The low-affinity monocarboxylate transporter MCT4 is adapted to the export of lactate in highly glycolytic cells
The low-affinity monocarboxylate transporter MCT4 is adapted to the export of lactate in highly glycolytic cells
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DOI：
10.1042/0264-6021:3500219
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发表时间：
2000-08-15
影响因子：
4.1
通讯作者：
Bröer, S
中科院分区：
文献类型：
--
作者：
Dimmer, KS;Friedrich, B;Bröer, S
哺乳动物细胞中乳酸盐和其他单羧酸盐的转运由转运蛋白家族介导，称为单羧酸转运蛋白（MCT）。该家族的MCT 4成员最近被鉴定为白色肌细胞的主要同种型，介导乳酸从糖酵解活性肌细胞流出[Wilson，杰克逊，Heddle，Price，Pilegaard，Juel，Bonen，蒙哥马利，Hutter和Halestrap（1998）J.Biol.Chem.273，15920-15926]。为了分析这种转运蛋白的功能特性，大鼠MCT 4在非洲爪蟾卵母细胞中表达，并通过放射性示踪剂的通量测量和使用pH敏感微电极的细胞溶质pH的变化来监测转运活性。与该家族的其他成员相似，通过MCT 4的单羧酸转运伴随着H+跨质膜的转运。乳酸的摄取强烈增加，降低细胞外pH值，这是由于伴随的K-m值下降。MCT 4与其他亚型的区别主要体现在两个方面。首先，MCT 4是一种低亲和力MCT：对于L-乳酸盐，测定的K-m值为17+/-3 mM（pH电极）和34+/-5 mM（L-[U-C-14]乳酸盐通量测量）。其次，乳酸盐是MCT 4的优选底物。其他单羧酸盐的Km值与乳酸盐（丙酮酸盐、2-氧代异己酸盐、2-氧代异戊酸盐、乙酰乙酸盐）的Km值相似，或对转运蛋白（β-羟基丁酸盐和短链脂肪酸）显示出低得多的亲和力。因此，在生理条件下，大鼠MCT将优先转运乳酸盐。α-氰基-4-羟基肉桂酸酯、根皮素和4，4 '-二异硫氰基二苯乙烯-2，2'-二磺酸可竞争性抑制MCT 4转运单羧酸。与MCT 1相似，通过MCT 4的单羧酸转运对巯基试剂对氯汞苯并磺酸的抑制敏感。
Transport of lactate and other monocarboxylates in mammalian cells is mediated by a family of transporters, designated monocarboxylate transporters (MCTs). The MCT4 member of this family has recently been identified as the major isoform of white muscle cells, mediating lactate efflux out of glycolytically active myocytes [Wilson, Jackson, Heddle, Price, Pilegaard, Juel, Bonen, Montgomery, Hutter and Halestrap (1998)J. Biol. Chem. 273, 15920-15926]. To analyse the functional properties of this transporter, rat MCT4 was expressed in Xenopus laevis oocytes and transport activity was monitored by flux measurements with radioactive tracers and by changes of the cytosolic pH using pH-sensitive microelectrodes. Similar to other members of this family, monocarboxylate transport via MCT4 is accompanied by the transport of H+ across the plasma membrane. Uptake of lactate strongly increased with decreasing extracellular pH, which resulted from a concomitant drop in the K-m value. MCT4 could be distinguished from the other isoforms mainly in two respects. First, MCT4 is a low-affinity MCT: for L-lactate K-m values of 17+/-3mM (pH-electrode) and 34+/-5mM (flux measurements with L-[U-C-14]lactate) were determined. Secondly, lactate is the preferred substrate of MCT4. K-m values of other monocarboxylates were either similar to the K-m value for lactate (pyruvate, 2-oxoisohexanoate, 2-oxoisopentanoate, acetoacetate) or displayed much lower affinity for the transporter (beta-hydroxybutyrate and short-chain fatty acids). Under physiological conditions, rat MCT will therefore preferentially transport lactate. Monocarboxylate transport via MCT4 could be competitively inhibited by alpha-cyano-4-hydroxycinnamate, phloretin and partly by 4,4'-di-isothiocyanostilbene- 2,2'-disulphonic acid. Similar to MCT1, monocarboxylate transport via MCT4 was sensitive to inhibition by the thiol reagent p-chloromercuribenzoesulphonic acid.