Bevensee Mark O, Boron Walter F
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA.
Brain Res. 2008 Feb 8;1193:143-52. doi: 10.1016/j.brainres.2007.12.002. Epub 2007 Dec 8.
We used the pH-sensitive dye BCECF to evaluate the effect of acute (5-10 min) hypoxia (approximately 3% O(2)) on the regulation of intracellular pH (pH(i)) in astrocyte populations cultured from rat hippocampus. For cells in the nominal absence of CO(2)/HCO(3)(-) at an extracellular pH of 7.40 (37 degrees C), acute hypoxia caused a small (0.05) decrease in steady-state pH(i), but increased the pH(i) recovery rate from an acid load during all but the late phase of the pH(i) recovery. During such pH(i) recoveries, the total acid extrusion rate (phi(E), the product of dpH(i)/dt and proton buffering power) decreased with increasing pH(i). Hypoxia alkali shifted the plot of phi(E) vs. pH(i); over the upper approximately 85% of the phi(E) range, this shift was 0.15-0.30. Hypoxia also stimulated the pH(i) recovery rate from an alkali load. Under normoxic conditions, switching the extracellular buffer to 5% CO(2)/22 mM HCO(-)(3) also alkali shifted the phi(E)-pH(i) plot (upper approximately 85%) by 0.4-0.5. Superimposing hypoxia on CO(2)/HCO(-)(3) further alkali shifted the phi(E)-pH(i) plot (upper approximately 85% of the phi(E) range) by 0.05-0.15. The SITS-insensitive component of phi(E) was alkali shifted by 0.20-0.30, whereas the SITS-sensitive component of phi(E) was depressed in the low pH(i) range. Thus, in the nominal absence of CO(2)/HCO(3)(-), acute hypoxia has little effect on steady-state pH(i) but stimulates acid extrusion and acid loading, whereas in the presence of CO(2)/HCO(-)(3), hypoxia stimulates the SITS-insensitive but inhibits the SITS-sensitive acid extrusion.
我们使用对pH敏感的染料BCECF来评估急性（5 - 10分钟）缺氧（约3% O₂）对从大鼠海马体培养的星形胶质细胞群体中细胞内pH（pH(i)）调节的影响。对于在细胞外pH为7.40（37℃）且名义上不存在CO₂/HCO₃⁻的情况下的细胞，急性缺氧导致稳态pH(i)出现小幅（0.05）下降，但在pH(i)恢复的除后期外的所有阶段均提高了酸负荷后的pH(i)恢复速率。在这种pH(i)恢复过程中，总酸排出速率（phi(E)，dpH(i)/dt与质子缓冲能力的乘积）随着pH(i)的升高而降低。缺氧使phi(E)与pH(i)的关系图发生碱化偏移；在phi(E)范围的上约85%，这种偏移为0.15 - 0.30。缺氧还刺激了碱负荷后的pH(i)恢复速率。在常氧条件下，将细胞外缓冲液切换为5% CO₂/22 mM HCO₃⁻也会使phi(E)-pH(i)关系图（上约85%）发生0.4 - 0.5的碱化偏移。在CO₂/HCO₃⁻存在的情况下叠加缺氧会使phi(E)-pH(i)关系图（phi(E)范围的上约85%）进一步碱化偏移0.05 - 0.15。phi(E)的SITS不敏感成分碱化偏移0.20 - 0.30，而phi(E)的SITS敏感成分在低pH(i)范围内受到抑制。因此，在名义上不存在CO₂/HCO₃⁻的情况下，急性缺氧对稳态pH(i)影响不大，但刺激酸排出和酸负荷，而在CO₂/HCO₃⁻存在的情况下，缺氧刺激SITS不敏感的酸排出但抑制SITS敏感的酸排出。
