Cl uptake promoting depolarizing GABA actions in immature rat neocortical neurones is mediated by NKCC1

Authors

  • Junko Yamada,

    1. Department of Biological Information Processing, Graduate School of Electronic Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8011, Japan
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  • Akihito Okabe,

    1. Department of Physiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan
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  • Hiroki Toyoda,

    1. Department of Physiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan
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  • Werner Kilb,

    1. Institute of Physiology and Pathophysiology, Johannes Gutenberg-University, D-55099 Mainz, Germany
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  • Heiko J. Luhmann,

    1. Institute of Physiology and Pathophysiology, Johannes Gutenberg-University, D-55099 Mainz, Germany
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  • Atsuo Fukuda

    1. Department of Biological Information Processing, Graduate School of Electronic Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8011, Japan
    2. Department of Physiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan
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  • J. Yamada and A. Okabe contributed equally to this work.

Corresponding author J. Yamada: Department of Biological Information Processing, Graduate School of Electronic Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8011, Japan. Email: djyamad@ipc.shizuoka.ac.jp

Abstract

GABA is the principal inhibitory neurotransmitter in the mature brain, but during early postnatal development the elevated [Cl]i in immature neocortical neurones causes GABAA receptor activation to be depolarizing. The molecular mechanisms underlying this intracellular Cl accumulation remain controversial. Therefore, the GABA reversal potential (EGABA) or [Cl]i in early postnatal rat neocortical neurones was measured by the gramicidin-perforated patch-clamp method, and the relative expression levels of the cation−Cl cotransporter mRNAs (in the same cells) were examined by semiquantitative single-cell multiplex RT-PCR to look for statistical correlations with [Cl]i. The mRNA expression levels were positively (the Cl accumulating Na+,K+−2Cl cotransporter NKCC1) or negatively (the Cl extruding K+−Cl cotransporter KCC2) correlated with [Cl]i. NKCC1 mRNA expression was high in early postnatal days, but decreased during postnatal development, whereas KCC2 mRNA expression displayed the opposite pattern. [Cl]i and NKCC1 mRNA expression were each higher in cortical plate (CP) neurones than in the presumably older layer V/VI pyramidal neurones in a given slice. The pharmacological effects of bumetanide on EGABA were consistent with the different expression levels of NKCC1 mRNA. These data suggest that NKCC1 may play a pivotal role in the generation of GABA-mediated depolarization in immature CP cells, while KCC2 promotes the later maturation of GABAergic inhibition in the rat neocortex.

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