MR OF ENZYME ACTIVITY MEDIATING CARDIAC FUNCTION

描述（改编自申请人摘要）：拟议研究 使用磁共振波谱（MRS）来探索 缺血后心脏的心脏功能和生理化学调节。 要解决的一般问题是受损的收缩功能， 非致死性缺血后再灌注的心肌。 实验 设计的重点是糖酵解终产物的调节进入 线粒体支持心脏功能的能量需求。 一个 提出了一种方法来监测扰动之间的平衡， 分离的中间体的胞质和线粒体分布 兔心脏使用MRS。虽然缺血后的发病机制 收缩功能障碍已知是多因素的，申请人的工作 和其他人已经提出了缺血后收缩性心肌炎 线粒体关键酶丙酮酸的恢复和激活 脱氢酶（PDH）。 这种酶调节着 糖酵解终产物和配位物的氧化和非氧化命运 线粒体和线粒体之间的中间体的相对分布 胞质区室 用碳-13（13 C）标记靶向PDH 底物允许这种氧化/非氧化分布的变化， 因此，使用MRS可以在完整心脏中辨别代谢物。 13 C MRS提供了一种实验方法，使在线观察 亚细胞间的生理化学平衡。 措施 心脏性能沿着缺血后心脏的13 C MRS显示， 可以实现缺血后收缩功能障碍的代谢逆转 通过刺激PDH。 这种恢复似乎与增加的氧化有关。 糖酵解终产物，尽管另一种机制可能涉及 支链酮酸脱氢酶的活化。 这项建议 探索酶激活影响的潜在机制 再灌注期间的收缩恢复。 心脏将提供13 C 富集底物以探测酶活性， 假设：1）在再灌注时对抗抑制的PDH活性， 乳酸盐的产生，否则会通过增加乳酸盐的浓度而损害恢复 由于质子负载的能量需求; 2）活化支链 酮酸脱氢酶促进氧化代谢的恢复， 3）完整心脏的13 C NMR反映了收缩力的变化; 细胞溶质和线粒体代谢物的平衡。 实验探索 支持恢复的酶活性的调节机制 缺血后心脏

DESCRIPTION (adapted from the applicant's abstract): The proposed research uses magnetic resonance spectroscopy (MRS) to explore the link between cardiac performance and physiochemical regulation in postischemic hearts. The general problem to be addressed is the impaired contractile function of myocardium that is reperfused after non-lethal ischemia. The experimental design focuses on the regulated entry of glycolytic end products into the mitochondria in support of the energetic demands of cardiac function. An approach is proposed to monitor perturbations of the balance between the cytosolic and mitochondrial distribution of intermediates in the isolated rabbit heart using MRS. Although the pathogenesis of postischemic contractile dysfunction is known to be multifactorial, work by the applicant and others has suggested a significant link between postischemic contractile recovery and activation of the key mitochondrial enzyme pyruvate dehydrogenase (PDH). This enzyme regulates the balance between the oxidative and nonoxidative fates of glycolytic end products and coordinates the relative distribution of intermediates between the mitochondrial and cytosolic compartments. Targeting PDH with carbon-13 (13C) labeled substrates has allowed shifts in this oxidative/nonoxidative distribution of metabolites to be discerned in the intact heart with MRS. Thus, the use of 13C MRS provides an experimental approach to enable on-line observations of the physiochemical balance between subcellular compartments. Measures of cardiac performance along with 13C MRS of postischemic hearts show that metabolic reversal of postischemic contractile dysfunction can be achieved by stimulating PDH. This recovery appears related to increased oxidation of glycolytic end products, although an alternative mechanism may involve activation of the branched chain keto-acid dehydrogenase. This proposal explores potential mechanisms by which enzyme activation influences contractile recovery during reperfusion. Hearts will be supplied 13C enriched substrates to probe enzymatic activity in testing a three-fold hypothesis that: 1) countering depressed PDH activity at reperfusion avoids the production of lactate which otherwise impairs recovery via increased energetic demands due to proton load; 2) activating the branched chain keto-acid dehydrogenase promotes recovery of oxidative metabolism in support of contractility; 3) 13C NMR of intact hearts reflects changes in the balance of cytosolic and mitochondrial metabolites. Experiments explore regulatory mechanisms of enzyme activity that support the recovery of postischemic hearts.