Turvey S E, Allen D G
Department of Physiology, University of Sydney, NSW, Australia.
Cardiovasc Res. 1994 Jul;28(7):987-93. doi: 10.1093/cvr/28.7.987.
The free myoplasmic sodium concentration ([Na+]i) is thought to change during acidosis and ischaemia in the mammalian heart. Although there are methods available for measuring [Na+]i in isolated cells or small preparations, none is very effective in the isolated heart, which is one of the best models for studying ischaemia. The use of a fluorescent sodium indicator, sodium binding benzofuran isophthalate (SBFI), to measure [Na+]i in the isolated, perfused rat heart is described. This method was used to estimate the activity of the Na/H exchanger under conditions resembling some aspects of ischaemia.
The acetoxymethyl ester of SBFI was loaded into the perfused rat heart via the perfusate. Fluorescence signals developed on loading and were shown to be [Na+]i sensitive. An in vivo calibration technique allowed the fluorescence signals to be converted to [Na+]i.
The [Na+]i under control conditions was 6.4 mM. When the hearts were exposed to 20 mM lactate at the normal extracellular pH (pHo = 7.4) for 10 min, developed pressure fell abruptly and then slowly recovered [Na+]i rose slowly by 1.5 mM during lactate exposure and paralleled the recovery of pressure. Exposure to lactate at reduced extracellular pH (pHo = 6.4) produced a larger rise in [Na+]i. In the presence of the Na/H exchange inhibitor 5-(N-methyl-N-isobutyl)-amiloride exposure to lactate caused a small fall in [Na+]i at pHo 7.4 and 6.4.
The advantages and disadvantages of SBFI as an [Na+]i indicator in the perfused heart are described. The Na/H exchanger is an important regulator of [Na+]i during lactate induced intracellular acidosis, and it remains active in the presence of a substantial extracellular acidosis. This shows that low pHo does not necessarily inhibit the Na/H exchanger. The use of SBFI to estimate [Na+]i in the perfused heart is novel and has considerable potential for studies of ischaemia and related conditions.
人们认为，在哺乳动物心脏发生酸中毒和缺血时，肌浆内游离钠浓度（[Na⁺]i）会发生变化。虽然有一些方法可用于测量分离细胞或小组织样本中的[Na⁺]i，但在分离的心脏中，这些方法都不太有效，而分离的心脏是研究缺血的最佳模型之一。本文描述了使用荧光钠指示剂——钠结合苯并呋喃间苯二甲酸酯（SBFI）来测量分离的灌注大鼠心脏中的[Na⁺]i。该方法用于评估在类似于缺血某些方面的条件下钠/氢交换体的活性。
SBFI的乙酰氧基甲酯通过灌注液加载到灌注的大鼠心脏中。加载时产生荧光信号，且显示对[Na⁺]i敏感。一种体内校准技术可将荧光信号转换为[Na⁺]i。
对照条件下的[Na⁺]i为6.4 mM。当心脏在正常细胞外pH值（pHo = 7.4）下暴露于20 mM乳酸10分钟时，心脏的舒张期压力突然下降，然后缓慢恢复，[Na⁺]i在乳酸暴露期间缓慢升高1.5 mM，并与压力的恢复平行。在细胞外pH值降低（pHo = 6.4）的情况下暴露于乳酸会使[Na⁺]i有更大幅度的升高。在存在钠/氢交换抑制剂5-（N-甲基-N-异丁基）-氨氯吡脒的情况下，在pHo 7.4和6.4时暴露于乳酸会导致[Na⁺]i略有下降。
描述了SBFI作为灌注心脏中[Na⁺]i指示剂的优缺点。在乳酸诱导的细胞内酸中毒期间，钠/氢交换体是[Na⁺]i的重要调节因子，并且在存在大量细胞外酸中毒的情况下它仍保持活性。这表明低pHo不一定会抑制钠/氢交换体。使用SBFI评估灌注心脏中的[Na⁺]i是一种新方法，在缺血及相关病症的研究中具有相当大的潜力。
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