Clayton G H, Owens G C, Wolff J S, Smith R L
Neurology and Pediatrics, Department of Neurology, B-182, University of Colorado Health Sciences Center, 4200 E. Ninth Ave., Denver, CO 80262, USA.
Brain Res Dev Brain Res. 1998 Aug 8;109(2):281-92. doi: 10.1016/s0165-3806(98)00078-9.
Neuronal precursors and immature cortical neurons actively accumulate Cl- and as a consequence depolarize in response to GABAA receptor activation. With maturity, intracellular Cl- decreases resulting in a shift towards GABAA inhibition. These observations suggest that changes in expression of cation-Cl- cotransporters may have a significant role in the ontogeny of neuronal Cl- homeostasis. Using ribonuclease protection analysis and in situ hybridization we examined the developmental expression of all presently known members of the cation-Cl- cotransporter gene family in rat brain. Of the inwardly directed cotransporters, NKCC-1, NKCC-2, and NCC-1, only NKCC-1 was detected at significant levels in brain. NKCC-1 was expressed in neurons, appearing first in cortical plate but not in ventricular or subventricular zone. Expression levels peaked by the third postnatal week and were maintained into adulthood. The outwardly directed cotransporters, KCC-1 and KCC-2, demonstrated significantly different levels and time courses of expression. KCC-1 was expressed prenatally at very low levels which increased little over the course of development. In contrast, KCC-2 expression appeared perinatally and increased dramatically after the first week of postnatal life. Differential changes in expression of this gene family occurred during periods of critical shifts in chloride homeostasis and GABA response suggestive of a role in these processes. Furthermore the absence of expression of known inwardly directed cotransporters in Cl- accumulating neuroepithelia and lack of evidence for glial expression suggests that as yet unidentified members of this gene family may be involved in chloride homeostasis in immature neuronal precursors and neuroglia.
神经元前体和未成熟的皮质神经元会主动积累氯离子，因此在γ-氨基丁酸A型（GABAA）受体激活时会发生去极化。随着神经元成熟，细胞内氯离子减少，导致向GABAA介导的抑制作用转变。这些观察结果表明，阳离子-氯离子共转运体表达的变化可能在神经元氯离子稳态的个体发生中起重要作用。我们使用核糖核酸酶保护分析和原位杂交技术，研究了阳离子-氯离子共转运体基因家族目前已知所有成员在大鼠脑中的发育表达情况。在内向型共转运体NKCC-1、NKCC-2和NCC-1中，只有NKCC-1在脑中被检测到显著水平。NKCC-1在神经元中表达，最早出现在皮质板，但在脑室或脑室下区未出现。表达水平在出生后第三周达到峰值，并维持到成年期。外向型共转运体KCC-1和KCC-2表现出显著不同的表达水平和时间进程。KCC-1在产前以非常低的水平表达，在发育过程中几乎没有增加。相比之下，KCC-2的表达在围产期出现，并在出生后第一周后急剧增加。该基因家族表达的差异变化发生在氯离子稳态和GABA反应的关键转变期，提示其在这些过程中发挥作用。此外，在积累氯离子的神经上皮中未检测到已知内向型共转运体的表达，且缺乏胶质细胞表达的证据，这表明该基因家族中尚未鉴定的成员可能参与未成熟神经元前体和神经胶质细胞的氯离子稳态。
