Kitakaze M, Weisfeldt M L, Marban E
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
J Clin Invest. 1988 Sep;82(3):920-7. doi: 10.1172/JCI113699.
Cellular calcium overload figures prominently in the pathogenesis of the contractile dysfunction observed after brief periods of ischemia (myocardial stunning). Because acidosis is known to antagonize Ca influx and the intracellular binding of Ca, we reasoned that acidosis during reperfusion might prevent Ca overload and ameliorate functional recovery. We measured developed pressure (DP) and 31P-nuclear magnetic resonance spectra in 26 isovolumic Langendorff-perfused ferret hearts. After 15 min of global ischemia, hearts were reperfused either with normal solution (2 mM [Ca]o, Hepes-buffered, pH 7.4 bubbled with 100% O2; n = 6) or with acidic solutions (pH 6.6 during 0-3 min, pH 7.0 during 4-6 min) before returning to the normal perfusate (n = 7). Ventricular function after 30 min of reperfusion was much greater in the acidic group (105 +/- 5 mmHg at 2 mM [Ca]o) than in the unmodified reperfusion group (79 +/- 7 mmHg, P less than 0.001); similar differences in DP were found over a broad range of [Ca]o (0.5-5 mM, P less than 0.001) and during maximal Ca2+ activation (P less than 0.001). Intramyocardial pH (pHi) was lower in the acidic group than in the unmodified group during early reperfusion, but not at steady state. Phosphate compounds were comparable in both groups. To clarify whether the protective effect of acidosis is due to intracellular or extracellular pH, we produced selective intracellular acidosis during early reperfusion by exposure to 10 mM NH4Cl for 6 min just before ischemia (n = 6). For the first 12 min of reperfusion with NH4Cl-free solution (pH = 7.4), pHi was decreased relative to the unmodified group. Recovery of DP was practically complete, and maximal Ca2+-activated pressure was comparable to that in a nonischemic control group (n = 5). These results indicate that transient intracellular acidosis can prevent myocardial stunning, presumably owing to a reduction of Ca influx into cells and/or competition of H+ for intracellular Ca2+ binding sites during early reperfusion.
细胞钙超载在短暂缺血（心肌顿抑）后观察到的收缩功能障碍的发病机制中起重要作用。由于已知酸中毒可拮抗钙内流和细胞内钙结合，我们推测再灌注期间的酸中毒可能预防钙超载并改善功能恢复。我们在26个等容Langendorff灌注的雪貂心脏中测量了舒张末压力（DP）和31P-核磁共振光谱。在全心缺血15分钟后，心脏用正常溶液（2 mM [Ca]o，Hepes缓冲，pH 7.4，用100% O2鼓泡；n = 6）或酸性溶液（0 - 3分钟时pH 6.6，4 - 6分钟时pH 7.0）再灌注，然后恢复至正常灌注液（n = 7）。再灌注30分钟后的心室功能在酸性组（2 mM [Ca]o时为105±5 mmHg）比未改良再灌注组（79±7 mmHg，P < 0.001）好得多；在广泛的[Ca]o范围（0.5 - 5 mM，P < 0.001）以及最大钙激活期间（P < 0.001）发现DP有类似差异。再灌注早期酸性组的心肌内pH（pHi）低于未改良组，但在稳态时并非如此。两组的磷酸盐化合物相当。为了阐明酸中毒的保护作用是由于细胞内还是细胞外pH，我们在缺血前通过暴露于10 mM NH4Cl 6分钟在再灌注早期产生选择性细胞内酸中毒（n = 6）。在用无NH4Cl溶液（pH = 7.4）再灌注的前12分钟，pHi相对于未改良组降低。DP的恢复几乎完全，最大钙激活压力与非缺血对照组（n = 5）相当。这些结果表明，短暂的细胞内酸中毒可以预防心肌顿抑，推测是由于再灌注早期钙流入细胞减少和/或H+与细胞内钙结合位点竞争。
