Clearance of extracellular K+ during muscle contraction--roles of membrane transport and diffusion.
Clearance of extracellular K+ during muscle contraction--roles of membrane transport and diffusion.
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DOI：
10.1085/jgp.200809971
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发表时间：
2008-05
影响因子：
3.8
通讯作者：
Clausen, Torben
中科院分区：
文献类型：
--
作者：
Clausen, Torben
肌肉的兴奋通常导致细胞K+的净损失和细胞外K+（[ K+ ]o）的上升，这反过来抑制兴奋性和收缩性。因此，重要的是要确定K+是如何通过扩散到周围环境中或通过再积累到肌肉细胞中而被清除的。[K+ ]o升高的抑制作用可从离体肌肉中强直力变化的时程进行评估，其中通过去除孵育介质并使肌肉在空气中收缩来消除K+的扩散清除。强直的力量，耐力，和力恢复的测量结果表明，在大鼠比目鱼肌和趾长伸肌（EDL）的肌肉收缩在缓冲液中或在空气中长达8分钟的性能之间没有显着差异。哇巴因诱导的抑制K+清除通过Na+，K+泵显着降低收缩耐力和力恢复在空气中。在含有10 mM K+的缓冲液中孵育明显抑制了力的发展和耐力，并且通过用β2-激动剂沙丁胺醇刺激Na+、K+泵，这些作用显著降低。在60 Hz下连续刺激30-60 s后，从洗脱实验评估释放到细胞外间隙中的K+的量。EDL每次脉冲释放的细胞内K+是比目鱼肌的四倍，并且在两块肌肉中，平均[K+ ]o分别达到52.4和26.0 mM，明显高于之前检测到的。总之，防止K+从离体工作肌的细胞外空间扩散仅对收缩性能产生适度干扰。Na+、K+泵在K+的清除和力的维持中起主要作用。这一新的信息对于评估肌肉中K+诱导的抑制作用非常重要，其中K+的扩散清除率因张力发展而降低，足以抑制循环。
Excitation of muscle often leads to a net loss of cellular K+ and a rise in extracellular K+ ([ K+ ]o), which in turn inhibits excitability and contractility. It is important, therefore, to determine how this K+ is cleared by diffusion into the surroundings or by reaccumulation into the muscle cells. The inhibitory effects of the rise in [K+ ]o may be assessed from the time course of changes in tetanic force in isolated muscles where diffusional clearance of K+ is eliminated by removing the incubation medium and allowing the muscles to contract in air. Measurements of tetanic force, endurance, and force recovery showed that in rat soleus and extensor digitorum longus (EDL) muscles there was no significant difference between the performance of muscles contracting in buffer or in air for up to 8 min. Ouabain-induced inhibition of K+ clearance via the Na+,K+ pumps markedly reduced contractile endurance and force recovery in air. Incubation in buffer containing 10 mM K+ clearly inhibited force development and endurance, and these effects were considerably reduced by stimulating Na+,K+ pumps with the β2-agonist salbutamol. Following 30–60 s of continuous stimulation at 60 Hz, the amount of K+ released into the extracellular space was assessed from washout experiments. The release of intracellular K+ per pulse was fourfold larger in EDL than in soleus, and in the two muscles, the average [K+ ]o reached 52.4 and 26.0 mM, respectively, appreciably higher than previously detected. In conclusion, prevention of diffusion of K+ from the extracellular space of isolated working muscles causes only modest interference with contractile performance. The Na+,K+ pumps play a major role in the clearance of K+ and the maintenance of force. This new information is important for the evaluation of K+-induced inhibition in muscles, where diffusional clearance of K+ is reduced by tension development sufficient to suppress circulation.
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