Energy requirements for the Na+ gradient in the oxygenated isolated heart:: effect of changing the free energy of ATP hydrolysis
Energy requirements for the Na+ gradient in the oxygenated isolated heart:: effect of changing the free energy of ATP hydrolysis
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DOI：
10.1152/ajpheart.00534.2003
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发表时间：
2003-12-01
影响因子：
4.8
通讯作者：
Balschi, JA
中科院分区：
文献类型：
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作者：
Jansen, MA;Shen, H;Balschi, JA
本研究验证了一种假说，即当ATP水解自由能降低到某一阈值以下时，会抑制Na+-K+-ATPase(Na+泵)的活性，导致心肌细胞内Na+浓度([Na+](I))升高。设计的条件是心脏完全依赖于氧化磷酸化产生的三磷酸腺苷。唯一提供的底物是低浓度的脂肪酸丁酸酯(Bu)，0.1 mM(LowBu)，或高浓度的4 mM(HighBu)。不断增加的工作需求降低了LowBu心脏的DeltaG(ATP)。P-31、Na-23和Rb-87核磁共振波谱测量了高能磷酸盐代谢产物[Na+](I)和Rb+摄取。Rb+摄取用于评估Na+泵的活性。为了使用阳离子移动剂测定[Na+](I)，细胞外钙离子被还原到0.85 mM，这消除了工作需求DeltaG(ATP)的减少。增加细胞外Na+(Na-e(+))至200 mM恢复了工作需求增量(ATP)的减少。作为对较高[Na+](E)的反应，[Na+](I)在LowBu和HighBu心脏中同等增加，接近8.6 mM，但DeltaG(ATP)仅在LowBu心脏中下降。在最低工作负荷下，LowBu心脏DeltaG(ATP)为-53kJ/mol，Rb+摄取与HighBu心脏相似，[Na+](I)恒定。在最高工作负荷下，低Bu心脏DeltaG(ATP)降至-48kJ/mol，[Na+](I)升高至25 mM，Rb+摄取为HighBu心脏的56%。在最高的工作需求下，HighBu心脏的DeltaG(ATP)为-54kJ/mol，[Na+](I)仅增加了类似的10%。我们的结论是，低于-50kJ/mol的DeltaG(ATP)限制了Na+泵，并阻止了[Na+](I)动态平衡的维持。
This study tests the hypothesis that a decrease of the free energy of ATP hydrolysis (DeltaG(ATP)) below a threshold value will inhibit Na+-K+-ATPase (Na+ pump) activity and result in an increase of intracellular Na+ concentration ([Na+](i)) in the heart. Conditions were designed in which hearts were solely dependent on ATP derived from oxidative phosphorylation. The only substrate supplied was the fatty acid butyrate (Bu) at either low, 0.1 mM (LowBu), or high, 4 mM (HighBu), concentrations. Escalating work demand reduced the DeltaG(ATP) of the LowBu hearts. P-31, Na-23, and Rb-87 NMR spectroscopy measured high-energy phosphate metabolites, [Na+](i), and Rb+ uptake. Rb+ uptake was used to estimate Na+ pump activity. To measure [Na+](i) using a shift reagent for cations, extracellular Ca2+ was reduced to 0.85 mM, which eliminated work demand DeltaG(ATP) reductions. Increasing extracellular Na+ (Na-e(+)) to 200 mM restored work demand DeltaG(ATP) reductions. In response to higher [Na+](e), [Na+](i) increased equally in LowBu and HighBu hearts to similar to8.6 mM, but DeltaG(ATP) decreased only in LowBu hearts. At lowest work demand the LowBu heart DeltaG(ATP) was -53 kJ/mol, Rb+ uptake was similar to that of HighBu hearts, and [Na+](i) was constant. At highest work demand the LowBu heart DeltaG(ATP) decreased to -48 kJ/mol, the [Na+](i) increased to 25 mM, and Rb+ uptake was 56% of that in HighBu hearts. At the highest work demand the HighBu heart DeltaG(ATP) was -54 kJ/mol and [Na+](i) increased only similar to10%. We conclude that a DeltaG(ATP) below -50 kJ/mol limits the Na+ pump and prevents maintenance of [Na+](i) homeostasis.