Juel C
Copenbagen Muscle Research Centre, August Krogb Institute, Denmark.
Acta Physiol Scand. 1996 Mar;156(3):369-74. doi: 10.1046/j.1365-201X.1996.206000.x.
In skeletal muscle, intracellular pH is more alkaline than would be predicted if H+ were passively distributed across the sarcolemma. Therefore, the passive influx of H+ must be counteracted by transport processes mediating H+ afflux. In resting skeletal muscle, these transport processes are Na+/H+ exchange and bicarbonate-dependent systems. During periods of high energy demand, skeletal muscle produces large amounts of lactic acid. The internal accumulation of lactic acid reduces pH, which may cause fatigue. It is therefore important for muscle cells to be able to regulate pH during and after activity. A part of the accumulated lactate and H+ is metabolized, but a considerable fraction is released from the cell. The efflux of H+ and lactate might be mediated by the lactate/proton co-transport system found in almost all cell types in the body. The role of lactate/proton co-transport in pH regulation has been studied both with intact cells and with sarcolemmal vesicles. In intact cells, inhibitors of lactate/proton transport have been shown to accelerate the development of fatigue, and to delay the recovery after activity. A comparison with vesicles has demonstrated that, at low pH, and with a high lactate concentration, the capacity for H+ removal is higher via the lactate/proton co-transport system than via the sum of the Na+/H+ exchange and bicarbonate-dependent exchange systems. Therefore, the carrier-mediated lactate/proton efflux is of major importance for pH regulation in connection with muscle activity. The lactate/proton transport system has been shown to undergo long-term changes depending on the level of physical activity. The capacity of the system was enhanced after intense training or chronic stimulation, and reduced after denervation. It is concluded that the lactate/proton transport system is of major importance for pH regulation in skeletal muscle, and that changes in the amount of transporters are one of the many adaptations to physical activity.
在骨骼肌中，细胞内pH值比假设H⁺被动分布于肌膜两侧时所预测的更偏碱性。因此，H⁺的被动内流必须被介导H⁺外流的转运过程所抵消。在静息骨骼肌中，这些转运过程是Na⁺/H⁺交换和碳酸氢盐依赖系统。在能量需求高的时期，骨骼肌会产生大量乳酸。乳酸在细胞内积累会降低pH值，这可能导致疲劳。因此，肌肉细胞在活动期间及活动后能够调节pH值非常重要。一部分积累的乳酸和H⁺会被代谢，但相当一部分会从细胞中释放出来。H⁺和乳酸的外流可能由几乎存在于身体所有细胞类型中的乳酸/质子共转运系统介导。乳酸/质子共转运在pH调节中的作用已在完整细胞和肌膜囊泡中进行了研究。在完整细胞中，乳酸/质子转运抑制剂已被证明会加速疲劳的发展，并延迟活动后的恢复。与囊泡的比较表明，在低pH值和高乳酸浓度下，通过乳酸/质子共转运系统去除H⁺的能力高于通过Na⁺/H⁺交换和碳酸氢盐依赖交换系统的总和。因此，载体介导的乳酸/质子外流对于与肌肉活动相关的pH调节至关重要。乳酸/质子转运系统已被证明会根据身体活动水平发生长期变化。经过高强度训练或慢性刺激后，该系统的能力增强，而去神经支配后则降低。结论是，乳酸/质子转运系统对于骨骼肌的pH调节至关重要，并且转运体数量的变化是对身体活动的众多适应性之一。
