Kostić M M, Rosić G L, Segal M B, Rosić M A
Institute of Physiology, Faculty of Medicine, University of Kragujevac, Yugoslavia.
Exp Physiol. 1995 Nov;80(6):969-79. doi: 10.1113/expphysiol.1995.sp003908.
L-Arginine is the physiological substrate for the formation of nitric oxide (NO) and accounts for the biological activity of endothelium-derived relaxing factor. We have studied L-arginine transport in the heart using a rapid dual-isotope dilution technique. The time course of L-[3H]arginine uptake (extraction) by the isolated perfused guinea-pig heart was found to occur in two phases. The first phase reached a plateau in 6.6 +/- 0.6 s and lasted 8.8 +/- 0.7 s, whereas the second phase developed a plateau after 16.3 +/- 0.8 s. The first phase of maximal uptake (Umax,1) accounted for 13.4 +/- 1.4% of the total uptake and the second (Umax,2) for 32.3 +/- 1.8%. The two phases of uptake were inhibited by unlabelled L-arginine in a dose-dependent manner, which suggests that both phases are carrier mediated. The degree of inhibition of Umax,1 and Umax,2 by unlabelled L-arginine was not significantly different. Studies of the kinetics of uptake of these processes revealed an apparent Km,1 of 183 +/- 10 microM with a Vmax,1 of 50 +/- 10 nmol min-1 g-1 for the first phase and Km,2 of 167 +/- 14 microM with a Vmax,2 of 93 +/- 13 nmol min-1 g-1 for the second phase of uptake. These results suggest a similar affinity for the receptors of both transport systems, but with different values for Vmax (P < 0.05). In contrast, 1 mM unlabelled D-arginine had no effect on either the first or second phase of uptake of L-[3H]arginine by the heart, which suggests that these processes are stereospecific. In the presence of the L-stereoisomer of nitro-arginine-mono-methyl ester (L-NAME), a potent inhibitor of NO synthesis, the Umax,1 was inhibited by about 60% while Umax,2 was inhibited by only 20%, which suggests that there is a difference in the effect of L-NAME on the two phases of L-arginine uptake. The first phase most probably represents uptake into the capillary wall, i.e. endothelium and smooth muscle, while the second phase represents entry into the extra-endothelial compartment, i.e. the cardiac myocytes and fibroblasts.
L-精氨酸是一氧化氮（NO）形成的生理底物，也是内皮源性舒张因子生物活性的物质基础。我们采用快速双同位素稀释技术研究了心脏中L-精氨酸的转运情况。发现离体灌注豚鼠心脏对L-[³H]精氨酸的摄取（提取）时间进程分为两个阶段。第一阶段在6.6±0.6秒达到平台期，并持续8.8±0.7秒，而第二阶段在16.3±0.8秒后出现平台期。最大摄取量的第一阶段（Umax,1）占总摄取量的13.4±1.4%，第二阶段（Umax,2）占32.3±1.8%。两个摄取阶段均受到未标记L-精氨酸的剂量依赖性抑制，这表明两个阶段均由载体介导。未标记L-精氨酸对Umax,1和Umax,2的抑制程度无显著差异。对这些过程摄取动力学的研究表明，第一阶段的表观Km,1为183±10μM，Vmax,1为50±10 nmol·min⁻¹·g⁻¹，第二阶段摄取的Km,2为167±14μM，Vmax,2为93±13 nmol·min⁻¹·g⁻¹。这些结果表明，两种转运系统对受体的亲和力相似，但Vmax值不同（P<0.05）。相比之下，1 mM未标记的D-精氨酸对心脏摄取L-[³H]精氨酸的第一阶段或第二阶段均无影响，这表明这些过程具有立体特异性。在一氧化氮合成的强效抑制剂硝基精氨酸甲酯的L-立体异构体（L-NAME）存在的情况下，Umax,1被抑制约60%，而Umax,2仅被抑制20%，这表明L-NAME对L-精氨酸摄取的两个阶段的作用存在差异。第一阶段很可能代表摄取进入毛细血管壁，即内皮和平滑肌，而第二阶段代表进入内皮外间隙，即心肌细胞和成纤维细胞。
