Article

Variable loss of Kir4.1 channel function in SeSAME syndrome mutations

Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455,USA.
Biochemical and Biophysical Research Communications (Impact Factor: 2.28). 09/2010; 399(4):537-41. DOI: 10.1016/j.bbrc.2010.07.105
Source: PubMed

ABSTRACT SeSAME syndrome is a complex disease characterized by seizures, sensorineural deafness, ataxia, mental retardation and electrolyte imbalance. Mutations in the inwardly rectifying potassium channel Kir4.1 (KCNJ10 gene) have been linked to this condition. Kir4.1 channels are weakly rectifying channels expressed in glia, kidney, cochlea and possibly other tissues. We determined the electrophysiological properties of SeSAME mutant channels after expression in transfected mammalian cells. We found that a majority of mutations (R297C, C140R, R199X, T164I) resulted in complete loss of Kir4.1 channel function while two mutations (R65P and A167V) produced partial loss of function. All mutant channels were rescued upon co-transfection of wild-type Kir4.1 but not Kir5.1 channels. Cell-surface biotinylation assays indicate significant plasma membrane expression of all mutant channels with exception of the non-sense mutant R199X. These results indicate the differential loss of Kir channel function among SeSAME syndrome mutations.

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    ABSTRACT: The inwardly rectifying potassium (Kir) channel subunit Kir4.1 is specifically expressed in brain astrocytes and Kir4.1-containing channels (Kir4.1 channels) mediate astroglial spatial potassium (K +) buffering. Recent advances in Kir4.1 research revealed that Kir4.1 channels can serve as a novel therapeutic target for epilepsy. Specifically, reduced expression or dysfunction of Kir4.1 channels seems to be involved in generation of generalized tonic-clonic seizures (GTCS) in animal models of epilepsy and patients with temporal lobe epilepsy. In addition, recent clinical studies showed that loss-of-function mutations of human gene (KCNJ10) encoding Kir4.1 elicit " EAST " or " SeSAME " syndrome which manifests as GTCS and ataxia. Although the precise mechanisms remain to be clarified, it is suggested that dysfunction of Kir4.1 channels disrupts spatial K + buffering by astrocytes, elevates extracellular levels of K + and/or glutamate and causes abnormal excitation of neurons in the limbic regions and neocortex. All these findings suggest that agents that activate or up-regulateastroglialKir4.1 channels would be effective for epilepsy. In addition, docking simulation analysis usingtheKir4.1 homology model provide simportant information for designing new Kir4.1 ligands. Discovery of suchagents that activate or up-regulate Kir4.1 channels would be a novel approach for the treatment of epilepsy.
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    ABSTRACT: .Background: The inwardly rectifying potassium channel subunit Kir4.1 is specifically expressed in astrocytes, which mediates spatial K+ buffering and is implicated in the pathogenesis of convulsive epileptic disorders (i.e. generalized tonic-clonic (GTC) and temporal lobe seizures). Objectives: This study aimed to explore the pathophysiological role of Kir4.1 channels in modulating absence seizure incidence, using a spontaneously epileptic animal model. Materials and Methods: Groggy rats, a rat model of human absence seizures, and Slc:Wistar (control) rats, were used in this study. Cortical and hippocampal EEG were recorded to confirm the seizure incidence in Groggy rats. The expression levels of Kir subunits (i.e. Kir4.1, Kir5.1 and Kir2.1) in ten brain regions were analyzed by Western blotting. Results: Groggy rats showed a high incidence (ca. 350 seconds total duration/15 minutes observation period) of absence-like seizures, which were characterized by a sudden immobile posture and synchronously-associated spike and wave discharges. However, Western blot analysis revealed that Kir4.1 expression in Groggy rats was not significantly different from that of control rats in any of the brain regions examined (e.g. cerebral cortex, striatum, hippocampus, diencephalon, midbrain, pons/medulla oblongata and cerebellum). In addition, expressional levels of Kir5.1 and Kir2.1, which are also expressed in astrocytes, were unaltered in Groggy rats. Conclusions: The present results suggest that unlike GTC and temporal lobe seizures, pathophysiological alterations (e.g. dysfunction and/or expressional changes) of Kir4.1 are not linked to non-convulsive absence seizures.
    01/2014; 2(1):e18651. DOI:10.5812/archneurosci.1865

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