Sheldon Claire, Church John
Department of Physiology, University of British Columbia, Vancouver, British Columbua, Canada.
J Neurochem. 2004 Feb;88(3):594-603. doi: 10.1046/j.1471-4159.2003.02169.x.
The effect of anoxia on Na+/H+ exchange activity was examined in acutely isolated adult rat hippocampal CA1 neurons loaded with the H+-sensitive fluorophore, BCECF. Five-minute anoxia imposed under nominally HCO3-/CO2-free conditions induced a fall in pHi, the magnitude of which was smaller following prolonged exposure to medium in which N-methyl-D-glucamine (NMDG+) was employed as an extracellular Na+ (Na(+)(o)) substitute. Also consistent with the possibility that Na+/H+ exchange becomes inhibited soon after the induction of anoxia, rates of Na(+)(o)-dependent pHi recovery from internal acid loads imposed during anoxia were slowed, compared to rates of Na(+)(o)-dependent pHi recovery observed prior to anoxia. At the time at which rates of pHi recovery were reduced during anoxia, cellular adenosine triphosphate (ATP) levels had fallen to 35% of preanoxic levels, suggesting that ATP depletion might contribute to the observed inhibition of Na+/H+ exchange. In support, incubation of neurons with 2-deoxyglucose and antimycin A under normoxic conditions induced a fall in cellular ATP levels that was also associated with reduced Na(+)(o)-dependent rates of pHi recovery from imposed acid loads; conversely, pre-treatment with 10 mm creatine attenuated the effects of anoxia to reduce both ATP levels and Na(+)(o)-dependent rates of pHi recovery from internal acid loads. Taken together, the results are consistent with the possibility that functional Na+/H+ exchange activity in adult rat CA1 neurons declines soon after the onset of anoxia, possibly as a result of anoxia-induced falls in intracellular ATP.
在急性分离的成年大鼠海马CA1神经元中，使用对H⁺敏感的荧光染料羧基荧光素乙酰甲酯（BCECF）加载，研究缺氧对Na⁺/H⁺交换活性的影响。在名义上无HCO₃⁻/CO₂的条件下施加5分钟的缺氧会导致细胞内pH值（pHi）下降，在长时间暴露于用N-甲基-D-葡萄糖胺（NMDG⁺）作为细胞外Na⁺（Na⁺(o)）替代物的培养基后，pHi下降的幅度较小。这也与缺氧诱导后Na⁺/H⁺交换很快被抑制的可能性一致，与缺氧前观察到的Na⁺(o)依赖的pHi从内部酸负荷恢复的速率相比，缺氧期间施加内部酸负荷后Na⁺(o)依赖的pHi恢复速率减慢。在缺氧期间pHi恢复速率降低时，细胞三磷酸腺苷（ATP）水平已降至缺氧前水平的35%，这表明ATP耗竭可能导致观察到的Na⁺/H⁺交换抑制。作为支持，在常氧条件下用2-脱氧葡萄糖和抗霉素A孵育神经元会导致细胞ATP水平下降，这也与从施加的酸负荷中恢复的Na⁺(o)依赖的pHi速率降低有关；相反，用10 mM肌酸预处理可减弱缺氧对降低ATP水平和从内部酸负荷中恢复的Na⁺(o)依赖的pHi速率的影响。综上所述，这些结果与成年大鼠CA1神经元中的功能性Na⁺/H⁺交换活性在缺氧开始后很快下降的可能性一致，这可能是缺氧诱导的细胞内ATP下降的结果。
