Pressler M L
Krannert Institute of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis 46202.
Pflugers Arch. 1988 Jan;411(1):69-75. doi: 10.1007/BF00581648.
Regulation of intracellular pH (pHi) and the relationship between H+ and Ca2+ may vary during activity. Ion-selective microelectrodes were used to record pHi during action potentials of sheep Purkinje fibres prolonged by low temperature (21 degrees C) and elevated CO2 content. Intracellular pH also was measured during changes in extracellular calcium concentration, [Ca2+]o. Cytosolic alkalinization (peak pHi change, 0.03-0.05) was observed during the long action-potential plateau and transient acidification (0.01-0.02 units) upon repolarization. Potassium-induced depolarization to plateau potentials (i.e. to -15 +/- 2 mV) simulated the peak magnitude of the alkalinization. However, compensation for the alkalinization occurred at a faster rate during the action potential (8.9 +/- 4.3 nM/min) than during K+ depolarization (1.2 +/- 0.5 nM/min). In comparison, the cytoplasm acidified in resting fibres (0.06-0.07 log units) during changes of [Ca2+]o thought to increase intracellular calcium concentration. Alterations of pHi were translated into changes of proton concentration ([H+]i). Ten- to twenty-fold elevation of [Ca2+]o evoked a comparable change in [H+]i (mean increase, 5.7 nM) but oppositely directed from that during the plateau (mean decrease, 8.8 nM). The findings in resting fibres seem consistent with displacement of bound protons by Ca2+. In contrast, the initial change in pHi during the plateau is proposed to be consequent to Ca2+-release from sarcoplasmic reticulum and/or phosphocreatine hydrolysis coupled to ATP regeneration.
细胞内pH值（pHi）的调节以及H⁺与Ca²⁺之间的关系在活动过程中可能会有所不同。使用离子选择性微电极记录低温（21摄氏度）和升高的二氧化碳含量延长的绵羊浦肯野纤维动作电位期间的pHi。还在细胞外钙浓度[Ca²⁺]o变化期间测量细胞内pH值。在长动作电位平台期观察到胞质碱化（pHi峰值变化，0.03 - 0.05），复极化时出现短暂酸化（0.01 - 0.02单位）。钾诱导的去极化至平台电位（即至 - 15 ± 2 mV）模拟了碱化的峰值幅度。然而，动作电位期间对碱化的补偿速率（8.9 ± 4.3 nM/分钟）比钾去极化期间（1.2 ± 0.5 nM/分钟）更快。相比之下，在认为会增加细胞内钙浓度的[Ca²⁺]o变化期间，静息纤维中的细胞质酸化（0.06 - 0.07对数单位）。pHi的变化转化为质子浓度（[H⁺]i）的变化。[Ca²⁺]o升高10至20倍会引起[H⁺]i的类似变化（平均增加，5.7 nM），但方向与平台期相反（平均减少，8.8 nM）。静息纤维中的发现似乎与Ca²⁺置换结合质子一致。相反，平台期pHi的初始变化被认为是由于肌浆网释放Ca²⁺和/或与ATP再生偶联的磷酸肌酸水解所致。
