Alonso de la Torre S R, Serrano M A, Alvarado F, Medina J M
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Salamanca, Spain.
Biochem J. 1991 Sep 1;278 ( Pt 2)(Pt 2):535-41. doi: 10.1042/bj2780535.
The mechanism for L-lactate transport across microvillous membrane vesicles prepared from rat placenta was examined. Uptake of L-lactate into these vesicles was mainly the result of transport into the intravesicular (osmotically active) space. The initial rate of L-lactate uptake was not affected by the presence of an inward gradient of either Na+ or K+. In the presence of an inward-directed proton gradient, L-lactate uptake was markedly stimulated, accumulating at concentrations 6-7-fold higher than the equilibrium. Lower transmembrane pH gradients were associated with slower initial uptakes and smaller overshoots. L-Lactate uptake determined under an inside-directed pH gradient was strongly inhibited by p-chloromercuriphenylsulphonic acid, a protein-thiol oxidizing agent. L-Lactate uptake was: (1) saturable as a function of the concentration of L-lactate, (2) inhibited by monocarboxylic acids such as pyruvate, D-lactate, beta-hydroxybutyrate and alpha-cyano-4-hydroxycinnamic acid, and (3) temperature-dependent. When present inside the vesicles, L-lactate, pyruvate and beta-hydroxybutyrate caused trans-stimulation of L-lactate uptake both in the presence and in the absence of an inside-directed pH gradient, indicating that L-lactate transport is a reversible process that can be shared by other monocarboxylic acids. There were no significant changes in maximal initial rate or in the kinetic parameters of L-lactate transport during the last 3 days of gestation.
研究了L-乳酸跨大鼠胎盘制备的微绒毛膜囊泡转运的机制。L-乳酸进入这些囊泡主要是转运到囊泡内（具有渗透活性）空间的结果。L-乳酸摄取的初始速率不受Na+或K+内向梯度存在的影响。在存在内向质子梯度的情况下，L-乳酸摄取受到显著刺激，积累浓度比平衡浓度高6-7倍。较低的跨膜pH梯度与较慢的初始摄取和较小的超调相关。在内向pH梯度下测定的L-乳酸摄取受到对氯汞苯磺酸（一种蛋白质-硫醇氧化剂）的强烈抑制。L-乳酸摄取具有以下特点：（1）作为L-乳酸浓度的函数呈饱和状态，（2）受到单羧酸如丙酮酸、D-乳酸、β-羟基丁酸和α-氰基-4-羟基肉桂酸的抑制，（3）依赖温度。当存在于囊泡内部时，L-乳酸、丙酮酸和β-羟基丁酸在存在和不存在内向pH梯度的情况下均引起L-乳酸摄取的反式刺激，表明L-乳酸转运是一个可逆过程，可被其他单羧酸共享。在妊娠的最后3天，L-乳酸转运的最大初始速率或动力学参数没有显著变化。
