Docherty J C, Yang L, Pierce G N, Deslauriers R
Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada.
Mol Cell Biochem. 1997 Nov;176(1-2):257-64.
To help resolve the controversy as to whether or not Na(+)-H+ exchange is functioning during reperfusion of the ischemic myocardium we assessed the effects of dimethylamiloride (DMA, an amiloride analogue possessing selectivity for inhibition of the Na(+)-H+ exchanger) on cardiac function and intracellular pH during ischemia-reperfusion. Studies were performed in the presence of bicarbonate (modified Krebs-Henseleit buffer) or in the nominal absence of bicarbonate (HEPES buffer) in order to determine if similar cardioprotection and effects on intracellular pH were observed in the presence and absence of bicarbonate dependent transport processes. Isovolumic rat hearts were perfused in the Langendorff mode at a constant pressure of 80 mm Hg and subjected to 28 min total global ischemia at 37 degrees C. Intracellular pH was determined from the pH dependent shift of the inorganic phosphate peak in 31P nuclear magnetic resonance spectra. DMA (20 microM) was infused for either 2.5 min before ischemia, for the initial 5 min of reperfusion, or at both time intervals. DMA had no effect on the intracellular pH during ischemia. Intracellular pH returned to pre-ischemic levels within 2.5 min of reperfusion in bicarbonate buffer. This normalization of pH was slower in HEPES perfusate. In both bicarbonate and HEPES perfused hearts all drug dosing regimens caused a significant increase in the recovery of mechanical function after reperfusion and slowed the recovery of intracellular pH during reperfusion. These results suggest that the Na(+)-H+ exchanger is activated during reperfusion of the ischemic myocardium, that this activation of the exchanger contributes to ischemia-reperfusion induced cardiac dysfunction and that administration of an inhibitor of Na(+)-H+ exchange at reperfusion significantly attenuates the deleterious effects of exchanger activation.
为了帮助解决关于缺血心肌再灌注期间Na(+)-H+交换是否起作用的争议，我们评估了二甲基氨氯吡脒（DMA，一种对抑制Na(+)-H+交换器具有选择性的氨氯吡脒类似物）对缺血-再灌注期间心脏功能和细胞内pH的影响。研究在存在碳酸氢盐（改良的克雷布斯-亨泽莱特缓冲液）或名义上不存在碳酸氢盐（HEPES缓冲液）的情况下进行，以确定在存在和不存在依赖碳酸氢盐的转运过程时是否观察到类似的心脏保护作用和对细胞内pH的影响。将等容大鼠心脏在Langendorff模式下以80 mmHg的恒定压力灌注，并在37℃下进行28分钟的全心缺血。通过31P核磁共振谱中无机磷酸峰的pH依赖性位移来测定细胞内pH。DMA（20 μM）在缺血前输注2.5分钟、在再灌注的最初5分钟或在两个时间间隔输注。DMA在缺血期间对细胞内pH没有影响。在碳酸氢盐缓冲液中，再灌注2.5分钟内细胞内pH恢复到缺血前水平。在HEPES灌注液中，pH的这种正常化较慢。在碳酸氢盐和HEPES灌注的心脏中，所有给药方案在再灌注后均导致机械功能恢复显著增加，并减慢了再灌注期间细胞内pH的恢复。这些结果表明，缺血心肌再灌注期间Na(+)-H+交换器被激活，这种交换器的激活导致缺血-再灌注诱导的心脏功能障碍，并且在再灌注时给予Na(+)-H+交换抑制剂可显著减轻交换器激活的有害影响。
