title: Potassium-coupled chloride cotransport controls intracellular chloride in rat neocortical pyramidal neurons.
abstract: Chloride (Cl(-)) homeostasis is critical for many cell functions including cell signaling and volume regulation. The action of GABA at GABA(A) receptors is primarily determined by the concentration of intracellular Cl(-). Developmental regulation of intracellular Cl(-) results in a depolarizing response to GABA in immature neocortical neurons and a hyperpolarizing or shunting response in mature neocortical neurons. One protein that participates in Cl(-) homeostasis is the neuron-specific K(+)-Cl(-) cotransporter (KCC2). Thermodynamic considerations predict that in the physiological ranges of intracellular Cl(-) and extracellular K(+) concentrations, KCC2 can act to either extrude or accumulate Cl(-). To test this hypothesis, we examined KCC2 function in pyramidal cells from rat neocortical slices in mature (18-28 d postnatal) and immature (3-6 d postnatal) rats. Intracellular Cl(-) concentration was estimated from the reversal potential of whole-cell currents evoked by local application of exogenous GABA. Both increasing and decreasing the extracellular K(+) concentration resulted in a concomitant change in intracellular Cl(-) concentration in neurons from mature rats. KCC2 inhibition by furosemide caused a change in the intracellular Cl(-) concentration that depended on the concentration of pipette Cl(-); in recordings with low pipette Cl(-), furosemide lowered intracellular Cl(-), whereas in recordings with elevated pipette Cl(-), furosemide raised intracellular Cl(-). In neurons from neonatal rats, manipulation of extracellular K(+) had no effect on intracellular Cl(-) concentration, consistent with the minimal KCC2 mRNA levels observed in neocortical neurons from immature animals. These data demonstrate a physiologically relevant and developmentally regulated role for KCC2 in Cl(-) homeostasis via both Cl(-) extrusion and accumulation.
authors.affiliation: Department of Neurobiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: DeFazio
authors.forename: S
authors.initials: S
authors.lastname: Keros
authors.forename: M W
authors.initials: MW
authors.lastname: Quick
authors.forename: J J
authors.initials: JJ
authors.lastname: Hablitz
mesh_terms: D000375:Aging / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism* / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects; D005665:Furosemide / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects; D019579:Neocortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D017966:Pyramidal Cells / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027981:Symporters; D013816:Thermodynamics; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology; D000096922:K Cl- Cotransporters
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D004232:Diuretics; D005665:Furosemide; D011188:Potassium; D012333:RNA, Messenger; D027981:Symporters; D005680:gamma-Aminobutyric Acid; D000096922:K Cl- Cotransporters