RGD Reference Report - Cation transport by the neuronal K(+)-Cl(-) cotransporter KCC2: thermodynamics and kinetics of alternate transport modes. - Rat Genome Database

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Cation transport by the neuronal K(+)-Cl(-) cotransporter KCC2: thermodynamics and kinetics of alternate transport modes.

Authors: Williams, JR  Payne, JA 
Citation: Williams JR and Payne JA, Am J Physiol Cell Physiol. 2004 Oct;287(4):C919-31. Epub 2004 Jun 2.
RGD ID: 2303821
Pubmed: PMID:15175220   (View Abstract at PubMed)
DOI: DOI:10.1152/ajpcell.00005.2004   (Journal Full-text)

Both Cs(+) and NH(4)(+) alter neuronal Cl(-) homeostasis, yet the mechanisms have not been clearly elucidated. We hypothesized that these two cations altered the operation of the neuronal K(+)-Cl(-) cotransporter (KCC2). Using exogenously expressed KCC2 protein, we first examined the interaction of cations at the transport site of KCC2 by monitoring furosemide-sensitive (86)Rb(+) influx as a function of external Rb(+) concentration at different fixed external cation concentrations (Na(+), Li(+), K(+), Cs(+), and NH(4)(+)). Neither Na(+) nor Li(+) affected furosemide-sensitive (86)Rb(+) influx, indicating their inability to interact at the cation translocation site of KCC2. As expected for an enzyme that accepts Rb(+) and K(+) as alternate substrates, K(+) was a competitive inhibitor of Rb(+) transport by KCC2. Like K(+), both Cs(+) and NH(4)(+) behaved as competitive inhibitors of Rb(+) transport by KCC2, indicating their potential as transport substrates. Using ion chromatography to measure unidirectional Rb(+) and Cs(+) influxes, we determined that although KCC2 was capable of transporting Cs(+), it did so with a lower apparent affinity and maximal velocity compared with Rb(+). To assess NH(4)(+) transport by KCC2, we monitored intracellular pH (pH(i)) with a pH-sensitive fluorescent dye after an NH(4)(+)-induced alkaline load. Cells expressing KCC2 protein recovered pH(i) much more rapidly than untransfected cells, indicating that KCC2 can mediate net NH(4)(+) uptake. Consistent with KCC2-mediated NH(4)(+) transport, pH(i) recovery in KCC2-expressing cells could be inhibited by furosemide (200 microM) or removal of external [Cl(-)]. Thermodynamic and kinetic considerations of KCC2 operating in alternate transport modes can explain altered neuronal Cl(-) homeostasis in the presence of Cs(+) and NH(4)(+).

Gene Ontology Annotations    Click to see Annotation Detail View

Biological Process
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
ammonium transmembrane transport  IDA 2303821 RGD 
chloride transport  IDA 2303821 RGD 
potassium ion transport  IDA 2303821 RGD 

Molecular Function
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
ammonium transmembrane transporter activity  IDA 2303821 RGD 
potassium:chloride symporter activity  IDA 2303821 RGD 

Objects Annotated

Genes (Rattus norvegicus)
Slc12a5  (solute carrier family 12 member 5)


Additional Information