Balboni E, Lehninger A L
J Biol Chem. 1986 Mar 15;261(8):3563-70.
The dynamics and pathways of CO2 movements across the membranes of mitochondria respiring in vitro in a CO2/HCO-3 buffer at concentrations close to that in intact rat tissues were continuously monitored with a gas-permeable CO2-sensitive electrode. O2 uptake and pH changes were monitored simultaneously. Factors affecting CO2 entry were examined under conditions in which CO2 uptake was coupled to electrophoretic influx of K+ (in the presence of valinomycin) or Ca2+. The role of mitochondrial carbonic anhydrase (EC 4.2.1.1) in CO2 entry was evaluated by comparison of CO2 uptake by rat liver mitochondria, which possess carbonic anhydrase, versus rat heart mitochondria, which lack carbonic anhydrase. Such studies showed that matrix carbonic anhydrase activity is essential for rapid net uptake of CO2 with K+ or Ca2+. Studies with acetazolamide (Diamox), a potent inhibitor of carbonic anhydrase, confirmed the requirement of matrix carbonic anhydrase for net CO2 uptake. It was shown that at pH 7.2 the major species leaving respiring mitochondria is dissolved CO2, rather than HCO-3 or H2CO3 suggested by earlier reports. Efflux of endogenous CO2/HCO-3 is significantly inhibited by inhibitors of the dicarboxylate and tricarboxylate transport systems of the rat liver inner membrane. The possibility that these anion carriers mediate outward transport of HCO-3 is discussed.
在接近完整大鼠组织中浓度的CO₂/HCO₃缓冲液中，使用透气的CO₂敏感电极连续监测体外呼吸的线粒体膜上CO₂运动的动力学和途径。同时监测O₂摄取和pH变化。在CO₂摄取与K⁺（在缬氨霉素存在下）或Ca²⁺的电泳流入偶联的条件下，研究影响CO₂进入的因素。通过比较具有碳酸酐酶的大鼠肝脏线粒体与缺乏碳酸酐酶的大鼠心脏线粒体对CO₂的摄取，评估线粒体碳酸酐酶（EC 4.2.1.1）在CO₂进入中的作用。此类研究表明，基质碳酸酐酶活性对于通过K⁺或Ca²⁺快速净摄取CO₂至关重要。用碳酸酐酶的强效抑制剂乙酰唑胺（醋氮酰胺）进行的研究证实了基质碳酸酐酶对净CO₂摄取的需求。结果表明，在pH 7.2时，离开呼吸线粒体的主要物质是溶解的CO₂，而不是早期报告中提出的HCO₃或H₂CO₃。大鼠肝脏内膜二羧酸和三羧酸转运系统的抑制剂显著抑制内源性CO₂/HCO₃的流出。讨论了这些阴离子载体介导HCO₃向外转运的可能性。
