Vargová L, Chvátal A, Anderová M, Kubinová S, Ziak D, Syková E
Department of Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
J Neurosci Res. 2001 Jul 15;65(2):129-38. doi: 10.1002/jnr.1136.
In rat brain and spinal cord slices, the local extracellular accumulation of K(+), as indicated by K(+) tail currents (I(tail)) after a depolarization step, is greater in the vicinity of oligodendrocytes than that of astrocytes. It has been suggested that this may reflect a smaller extracellular space (ECS) around oligodendrocytes compared to astrocytes [Chvátal et al. [1997] J. Neurosci. Res. 49:98-106; [1999] J. Neurosci. Res. 56:493-505). We therefore compared the effect of osmotic stress in spinal cord slices from 5-11-day-old rats on the changes in reversal potentials (V(rev)) of I(tail) measured by the whole-cell patch-clamp technique and the changes in ECS volume measured by the real-time iontophoretic method. Cell swelling induced by a 20 min perfusion of hypoosmotic solution (200 mmol/kg) decreased the ECS volume fraction from 0.21 +/- 0.01 to 0.15 +/- 0.02, i.e., by 29%. As calculated from V(rev) of I(tail) using the Nernst equation, a depolarizing prepulse increased K(+) around astrocytes from 11.0 to 44.7 mM, i.e., by 306%, and around oligodendrocytes from 26.1 to 54.9 mM, i.e., by 110%. The ECS volume fraction decrease had the same time course as the changes in V(rev) of I(tail). Cell shrinkage in hyperosmotic solution (400 mmol/kg) increased ECS volume fraction from 0.24 +/- 0.02 to 0.32 +/- 0.02, i.e., by 33%. It had no effect on K(+) evoked by a depolarizing prepulse in astrocytes, whereas in oligodendrocytes K(+) rapidly decreased from 52 to 26 mM, i.e., by 50%. The increase in ECS volume was slower than the changes in K(+). These data demonstrate that hypoosmotic solution has a larger effect on the ECS volume around astrocytes than around oligodendrocytes and that hyperosmotic solution affects the ECS volume around oligodendrocytes only. This indicates that increased K(+) accumulation in the vicinity of oligodendrocytes could be due to a restricted ECS. Oligodendrocytes in the CNS are therefore most likely surrounded by clusters of "compacted" ECS, which may selectively affect the diffusion of neuroactive substances in specific areas and directions and facilitate spatial K(+) buffering.
在大鼠脑和脊髓切片中，去极化步骤后由钾离子尾电流（I(tail)）所指示的局部细胞外钾离子（K(+)）积累，在少突胶质细胞附近比星形胶质细胞附近更大。有人提出，这可能反映了与星形胶质细胞相比，少突胶质细胞周围的细胞外空间（ECS）更小[Chvátal等人，[1997]《神经科学研究杂志》49:98 - 106；[1999]《神经科学研究杂志》56:493 - 505）。因此，我们比较了5 - 11日龄大鼠脊髓切片中渗透应激对通过全细胞膜片钳技术测量的I(tail)反转电位（V(rev)）变化以及通过实时离子电泳法测量的ECS体积变化的影响。用低渗溶液（200 mmol/kg）灌注20分钟诱导的细胞肿胀使ECS体积分数从0.21±0.01降至0.15±0.02，即降低了29%。根据能斯特方程从I(tail)的V(rev)计算得出，去极化预脉冲使星形胶质细胞周围的细胞外钾离子浓度（K(+)）从11.0 mM增加到44.7 mM，即增加了306%，而少突胶质细胞周围从26.1 mM增加到54.9 mM，即增加了110%。ECS体积分数的降低与I(tail)的V(rev)变化具有相同的时间进程。在高渗溶液（400 mmol/kg）中细胞收缩使ECS体积分数从0.24±0.02增加到0.32±0.02，即增加了33%。它对去极化预脉冲在星形胶质细胞中诱发的K(+)没有影响，而在少突胶质细胞中K(+)从52 mM迅速降至26 mM，即降低了50%。ECS体积的增加比K(+)的变化更慢。这些数据表明，低渗溶液对星形胶质细胞周围的ECS体积影响比对少突胶质细胞周围的影响更大，而高渗溶液仅影响少突胶质细胞周围的ECS体积。这表明少突胶质细胞附近钾离子积累增加可能是由于ECS受限。因此，中枢神经系统中的少突胶质细胞很可能被“致密化”的ECS簇所包围，这可能选择性地影响神经活性物质在特定区域和方向的扩散，并促进空间钾离子缓冲。
