Gilmour K, Henry R, Wood C, Perry S
J Exp Biol. 1997;200(Pt 1):173-83. doi: 10.1242/jeb.200.1.173.
The electrometric [Delta]pH method and an in vitro radioisotopic HCO3- dehydration assay were used to demonstrate the presence of true extracellular carbonic anhydrase (CA) activity in the blood of the Pacific spiny dogfish Squalus acanthias. An extracorporeal circulation and stopflow technique were then used to characterise the acidbase disequilibrium in the arterial (postbranchial) blood. During the stopflow period, arterial pH (pHa) decreased by 0.028±0.003 units (mean ± s.e.m., N=27), in contrast to the increase in pHa of 0.029±0.006 units (mean ± s.e.m., N=6) observed in seawater-acclimated rainbow trout Oncorhynchus mykiss under similar conditions. The negative disequilibrium in dogfish blood was abolished by the addition of bovine CA to the circulation, while inhibition by benzolamide of extracellular and gill membrane-bound CA activities reversed the direction of the acidbase disequilibrium such that pHa increased by 0.059±0.016 units (mean ± s.e.m., N=6) during the stopflow period. When the CA activity of red blood cells (rbcs) was additionally inhibited using acetazolamide, the magnitude of the negative disequilibrium was increased significantly to -0.045±0.007 units (mean ± s.e.m., N=6). Blockage of the rbc Cl-/HCO3- exchanger using 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) also increased the magnitude of the negative disequilibrium, in this case to -0.089±0.008 units (mean ± s.e.m., N=6). Exposure of dogfish to hypercapnia had no effect on the disequilibrium, whereas the disequilibrium was significantly larger under hypoxic conditions, at -0.049±0.008 units (mean ± s.e.m., N=6). The results are interpreted within a framework in which the absence of a positive CO2 excretion disequilibrium in the arterial blood of the spiny dogfish is attributed to the membrane-bound and extracellular CA activities. The negative disequilibrium may arise from the continuation of Cl-/HCO3- exchange in the postbranchial blood and/or the hydration of CO2 added to the plasma postbranchially. Two possible sources of this CO2 are discussed; rbc CO2 production or the admixture of blood having 'low' and 'high' CO2 tensions, i.e. the mixing of postbranchial blood with blood which has bypassed the respiratory exchange surface.
采用电动ΔpH法和体外放射性同位素HCO₃⁻脱水测定法，证实了太平洋刺鲨（Squalus acanthias）血液中存在真正的细胞外碳酸酐酶（CA）活性。然后利用体外循环和停流技术来表征动脉（鳃后）血液中的酸碱失衡情况。在停流期间，动脉血pH（pHa）下降了0.028±0.003个单位（平均值±标准误，N = 27），相比之下，在类似条件下，海水驯化的虹鳟（Oncorhynchus mykiss）的pHa升高了0.029±0.006个单位（平均值±标准误，N = 6）。向循环系统中添加牛CA可消除刺鲨血液中的负失衡，而苯甲酰胺对细胞外和鳃膜结合CA活性的抑制作用则逆转了酸碱失衡的方向，使得在停流期间pHa升高了0.059±0.016个单位（平均值±标准误，N = 6）。当使用乙酰唑胺进一步抑制红细胞（rbc）的CA活性时，负失衡的幅度显著增加至-0.045±0.007个单位（平均值±标准误，N = 6）。使用4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS）阻断rbc的Cl⁻/HCO₃⁻交换器也增加了负失衡的幅度，在这种情况下达到-0.089±0.008个单位（平均值±标准误，N = 6）。将刺鲨暴露于高碳酸血症环境中对失衡情况没有影响，而在低氧条件下失衡情况显著更大，为-0.049±0.008个单位（平均值±标准误，N = 6）。这些结果是在一个框架内进行解释的，在该框架中，刺鲨动脉血中不存在正的CO₂排泄失衡归因于膜结合和细胞外CA活性。负失衡可能源于鳃后血液中Cl⁻/HCO₃⁻交换的持续进行和/或鳃后添加到血浆中的CO₂的水合作用。讨论了这种CO₂的两个可能来源；rbc产生的CO₂或具有“低”和“高”CO₂张力的血液的混合，即鳃后血液与绕过呼吸交换表面的血液的混合。
