Calcium diffusion enhanced after cleavage of negatively charged components of brain extracellular matrix by chondroitinase ABC
Calcium diffusion enhanced after cleavage of negatively charged components of brain extracellular matrix by chondroitinase ABC
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DOI：
10.1113/jphysiol.2009.170092
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发表时间：
2009-08-15
影响因子：
5.5
通讯作者：
Nicholson, Charles
中科院分区：
文献类型：
--
作者：
Hrabetova, Sabina;Masri, Daniel;Nicholson, Charles
细胞外钙离子浓度在突触传递和神经元兴奋性以及其他生理过程中起着至关重要的作用。该离子浓度的局部波动的时间过程和程度在很大程度上取决于其有效扩散系数（D*），并且已经推测硫酸软骨素蛋白聚糖（CSPG）和细胞外基质的其他组分上的固定负电荷可能影响钙扩散，因为它是二价阳离子。在这项研究中，我们使用离子选择性微电极结合压力喷射或离子电渗的离子从微量注射器定量扩散特性的新皮层和海马在大鼠脑片。我们表明，D* 钙是小于预测值的一价阳离子四甲基铵（TMA），一种常用的扩散探针的行为，但D* 钙增加后，在两个大脑区域的切片处理软骨素酶ABC，一种酶，主要裂解硫酸软骨素聚糖。这些结果表明，CSPG确实在确定钙在脑组织中的局部扩散特性方面发挥作用，最有可能是通过静电相互作用介导快速平衡结合。相反，软骨素酶ABC不影响TMA扩散或细胞外体积分数，表明该酶不改变细胞外空间的结构，并且在正常脑离子环境中，小的单价阳离子的扩散不受CSPG的影响。众所周知，钙和CSPG在大脑生理学中具有许多不同的作用，包括大脑修复，我们的研究表明它们可能通过钙扩散特性在功能上耦合。
The concentration of extracellular calcium plays a critical role in synaptic transmission and neuronal excitability as well as other physiological processes. The time course and extent of local fluctuations in the concentration of this ion largely depend on its effective diffusion coefficient (D*) and it has been speculated that fixed negative charges on chondroitin sulphate proteoglycans (CSPGs) and other components of the extracellular matrix may influence calcium diffusion because it is a divalent cation. In this study we used ion-selective microelectrodes combined with pressure ejection or iontophoresis of ions from a micropipette to quantify diffusion characteristics of neocortex and hippocampus in rat brain slices. We show that D* for calcium is less than the value predicted from the behaviour of the monovalent cation tetramethylammonium (TMA), a commonly used diffusion probe, but D* for calcium increases in both brain regions after the slices are treated with chondroitinase ABC, an enzyme that predominantly cleaves chondroitin sulphate glycans. These results suggest that CSPGs do play a role in determining the local diffusion properties of calcium in brain tissue, most likely through electrostatic interactions mediating rapid equilibrium binding. In contrast, chondroitinase ABC does not affect either the TMA diffusion or the extracellular volume fraction, indicating that the enzyme does not alter the structure of the extracellular space and that the diffusion of small monovalent cations is not affected by CSPGs in the normal brain ionic milieu. Both calcium and CSPGs are known to have many distinct roles in brain physiology, including brain repair, and our study suggests they may be functionally coupled through calcium diffusion properties.