Molecular, functional, and genomic characterization of human KCC2, the neuronal K-Cl cotransporter

Luyan Song, Adriana Mercado, Norma Vázquez, Qizhi Xie, Reshma Desai, Alfred L. George, Gerardo Gamba, David B. Mount

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93 Scopus citations


The expression level of the neuronal-specific K-Cl cotransporter KCC2 (SLC12A5) is a major determinant of whether neurons will respond to GABA with a depolarizing, excitatory response or a hyperpolarizing, inhibitory response. In view of the potential role in human neuronal excitability we have characterized the hKCC2 cDNA and gene. The 5.9 kb hKCC2 transcript is specific to brain, and is induced during in vitro differentiation of NT2 teratocarcinoma cells into neuronal NT2-N cells. The 24-exon SLC12A5 gene is on human chromosome 20q13, and contains a polymorphic dinucleotide repeat within intron 1 near a potential binding site for neuron-restrictive silencing factor. Expression of hKCC2 cRNA in Xenopus laevis oocytes results in significant Cl--dependent 86Rb+ uptake under isotonic conditions; cell swelling under hypotonic conditions causes a 20-fold activation, which is blocked by the protein phosphatase inhibitor calyculin-A. In contrast, oocytes expressing mouse KCC4 do not mediate isotonic K-Cl cotransport but express much higher absolute transport activity than KCC2 oocytes under hypotonic conditions. Initial and steady state kinetics of hKCC2-injected oocytes were performed in both isotonic and hypotonic conditions, revealing Kms for K+ and Cl- of 9.3±1.8 mM and 6.8±0.9 mM, respectively; both affinities are significantly higher than KCC1 and KCC4. The Km for Cl- is close to the intracellular Cl- activity of mature neurons, as befits a neuronal efflux mechanism.

Original languageEnglish (US)
Pages (from-to)91-105
Number of pages15
JournalMolecular Brain Research
Issue number1-2
StatePublished - Jun 30 2002


  • GABA

ASJC Scopus subject areas

  • Molecular Biology
  • Cellular and Molecular Neuroscience

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