L-leucine transport in rat heart under normal conditions and effects of a simulated hypoxia

L-Leucine plays a central role in the regulation of protein metabolism in h eart and has been implicated in myocardial protection, but little is known about the relationship between these phenomena and leucine transport across the cardiac sarcolemma. In this study we used sarcolemmal vesicles and ven tricular myocytes isolated from rat heart to characterise L-leucine transpo rt under normal conditions and to investigate the effect of simulated hypox ia or inhibition of protein synthesis. The K-m and V-max of leucine uptake were 5.24 +/- 0.65 mM and 1.43 +/- 1.84 nmol min(-1) mg(-1) protein in vesi cles compared to 2.17 +/- 0.13 mM and 1.7 +/- 0.76 nmol min(-1) mul(-1) int racellular space in cells. Transport was not dependent on Na+ or H+ gradien ts. In vesicles L-leucine uptake was increased by trans-stimulation, whilst inhibition was observed with classical system L substrates including 2-ami nobicyclo[2,2,1]-heptane-2-carboxylic acid (BCH) suggesting that this syste m mediated L-leucine transport in heart. L-Leucine uptake into isolated cardiac myocytes was inhibited after 20, 30 and 60 min of simulated hypoxia. This was not caused by reduced cell viabil ity, although the cells underwent a rigor contracture. Inhibition of protei n synthesis did not affect L-leucine transport.