Cl- uptake promoting depolarizing GABA actions in immature rat neocortical neurones is mediated by NKCC1.
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.
Yamada
Junko
J
Department of Biological Information Processing, Graduate School of Electronic Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8011, Japan. djyamad@ipc.shizuoka.ac.jp
Okabe
Akihito
A
Toyoda
Hiroki
H
Kilb
Werner
W
Luhmann
Heiko J
HJ
Fukuda
Atsuo
A
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*
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