Mölich Andreas, Waser Wolfgang, Heisler Norbert
Department of Animal Physiology, Humboldt-Universität zu Berlin, Berlin, Germany.
Fish Physiol Biochem. 2009 Jun;35(2):273-86. doi: 10.1007/s10695-008-9207-4. Epub 2008 Mar 10.
The physiological relevance of the teleost pseudobranch as a remnant of a reduced gill arch is still unclear. Numerous hypotheses have been proposed regarding its physiological role, but direct confirmatory evidence is lacking. The close relationship by serial blood flow arrangement with the fish eye's choroid rete has sparked the idea that pseudobranchial preconditioning of blood pH may facilitate initiation of the Root effect and thus support the establishment of high oxygen tensions for retinal diffusive supply. This idea was critically tested by studies on isolated pseudobranchs in situ (Oncorhynchus mykiss), perfused with RBC/Ringer or RBC/plasma suspensions of widely varied composition (pH 7.4-8.2). Detailed analysis of inflowing as compared to effluent perfusates indicated normal aerobic metabolism expressed by a rise in Pco2 (+0.39 +/- 0.13 mmHg x +/- SD), an oxygen utilization of 25% and a high oxygen consumption of approximately 400 nmol g(-1 ) min(-1). Upon passage of the pseudobranch, pH (corrected for Haldane effect) was only slightly acidified (-0.03 to -0.10), [HCO3(-)] and [lactate] were slightly enhanced (+0.51 mmol l(-1) or 0.13 mmol l(-1), respectively). In order to test for yet unknown plasma components involved in pseudobranch function, a second series of experiments was conducted using RBC-suspensions in fresh plasma instead of Ringer, with results closely resembling those of the RBC/Ringer series. Lacking any physiologically significant correlation with the level of perfusate pH, the obtained data indicate pseudobranchial basic metabolic activity rather than pH regulatory characteristics. Also the observed absolute changes in pH are negligible in terms of pH regulation towards the Root-threshold. Accordingly, the present experiments as well as plausibility evaluation of mechanisms do not support the idea of blood pH pre-adjustment prior to entry into the choroid rete structure of the teleost eye to facilitate the Root-mediated oxygen release.
硬骨鱼假鳃作为退化鳃弓遗迹的生理相关性仍不清楚。关于其生理作用已提出众多假说，但缺乏直接的确证证据。假鳃通过串联血流排列与鱼眼脉络膜 rete 紧密相关，这引发了一种观点，即假鳃对血液 pH 的预处理可能有助于 Root 效应的启动，从而支持为视网膜扩散供氧建立高氧张力。通过对原位分离的假鳃（虹鳟）进行研究对这一观点进行了严格测试，这些假鳃用成分差异很大（pH 7.4 - 8.2）的红细胞/林格氏液或红细胞/血浆悬浮液灌注。与流出灌注液相比，对流入灌注液的详细分析表明，通过 Pco2 升高（+0.39 +/- 0.13 mmHg x +/- SD）、25%的氧利用率和约 400 nmol g(-1 ) min(-1)的高氧消耗表现出正常的有氧代谢。假鳃通过后，pH（校正哈代效应）仅轻微酸化（-0.03 至 -0.10），[HCO3(-)]和[乳酸]略有增加（分别为+0.51 mmol l(-1)或 0.13 mmol l(-1)）。为了测试参与假鳃功能的未知血浆成分，使用新鲜血浆中的红细胞悬浮液而非林格氏液进行了第二系列实验，结果与红细胞/林格氏液系列的结果非常相似。由于所获得的数据与灌注液 pH 水平缺乏任何生理上显著的相关性，表明假鳃具有基本代谢活性而非 pH 调节特性。就调节至 Root 阈值的 pH 而言，观察到的 pH 绝对变化也可忽略不计。因此，目前的实验以及对机制的合理性评估不支持在进入硬骨鱼眼脉络膜 rete 结构之前对血液 pH 进行预调节以促进 Root 介导的氧释放这一观点。
