el Alaoui-Talibi Z, Moravec J
Laboratoire d'Energétique et de Cardiologie Cellulaire de L'INSERM, UER de Médecine et de Pharmacie, Dijon, France.
Biochim Biophys Acta. 1989 Jun 8;1003(2):109-14. doi: 10.1016/0005-2760(89)90242-7.
L-Carnitine transport and free fatty acid oxidation have been studied in hearts of rats with 3-month-old aorto-caval fistula. For carnitine transport experiments, the hearts were perfused via the ascending aorta with a bicarbonate buffer containing 11 mM glucose and variable concentrations L-[14C]carnitine (10-200 microM). In some experiments, the active component of carnitine transport was suppressed by the adjunction of 0.05 mM mersalyl acid. The subtraction of passive from total transport allowed reconstruction of the saturation curves of the carrier-mediated transport of L-carnitine. Our data suggest that at a physiological carnitine concentration (50 microM), the rate of [14C]carnitine accumulation was significantly depressed in mechanically overloaded hearts. In addition, according to Lineweaver-Burk analysis, the affinity of the membrane carrier for L-carnitine was considerably diminished (Km carnitine 125 instead of 83 microM, Vmax unchanged). The above alterations of L-carnitine transport did not result from a decrease of the transmembrane gradient of sodium, since the intracellular Na+ content of the hypertrophied hearts was quite similar to that of control hearts. The ability of atrially perfused, working hearts to oxidize the exogenous free fatty acids was assessed from 14CO2 production obtained in the presence of [U-14C]palmitate or [1-14C]octanoate. The total 14CO2 production, expressed per min per g dry weight, was significantly diminished in hearts from rats with the aorto-caval fistula if 1.2 mM palmitate was used. On the other hand, in the presence of 2.4 mM octanoate, a substrate which circumvents the carnitine-acylcarnitine translocase, no such reduction of the 14CO2 production could be detected. Our results suggest that the decrease of L-carnitine transport, resulting in a significant depression of tissue carnitine, may impair long-chain fatty acid activation and/or translocation into mitochondria. In contrast, the oxidation of short-chain fatty acids, the activation of which takes place directly in mitochondrial matrix, is not limited in volume-overloaded hearts.
对3月龄大鼠主动脉-腔静脉瘘心脏的左旋肉碱转运和游离脂肪酸氧化进行了研究。在左旋肉碱转运实验中，通过升主动脉用含有11 mM葡萄糖和不同浓度L-[14C]肉碱（10 - 200 μM）的碳酸氢盐缓冲液灌注心脏。在一些实验中，通过加入0.05 mM汞撒利酸抑制肉碱转运的活性成分。从总转运中减去被动转运，可重建载体介导的L-肉碱转运的饱和曲线。我们的数据表明，在生理肉碱浓度（50 μM）下，机械性超负荷心脏中[14C]肉碱的积累速率显著降低。此外，根据Lineweaver-Burk分析，膜载体对L-肉碱的亲和力显著降低（肉碱的Km为125而不是83 μM，Vmax不变）。上述L-肉碱转运的改变并非由钠的跨膜梯度降低所致，因为肥大心脏的细胞内Na+含量与对照心脏相当。通过在[U-14C]棕榈酸或[1-14C]辛酸存在下获得的14CO2生成量，评估心房灌注的工作心脏氧化外源性游离脂肪酸的能力。如果使用1.2 mM棕榈酸，主动脉-腔静脉瘘大鼠心脏中以每分钟每克干重表示的总14CO2生成量显著降低。另一方面，在存在2.4 mM辛酸（一种绕过肉碱-脂酰肉碱转位酶的底物）的情况下，未检测到14CO2生成量有此类降低。我们的结果表明，L-肉碱转运的减少导致组织肉碱显著降低，可能会损害长链脂肪酸的活化和/或转运到线粒体中。相比之下，短链脂肪酸的氧化直接在线粒体基质中进行，在容量超负荷心脏中不受限制。
