Larsen Brian Roland, Assentoft Mette, Cotrina Maria L, Hua Susan Z, Nedergaard Maiken, Kaila Kai, Voipio Juha, MacAulay Nanna
Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
Glia. 2014 Apr;62(4):608-22. doi: 10.1002/glia.22629. Epub 2014 Jan 30.
Network activity in the brain is associated with a transient increase in extracellular K(+) concentration. The excess K(+) is removed from the extracellular space by mechanisms proposed to involve Kir4.1-mediated spatial buffering, the Na(+)/K(+)/2Cl(-) cotransporter 1 (NKCC1), and/or Na(+)/K(+)-ATPase activity. Their individual contribution to [K(+)]o management has been of extended controversy. This study aimed, by several complementary approaches, to delineate the transport characteristics of Kir4.1, NKCC1, and Na(+)/K(+)-ATPase and to resolve their involvement in clearance of extracellular K(+) transients. Primary cultures of rat astrocytes displayed robust NKCC1 activity with [K(+)]o increases above basal levels. Increased [K(+)]o produced NKCC1-mediated swelling of cultured astrocytes and NKCC1 could thereby potentially act as a mechanism of K(+) clearance while concomitantly mediate the associated shrinkage of the extracellular space. In rat hippocampal slices, inhibition of NKCC1 failed to affect the rate of K(+) removal from the extracellular space while Kir4.1 enacted its spatial buffering only during a local [K(+)]o increase. In contrast, inhibition of the different isoforms of Na(+)/K(+)-ATPase reduced post-stimulus clearance of K(+) transients. The astrocyte-characteristic α2β2 subunit composition of Na(+)/K(+)-ATPase, when expressed in Xenopus oocytes, displayed a K(+) affinity and voltage-sensitivity that would render this subunit composition specifically geared for controlling [K(+)]o during neuronal activity. In rat hippocampal slices, simultaneous measurements of the extracellular space volume revealed that neither Kir4.1, NKCC1, nor Na(+)/K(+)-ATPase accounted for the stimulus-induced shrinkage of the extracellular space. Thus, NKCC1 plays no role in activity-induced extracellular K(+) recovery in native hippocampal tissue while Kir4.1 and Na(+)/K(+)-ATPase serve temporally distinct roles.
大脑中的网络活动与细胞外K(+)浓度的短暂升高有关。多余的K(+)通过涉及Kir4.1介导的空间缓冲、Na(+)/K(+)/2Cl(-)共转运体1（NKCC1）和/或Na(+)/K(+)-ATP酶活性的机制从细胞外空间被清除。它们对[K(+)]o管理的各自贡献一直存在广泛争议。本研究旨在通过几种互补方法来描述Kir4.1、NKCC1和Na(+)/K(+)-ATP酶的转运特性，并解决它们在清除细胞外K(+)瞬变中的作用。大鼠星形胶质细胞的原代培养显示出强大的NKCC1活性，[K(+)]o高于基础水平时会增加。[K(+)]o升高导致NKCC1介导培养的星形胶质细胞肿胀，因此NKCC1可能作为K(+)清除的一种机制，同时介导细胞外空间的相关收缩。在大鼠海马切片中，抑制NKCC1未能影响K(+)从细胞外空间的清除速率，而Kir4.1仅在局部[K(+)]o升高时发挥其空间缓冲作用。相反，抑制Na(+)/K(+)-ATP酶的不同同工型会降低刺激后K(+)瞬变的清除。当在非洲爪蟾卵母细胞中表达时，星形胶质细胞特有的Na(+)/K(+)-ATP酶α2β2亚基组成表现出K(+)亲和力和电压敏感性，这将使该亚基组成特别适合在神经元活动期间控制[K(+)]o。在大鼠海马切片中，对细胞外空间体积的同步测量表明，Kir4.1、NKCC1和Na(+)/K(+)-ATP酶均不能解释刺激引起的细胞外空间收缩。因此，NKCC1在天然海马组织中对活动诱导的细胞外K(+)恢复不起作用，而Kir4.1和Na(+)/K(+)-ATP酶发挥不同的时间作用。
