McDermott J C, Bonen A
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Mol Cell Biochem. 1993 May 26;122(2):113-21. doi: 10.1007/BF01076095.
Recent studies have indicated that lactate traversal of the sarcolemmal membrane of skeletal muscle could be a carrier mediated process. In the present study, the initial rates of L(+)-lactate flux (Jlact) were measured in highly purified rat hindlimb skeletal muscle sarcolemmal vesicles. Fluxes were determined by the vesicle uptake of L(+)-[U-14C]lactate from the extra-vesicular medium. Jlact was saturable with respect to increasing concentrations of L(+)-lactate. Regression of these data to the Michaelis-Menten equation yielded a Km of 12.5 mM. Jlact was inhibited 81% by 10 mM pyruvate and 83% by 5mM alpha-cyano 4 hydroxycinnamate (p < 0.05), but not by D-lactate, indicating the presence of a stereoselective monocarboxylate transporter in the sarcolemmal membrane. Preincubation of the vesicles with the protein modifier, N-ethylmaleimide (20mM), inhibited Jlact by 86% (p < 0.05). An inhibitor of the inorganic anion exchanger, SITS (1mM), had no effect on Jlact. However, Jlact was markedly sensitive to an inwardly directed proton gradient (p < 0.05), and the flux was more closely related to the concentration of external ionic L(+)-lactate than to the protonated (HLa) form. These studies suggest that skeletal muscle sarcolemmal membranes possess a specific transport system for L-lactate and other monocarboxylates, which has similar properties to the lactate carrier described for several other tissues.
最近的研究表明，乳酸穿过骨骼肌肌膜的过程可能是一个载体介导的过程。在本研究中，测定了高度纯化的大鼠后肢骨骼肌肌膜囊泡中L(+)-乳酸通量（Jlact）的初始速率。通量通过囊泡从细胞外介质中摄取L(+)-[U-14C]乳酸来确定。Jlact随着L(+)-乳酸浓度的增加而饱和。将这些数据回归到米氏方程得到的Km为12.5 mM。10 mM丙酮酸使Jlact抑制81%，5 mMα-氰基-4-羟基肉桂酸使Jlact抑制83%（p<0.05），但D-乳酸无此作用，表明肌膜中存在立体选择性单羧酸转运体。用蛋白质修饰剂N-乙基马来酰亚胺（20 mM）预孵育囊泡，使Jlact抑制86%（p<0.05）。无机阴离子交换抑制剂SITS（1 mM）对Jlact无影响。然而，Jlact对内向质子梯度明显敏感（p<0.05），且通量与细胞外离子型L(+)-乳酸的浓度比与质子化（HLa）形式的关系更密切。这些研究表明，骨骼肌肌膜具有一种针对L-乳酸和其他单羧酸的特异性转运系统，其性质与其他几种组织中描述的乳酸载体相似。
