MR OF ENZYME ACTIVITY MEDIATING CARDIAC FUNCTION

描述(改编自申请人的摘要)：拟议的研究 使用磁共振波谱(MRS)来探索两者之间的联系 缺血后心脏的心功能和理化调节。 需要解决的一般问题是心脏收缩功能受损。 非致命性缺血后再灌流的心肌。实验性的 设计的重点是糖酵解最终产物进入 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控 中间产物的胞浆和线粒体分布 应用MRS对兔心脏缺血后发病机制的研究 收缩功能障碍是已知的多因素的，由申请者工作 另一些人则认为缺血后的收缩与 线粒体关键酶丙酮酸的回收和激活 脱氢酶(PDH)。这种酶调节两种物质之间的平衡 糖酵解终产物和配位化合物的氧化和非氧化命运 线粒体和线粒体之间中间体的相对分布 胞质隔间。碳-13(13C)标记的PDH靶向 底物允许这种氧化/非氧化分布的变化 代谢物要在完整的心脏中辨别，因此，使用 ~(13)C-MRS提供了一种实验方法，能够在线观察 亚细胞室之间的物理化学平衡。衡量标准 缺血后心脏的心功能和~(13)C MRS显示 缺血后收缩功能障碍的代谢逆转是可以实现的 通过刺激PDH。这一恢复似乎与增加的氧化 糖酵解最终产物，尽管另一种机制可能涉及 支链酮酸脱氢酶的激活。这项建议 探索酶激活影响的潜在机制 再灌流期间的收缩恢复。心脏将供应13C 富集底物用于检测酶活性的三倍 假设：1)对抗再灌流时PDH活性的抑制可避免 乳酸的产生，否则会因增加乳酸而损害恢复。 质子负荷引起的能量需求；2)激活支链 酮酸脱氢酶促进载体氧化代谢的恢复 3)完整心脏的~(13)C核磁共振反应 胞质和线粒体代谢物的平衡。实验探索 支持细胞复苏的酶活性调节机制 缺血后的心脏。

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.