title: Molecular, functional, and genomic characterization of human KCC2, the neuronal K-Cl cotransporter.
abstract: 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 (86)Rb(+) 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 K(m)s 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 K(m) for Cl(-) is close to the intracellular Cl(-) activity of mature neurons, as befits a neuronal efflux mechanism.
authors.affiliation: Department of Medicine, Nashville VA Medical Center and Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors.forename: Luyan
authors.initials: L
authors.lastname: Song
authors.forename: Adriana
authors.initials: A
authors.lastname: Mercado
authors.forename: Norma
authors.initials: N
authors.lastname: Vázquez
authors.forename: Qizhi
authors.initials: Q
authors.lastname: Xie
authors.forename: Reshma
authors.initials: R
authors.lastname: Desai
authors.forename: Alfred L
authors.initials: AL
authors.lastname: George
authors.forename: Gerardo
authors.initials: G
authors.lastname: Gamba
authors.forename: David B
authors.initials: DB
authors.lastname: Mount
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D005091:Exons; D015870:Gene Expression; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology; D007438:Introns; D007552:Isotonic Solutions / Q000494:pharmacology; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D009865:Oocytes / Q000502:physiology; D011110:Polymorphism, Genetic; D012414:Rubidium Radioisotopes; D027981:Symporters / Q000235:genetics* / Q000378:metabolism*; D014471:Umbilical Veins / Q000166:cytology; D014982:Xenopus laevis; D000096922:K Cl- Cotransporters
chemical_list: D007038:Hypotonic Solutions; D007552:Isotonic Solutions; D012414:Rubidium Radioisotopes; D027981:Symporters; D000096922:K Cl- Cotransporters