Schaefer S, Ramasamy R
Division of Cardiovascular Medicine, University of California Davis 95616, USA.
Cardiovasc Res. 1997 May;34(2):329-36. doi: 10.1016/s0008-6363(97)00042-4.
Pharmacologic inhibition of the Na-H exchanger prior to and during ischemia has been shown to protect the ischemic heart by reducing Na-H exchange. However, pH regulation in the ischemic heart is primarily mediated by other pH regulatory mechanisms, such as metabolite efflux and sodium-coupled HCO3-influx, which may compensate for a reduction in Na-H exchange by increasing proton efflux. We hypothesized that short-term pharmacologic inhibition of the Na-H exchanger would result in increases in other compensatory pH regulatory mechanisms and thereby limit acidosis during ischemia and reduce ischemic injury.
In order to test this hypothesis, we exposed isolated perfused rat hearts to ethylisopropylamiloride (EIPA, 3 micro M) for 40 min, followed by 10 min of EIPA-free perfusate and 30 min of global ischemia (termed CTL/EIPA hearts). The effects of this intervention were compared to hearts perfused with either glucose alone (CTL) or EIPA 3 micro M for 10 min before ischemia (EIPA). Ischemic injury was measured using creatine kinase (CK) release on reperfusion, while pH and metabolic effects were measured using 31P nuclear magnetic resonance spectroscopy. The effect of this intervention on recovery from an acid load was assessed using an NH4Cl pre-pulse in bicarbonate-containing Krebs-Henseleit as well as a HEPES buffer.
Both CTL/EIPA and EIPA hearts had marked reduction in ischemic injury (CK control 1191 +/- IU/g dry weight: CTL/EIPA 406 +/- 42 IU/gdw; EIPA 333 +/- 78 IU/gdw), as well as significantly reduced end-diastolic pressure on reperfusion. Intracellular pH was higher in the CTL/EIPA hearts (end-ischemic pH = 6.34 +/- 0.05) compared to either control (5.86 +/- 0.02) or EIPA hearts (6.01 +/- 0.02), while pH recovery on reperfusion was markedly slowed in the CTL/EIPA hearts. CTL/EIPA hearts had rapid ATP depletion during ischemia, but PCr recovery comparable to EIPA hearts. Acidification on exposure to NH4Cl was increased in the presence of HEPES, but ph recovery was not altered by short-term exposure to EIPA.
These data show that short-term inhibition of the Na-H altered pH regulation in the ischemic heart, resulting in reduced acidosis and slow pH recovery on reperfusion, coupled with reduction in ischemic injury and end-diastolic pressure on a reperfusion. These findings are consistent with short-term exposure to EIPA accelerating ATP depletion during ischemia, as well as limiting proton efflux during reperfusion.
在缺血之前及缺血期间对钠氢交换体进行药理学抑制已显示可通过减少钠氢交换来保护缺血心脏。然而，缺血心脏中的pH调节主要由其他pH调节机制介导，例如代谢产物外流和钠偶联的HCO3-内流，这些机制可能通过增加质子外流来补偿钠氢交换的减少。我们假设对钠氢交换体进行短期药理学抑制会导致其他代偿性pH调节机制增加，从而在缺血期间限制酸中毒并减少缺血性损伤。
为了验证这一假设，我们将离体灌注的大鼠心脏暴露于乙基异丙基amiloride（EIPA，3微摩尔）中40分钟，随后用不含EIPA的灌注液灌注10分钟，然后进行30分钟的全心缺血（称为CTL/EIPA心脏）。将这种干预的效果与单独用葡萄糖灌注的心脏（CTL）或在缺血前用3微摩尔EIPA灌注10分钟的心脏（EIPA）进行比较。使用再灌注时肌酸激酶（CK）的释放来测量缺血性损伤，而使用31P核磁共振波谱来测量pH和代谢效应。使用含碳酸氢盐的Krebs-Henseleit以及HEPES缓冲液中的NH4Cl预脉冲来评估这种干预对酸负荷恢复的影响。
CTL/EIPA心脏和EIPA心脏的缺血性损伤均显著降低（CK对照组1191±IU/g干重：CTL/EIPA组406±42 IU/gdw；EIPA组333±78 IU/gdw），再灌注时舒张末期压力也显著降低。与对照组（5.86±0.02）或EIPA心脏（6.01±0.02）相比，CTL/EIPA心脏的细胞内pH更高（缺血末期pH = 6.34±0.05），而CTL/EIPA心脏再灌注时的pH恢复明显减慢。CTL/EIPA心脏在缺血期间ATP快速消耗，但磷酸肌酸恢复与EIPA心脏相当。在HEPES存在的情况下，暴露于NH4Cl时的酸化增加，但短期暴露于EIPA对pH恢复没有影响。
这些数据表明，对钠氢交换体的短期抑制改变了缺血心脏中的pH调节，导致酸中毒减轻和再灌注时pH恢复减慢，同时减少了缺血性损伤和再灌注时的舒张末期压力。这些发现与短期暴露于EIPA加速缺血期间的ATP消耗以及限制再灌注期间的质子外流一致。
