Ionic movement and tolerance to ischemia in congenital heart disease : Sodium movement via the Na^+/H^+ exchange during reoxygenation is a determinant of post-ischemic functional recovery in the rat myocardium

目的：探讨复氧过程中Na+/H+交换抑制对心功能恢复的影响，以及Na+/HCO3^-共转运体在钠离子运动中的作用。方法：用Krebs-Henseleit碳酸氢盐缓冲液灌流大鼠离体心，常温(37℃)全心缺血20分钟后再灌流(37℃)，以确定钠离子运动是否为心功能恢复的决定因素。(1)100μ二甲基阿米洛利(DMA)在再灌流前10min(方案I)或缺氧再灌注5min(方案II)后10min给予。Ii)在再灌流的前10分钟使用无碳酸氢钠的HEPES缓冲液(方案III)。结果：1)在方案I和方案II中，DMA组缺血后左室发展压(%LVdP)恢复明显高于对照组(方案II分别为68.6±5.9和52.0±6.1%，方案II分别为66.6±2.8和52.0±5.5%)。在方案III中，无碳酸氢组与对照组相比差异无统计学意义(分别为35.9±4.9和24.7±6.7%)。结论：复氧过程中钠离子通过Na+/H+交换运动是心功能恢复的决定因素。Na~+/HCO3~+共转运体可能不参与再灌流过程中钠离子的运动。

Objectives : To determine whether or not sodium ion movement during reoxygenation is a determinant of post-ischemic recovery of cardiac function, we examined i) the effect of Na^+/H^+ exchange inhibition during reperfusion or reoxygenation on post-ischemic recovery of cardiac function and ii) the involvement of Na+/HCO_3^-cotransporter in the sodium ion movement.Methods : Isolated rat hearts were Langendorff-perfused with Krebs-Henseleit bicarbonate buffer and subjected to 20 minutes of normothermic (37C) global ischemia followed by normothermic (37℃) reperfusion. i) 100 μM dimethyl amiloride (DMA) was given during the first 10 min of reperfusion (protocol I) or for 10 minutes after 5-minute hypoxic reperfusion (protocol II). ii) a bicarbonate-free HEPES buffer was used during the first 10 minutes of reperfusion (protocol III). All the protocols were then followed by 25 minutes of noromoxic reperfusion.Results : i) In protocols I and II, the post-ischemic recovery of left ventricular developed pressure (%LVDP) was significantly greater in the DMA group than in the control group (68.6±5.9 vs. 52.0±6.1%, respectively in protocol Land 66.6±2.8 vs. 52.0±5.5%, respectively in protocol II). In protocol III, there was no difference between the bicarbonate-free group and the control group (35.9±4.9 vs. 24.7±6.7%, respectively).Conclusions : Sodium ion movement via the Na^+/H^+ exchange during reoxygenation is a determinant of post-ischemic recovery of cardiac function. The Na^+/HCO_3^- cotransporter may not be involved in the sodium ion movement during reperfusion.