Amin-Naves J, Giusti H, Hoffmann A, Glass M L
Department of Physiology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
Respir Physiol Neurobiol. 2007 Jan 15;155(1):35-40. doi: 10.1016/j.resp.2006.03.003. Epub 2006 Mar 22.
Lungfish are closely related to terrestrial vertebrates (tetrapoda). Like tetrapods, the South American lungfish (Lepidosiren paradoxa) has central chemoreceptors involved in regulation of acid-base status. However, no data were available on peripheral CO(2)/[H(+)] receptors. Therefore, we tested the hypothesis that such receptors exist by measuring the ventilatory responses during a 5h exposure to combined aquatic/gas phase hypercarbia 7% (approximately 49 mmHg). Normocarbic control ventilation was 22 ml BTPS kg(-1)h(-1), and hypercarbia increased ventilation to 175 ml BTPS kg(-1)h(-1) at 5h. This procedure was repeated with the modification that normocarbic mock CSF (pH 7.45; P(CO2) = 20.7 mmHg) was applied to superfuse the cerebral ventricular system during the last 2h of the experiment. This served to eliminate the hypercarbic stimulus to the central chemoreceptors, while possible responses from peripheral chemoreceptors would remain intact. Peripheral receptors were detected, since ventilation became reduced to 62 ml BTPS kg(-1)h(-1) (P<0.05), which exceeds the initial normocarbic control ventilation (P<0.05). Based on this, the peripheral contribution accounted for 20% of the total response to hypercarbia, similar to the contribution of these receptors in man.
肺鱼与陆生脊椎动物（四足动物）关系密切。与四足动物一样，南美肺鱼（南美肺鱼）具有参与酸碱平衡调节的中枢化学感受器。然而，关于外周CO(2)/[H(+)]受体的数据尚无可用信息。因此，我们通过测量在7%（约49 mmHg）的水生/气相高碳酸血症联合暴露5小时期间的通气反应，来检验此类受体存在的假设。正常碳酸血症对照通气为22 ml BTPS kg(-1)h(-1)，高碳酸血症在5小时时将通气增加至175 ml BTPS kg(-1)h(-1)。重复此过程，不同之处在于在实验的最后2小时应用正常碳酸血症模拟脑脊液（pH 7.45；P(CO2)=20.7 mmHg）来灌注脑室系统。这用于消除对中枢化学感受器的高碳酸血症刺激，而外周化学感受器的可能反应将保持完整。检测到外周受体，因为通气降至62 ml BTPS kg(-1)h(-1)（P<0.05），超过了最初的正常碳酸血症对照通气（P<0.05）。基于此，外周贡献占对高碳酸血症总反应的20%，与这些受体在人类中的贡献相似。
