Wang Y, Wright P M, Heigenhauser G J, Wood C M
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
Am J Physiol. 1997 May;272(5 Pt 2):R1577-87. doi: 10.1152/ajpregu.1997.272.5.R1577.
This study used an isolated-perfused tail-trunk preparation of rainbow trout to examine the uptake and release of lactate (Lac) and metabolic protons (delta H+M) in resting and exercised fish white muscle. In exercised muscle, L(+)-Lac efflux was inhibited (approximately 40%) by 5 mM alpha-cyano-4-hydroxycinnamate (CIN), but not by 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) or 0.1 mM amiloride. These results suggest that Lac release occurs through a Lac(-)-H- symport and the free diffusion of lactic acid (HLac) or Lac-, but not via the Lac-/HCO3(-)-Cl- antiporter. Lac efflux was accompanied by delta H+m influx in all treatments, and increased delta H+m influx occurred after SITS treatment. In resting muscle, Lac uptake rates were greater than Lac efflux rates in the postexercise preparation. L-Lac influx exhibited partial saturation kinetics, whereas D(-)-Lac influx was linearly related to its extracellular concentration (0-32 mM). At 16 mM extracellular L-Lac, with a negligible transmembrane L-HLac gradient and an outwardly directed not driving force on L-Lac-, CIN, and SITS reduced net L-Lac uptake by 75 and 45%, respectively. At 16 mM extracellular concentration, D-Lac influx was 64% of the net L-Lac influx. These results suggest that in trout muscle at 16 mM extracellular L-Lac, the Lac -H+ symport accounts for 30-36%, the Lac-/HCO3(-)-Cl- antiport for 39-45%, and diffusion for 19-25% of uptake, although the latter is probably overestimated and the former underestimated for methodological reasons. Net L-Lac efflux was not affected by extracellular D-Lac concentration and/or D-Lac influx, implying the existence of a concurrent L-Lac efflux during L-Lac influx. The D-Lac influx kinetics data indicated that the Lac-/HCO3 antiport was not saturable in the extracellular D-Lac concentration range of 0-32 mM. This study clearly demonstrates the involvement of carrier-mediated transport in transmembrane Lac movement in fish muscle and supports the "active lactate retention" mechanism proposed by Turner and Wood (J. Exp. Biol. 105: 895-401, 1983).
本研究采用虹鳟鱼离体灌注尾干制备法，研究静息和运动状态下鱼白肌中乳酸（Lac）和代谢质子（δH⁺M）的摄取与释放。在运动肌肉中，5 mM α-氰基-4-羟基肉桂酸（CIN）可抑制L(+)-Lac外流（约40%），但0.5 mM 4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS）或0.1 mM氨氯吡咪则无此作用。这些结果表明，Lac释放是通过Lac⁻-H⁺同向转运以及乳酸（HLac）或Lac⁻的自由扩散发生的，而非通过Lac⁻/HCO₃⁻-Cl⁻反向转运体。在所有处理中，Lac外流均伴有δH⁺m内流，且SITS处理后δH⁺m内流增加。在静息肌肉中，运动后制备物中Lac摄取率大于Lac外流率。L-Lac内流呈现部分饱和动力学，而D(-)-Lac内流与其细胞外浓度（0 - 32 mM）呈线性关系。在细胞外L-Lac浓度为16 mM时，跨膜L-HLac梯度可忽略不计，且对L-Lac⁻、CIN和SITS不存在外向驱动力，此时CIN和SITS分别使L-Lac净摄取减少75%和45%。在细胞外浓度为16 mM时，D-Lac内流为L-Lac净内流的64%。这些结果表明，在细胞外L-Lac浓度为16 mM时，虹鳟鱼肌肉中Lac -H⁺同向转运占摄取的30 - 36%，Lac⁻/HCO₃⁻-Cl⁻反向转运占39 - 45%，扩散占19 - 25%，不过由于方法学原因，后者可能被高估，前者可能被低估。L-Lac净外流不受细胞外D-Lac浓度和/或D-Lac内流的影响，这意味着在L-Lac内流过程中存在同时发生的L-Lac外流。D-Lac内流动力学数据表明，在细胞外D-Lac浓度范围为0 - 32 mM时，Lac⁻/HCO₃⁻反向转运不饱和。本研究清楚地证明了载体介导的转运参与了鱼肌肉中跨膜Lac的移动，并支持了Turner和Wood（《实验生物学杂志》105: 895 - 401, 1983）提出的“主动乳酸保留”机制。
