Sanchez A P, Giusti H, Bassi M, Glass M L
Department of Physiology, Faculty of Medicine of Ribeirao Preto, University of Sao Paulo, 14.049-900 Ribeirao Preto, Sao Paulo, Brazil.
Physiol Biochem Zool. 2005 Nov-Dec;78(6):908-15. doi: 10.1086/432859. Epub 2005 Sep 27.
The South American lungfish (Lepidosiren paradoxa) has well-developed lungs and highly reduced gills. To evaluate acid-base regulation, we applied hypercarbia while blood gases and pulmonary ventilation were measured for up to 48 h. Dorsal aortic blood was analyzed, and pulmonary ventilation was measured by pneumotachography. Two protocols were used: (1) normocarbia (control) followed by aquatic hypercarbia (7% CO2 approximately 49 mmHg), gas phase normocarbic; and (2) normocarbia (control) followed by combined aquatic/gas phase hypercarbia (7% CO2). Normocarbic values were pHa~7.5, Paco2 approximately 17 mmHg, and [HCO-3]pl approximately 22 mM. For protocol 1, the first hour of exposure increased Paco2 from 17.0 to 37.4 mmHg, and pHa fell to 7.21 and remained there for the rest of the experiment. At 3 h, pulmonary ventilation reached sixfold the normocarbic value but then decreased. For protocol 2, combined gas phase/water hypercarbia had a large effect on acid-base status. Thus, Paco2 increased gradually to 74 mmHg (pHa=7.15) at 48 h. At 3 h, ventilation reached a sixfold increase relative to normocarbic control but then rose further to a 60-fold peak at 6 h, followed by a gradual decline. As in some salamanders and air-breathing teleosts, there was no evidence of active extracellular modulation bicarbonate.
南美肺鱼（Lepidosiren paradoxa）拥有发育良好的肺和高度退化的鳃。为了评估酸碱调节，我们在测量血气和肺通气长达48小时的同时施加高碳酸血症。分析背主动脉血，并通过呼吸流速描记法测量肺通气。使用了两种方案：（1）常碳酸血症（对照），随后是水生高碳酸血症（7%二氧化碳，约49 mmHg），气相常碳酸血症；（2）常碳酸血症（对照），随后是水生/气相联合高碳酸血症（7%二氧化碳）。常碳酸血症值为pHa~7.5，Paco2约17 mmHg，[HCO-3]pl约22 mM。对于方案1，暴露的第一个小时使Paco2从17.0 mmHg增加到37.4 mmHg，pHa降至7.21，并在实验的其余时间保持在该水平。在3小时时，肺通气达到常碳酸血症值的六倍，但随后下降。对于方案2，气相/水联合高碳酸血症对酸碱状态有很大影响。因此，在48小时时Paco2逐渐增加到74 mmHg（pHa = 7.15）。在3小时时，通气相对于常碳酸血症对照增加到六倍，但随后在6小时时进一步上升到60倍的峰值，随后逐渐下降。与一些蝾螈和空气呼吸硬骨鱼一样，没有证据表明存在活性细胞外调节碳酸氢盐。
