Panov A V, Scaduto R C
Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033, USA.
Am J Physiol. 1996 Apr;270(4 Pt 2):H1398-406. doi: 10.1152/ajpheart.1996.270.4.H1398.
Oxidative metabolism in the heart is tightly coupled to mechanical work. Because this coupling process is believed to involve Ca2+, the roles of mitochondrial Ca2+ in the regulation of oxidative phosphorylation was studied in isolated rat heart mitochondria. The electrical component of the mitochondrial membrane potential (delta psi) and the redox state of the pyridine nucleotides were determined during the oxidation of various substrates under different metabolic states. In the absence of added adenine nucleotides, the NADP+ redox couple was almost completely reduced, regardless of the specific substrate and the presence of Ca2+, whereas NAD+ couple redox state was highly dependent on the substrate type and the presence of Ca2+. Titration of respiration with ADP, in the presence of excess hexokinase and glucose, showed that both respiration and NAD(P)+ reduction were very sensitive to ADP. The maximal enzyme reaction rate of ADP-stimulated respiration Michaelis constants (Km) for ADP were dependent on the particular substrate employed. delta psi was much less sensitive to ADP. With either alpha-ketoglutarate or glutamate as substrate, Ca2+ significantly increased reduction of NAD(P)+.Ca2+ did not influence NAD(P)+ reduction with either acetylcarnitine or pyruvate as substrate. In the presence of ADP, delta psi was increased by Ca2+ at all metabolic states with glutamate plus malate, 0.5 mM alpha-ketoglutarate plus malate, or pyruvate plus malate as substrates. The data presented support the hypothesis that cardiac respiration is controlled by the availability of both Ca2+ and ADP to mitochondria. The data indicate that an increase in substrate supply to mitochondria can increase mitochondrial respiration at given level of ADP. This effect can be produced by Ca2+ with substrates such as glutamate, which utilize alpha-ketoglutarate dehydrogenase activity for oxidation. Increases in respiration by Ca2+ may mitigate an increase in ADP during periods of increased cardiac work.
心脏中的氧化代谢与机械功紧密相关。由于认为这种偶联过程涉及Ca2+，因此在分离的大鼠心脏线粒体中研究了线粒体Ca2+在氧化磷酸化调节中的作用。在不同代谢状态下氧化各种底物的过程中，测定了线粒体膜电位（δψ）的电学成分和吡啶核苷酸的氧化还原状态。在不添加腺嘌呤核苷酸的情况下，无论特定底物和Ca2+的存在与否，NADP+氧化还原对几乎完全还原，而NAD+对氧化还原状态高度依赖于底物类型和Ca2+的存在。在存在过量己糖激酶和葡萄糖的情况下，用ADP滴定呼吸作用表明，呼吸作用和NAD(P)+还原对ADP都非常敏感。ADP刺激的呼吸作用的最大酶反应速率和ADP的米氏常数（Km）取决于所使用的特定底物。δψ对ADP的敏感性要低得多。以α-酮戊二酸或谷氨酸为底物时，Ca2+显著增加NAD(P)+的还原。以乙酰肉碱或丙酮酸为底物时，Ca2+不影响NAD(P)+的还原。在存在ADP的情况下，以谷氨酸加苹果酸、0.5 mMα-酮戊二酸加苹果酸或丙酮酸加苹果酸为底物时，在所有代谢状态下Ca2+都会增加δψ。所提供的数据支持这样的假设，即心脏呼吸受线粒体中Ca2+和ADP可用性的控制。数据表明，在给定的ADP水平下，增加向线粒体的底物供应可以增加线粒体呼吸。这种效应可以由Ca2+与诸如谷氨酸等底物产生，谷氨酸利用α-酮戊二酸脱氢酶活性进行氧化。在心脏工作增加期间，Ca2+引起的呼吸增加可能减轻ADP的增加。
