Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC, Canada.
J Comp Physiol B. 2010 Apr;180(4):521-30. doi: 10.1007/s00360-009-0438-1. Epub 2010 Jan 1.
Carbon dioxide (CO(2)) transport in the blood of fishes is aided by the proton-binding properties of hemoglobin (Hb) through either a high-intrinsic buffer value and small oxylabile proton binding (Haldane effect), or a low buffer value and large Haldane effect. Primitive species, such as elasmobranchs and sarcopterygians have been shown to rely on the former, while derived species, such as teleosts rely on the latter. Both strategies are effective in the transport of CO(2) in the blood. However, there is a paucity of information on the nature of the transition between these two strategies that appears to occur within the intermediate group of fishes, the basal actinopterygians. The objective of the present study was to simultaneously assess the intrinsic Hb buffer values and Haldane effects of species within the basal actinopterygian lineage to characterize the transition in Hb-proton-binding strategy seen among the fishes. Expressed in order of most basal to most derived, the species investigated included American paddlefish (Polyodon spathula), white sturgeon (Acipenser transmontanus), spotted gar (Lepisosteus oculatus), alligator gar (Atractosteus spatula), bowfin (Amia calva), and mooneye (Hiodon tergisus). Hemolysates from these species were prepared and Hb titrations (under oxygenated and deoxygenated conditions) were performed in both the presence and absence of saturating levels of organic phosphates (GTP). The findings suggest that the nature of the Hb-proton-binding transition may have been punctuated rather than gradual, with the Hb buffer value decreasing and the Haldane effect increasing significantly in bowfin from fairly steady ancestral levels in the four more basal species. This change is coupled with the initial appearance of the choroid rete, as well as an increase in the magnitude and onset pH of the Root effect in bowfin, suggesting that the change in Hb-proton-binding strategy may be associated with the evolution of enhanced O(2) delivery to the eye and an in vivo operational Root effect.
鱼类血液中的二氧化碳（CO(2)）运输得益于血红蛋白（Hb）的质子结合特性，这可以通过高固有缓冲值和小的可氧化质子结合（Haldane 效应），或低缓冲值和大的 Haldane 效应来实现。已证实，原始物种（如软骨鱼和肉鳍鱼）依赖前者，而衍生物种（如硬骨鱼）依赖后者。这两种策略在血液中 CO(2)的运输中都很有效。然而，关于这两种策略之间的过渡性质的信息很少，而这种过渡似乎发生在中间组鱼类——基干肉鳍鱼中。本研究的目的是同时评估基干肉鳍鱼谱系内物种的固有 Hb 缓冲值和 Haldane 效应，以描述鱼类中 Hb-质子结合策略的转变。按照从最基础到最衍生的顺序，所研究的物种包括美洲匙吻鲟（Polyodon spathula）、白鲟（Acipenser transmontanus）、斑点叉尾鮰（Lepisosteus oculatus）、鳄雀鳝（Atractosteus spatula）、弓鳍鱼（Amia calva）和北美狗鱼（Hiodon tergisus）。从这些物种中提取血红细胞并制备血红蛋白，在有氧和无氧条件下进行 Hb 滴定（在存在和不存在饱和水平有机磷酸盐（GTP）的情况下）。研究结果表明，Hb-质子结合转变的性质可能是间断的而不是渐进的，与四个更基础的物种相比， bowfin 的 Hb 缓冲值显著降低，Haldane 效应显著增加。这种变化伴随着脉络膜网的最初出现，以及 bowfin 中 Root 效应的幅度和起始 pH 值的增加，这表明 Hb-质子结合策略的改变可能与增强向眼睛供氧以及体内操作 Root 效应的进化有关。
