title: Cl- uptake promoting depolarizing GABA actions in immature rat neocortical neurones is mediated by NKCC1.
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 GABA(A) receptor activation to be depolarizing. The molecular mechanisms underlying this intracellular Cl(-) accumulation remain controversial. Therefore, the GABA reversal potential (E(GABA)) 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 E(GABA) 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.
authors.affiliation: Department of Biological Information Processing, Graduate School of Electronic Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8011, Japan. djyamad@ipc.shizuoka.ac.jp
authors.forename: Junko
authors.initials: J
authors.lastname: Yamada
authors.forename: Akihito
authors.initials: A
authors.lastname: Okabe
authors.forename: Hiroki
authors.initials: H
authors.lastname: Toyoda
authors.forename: Werner
authors.initials: W
authors.lastname: Kilb
authors.forename: Heiko J
authors.initials: HJ
authors.lastname: Luhmann
authors.forename: Atsuo
authors.initials: A
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002712:Chlorides / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D006096:Gramicidin / Q000494:pharmacology; D006706:Homeostasis / Q000502:physiology; D066298:In Vitro Techniques; D019579:Neocortex / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D028021:Sodium-Potassium-Chloride Symporters / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D064466:Solute Carrier Family 12, Member 1; D064506:Solute Carrier Family 12, Member 2; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D005456:Fluorescent Dyes; D012333:RNA, Messenger; D011963:Receptors, GABA-A; C578716:Slc12a1 protein, rat; C578879:Slc12a2 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D064506:Solute Carrier Family 12, Member 2; D006096:Gramicidin; D005680:gamma-Aminobutyric Acid; D016257:Fura-2