也有向外定向的，分布在所有鳃弓或鳃外。空气呼吸反应主要由第一对鳃弓中的感受器介导。总之，第一对鳃弓的作用与以下方面有关：（a）升高的EO2，在常氧期间提供足够的氧气摄取以维持有氧代谢；（b）由向外定向的氧化学感受器引发的显著心动过缓和空气呼吸频率增加；（c）由向内定向的氧化学感受器刺激通气变量（fR和VAMP）增加。
