Schäfer C, Ladilov Y V, Schäfer M, Piper H M
Physiologisches Institut, Justus Liebig Universität Giessen, D-35392 Giessen, Germany.
Am J Physiol Heart Circ Physiol. 2000 Nov;279(5):H2143-50. doi: 10.1152/ajpheart.2000.279.5.H2143.
We investigated the question of whether inhibition of the Na(+)/H(+) exchanger (NHE) during ischemia is protective due to reduction of cytosolic Ca(2+) accumulation or enhanced acidosis in cardiomyocytes. Additionally, the role of the Na(+)-HCO(3)(-) symporter (NBS) was investigated. Adult rat cardiomyocytes were exposed to simulated ischemia and reoxygenation. Cytosolic pH [2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)], Ca(2+) (fura 2), Na(+) [sodium-binding benzolfuran isophthatlate (SBFI)], and cell length were measured. NHE was inhibited with 3 micromol/l HOE 642 or 1 micromol/l 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), and NBS was inhibited with HEPES buffer. During anoxia in bicarbonate buffer, cells developed acidosis and intracellular Na and Ca (Na(i) and Ca(i), respectively) overload. During reoxygenation cells underwent hypercontracture (44.0 +/- 4.1% of the preanoxic length). During anoxia in bicarbonate buffer, inhibition of NHE had no effect on changes in intracellular pH (pH(i)), Na(i), and Ca(i), but it significantly reduced the reoxygenation-induced hypercontracture (HOE: 61.0 +/- 1.4%, EIPA: 68.2 +/- 1.8%). The sole inhibition of NBS during anoxia was not protective. We conclude that inhibition of NHE during anoxia protects cardiomyocytes against reoxygenation injury independently of cytosolic acidification and Ca(i) overload.
我们研究了在缺血期间抑制钠氢交换体（NHE）是否因减少心肌细胞胞质钙（Ca²⁺）蓄积或增强酸中毒而具有保护作用这一问题。此外，还研究了钠-碳酸氢根协同转运体（NBS）的作用。成年大鼠心肌细胞暴露于模拟缺血和复氧环境。测量胞质pH[2',7'-双（2-羧乙基）-5（6）-羧基荧光素（BCECF）]、Ca²⁺（fura 2）、Na⁺[钠结合苯并呋喃异邻苯二甲酸酯（SBFI）]以及细胞长度。用3 μmol/L HOE 642或1 μmol/L 5-（N-乙基-N-异丙基）-氨氯吡脒（EIPA）抑制NHE，并用HEPES缓冲液抑制NBS。在碳酸氢盐缓冲液中缺氧期间，细胞发生酸中毒以及细胞内钠和钙（分别为Na⁺i和Ca²⁺i）过载。在复氧期间，细胞发生超收缩（达到缺氧前长度的44.0±4.1%）。在碳酸氢盐缓冲液中缺氧期间，抑制NHE对细胞内pH（pH⁺i）、Na⁺i和Ca²⁺i的变化没有影响，但它显著减轻了复氧诱导的超收缩（HOE：61.0±1.4%，EIPA：68.2±1.8%）。在缺氧期间单独抑制NBS没有保护作用。我们得出结论，缺氧期间抑制NHE可保护心肌细胞免受复氧损伤，这与胞质酸化和Ca²⁺i过载无关。
