Alexander Spauschus | PubMed Health

PubMed2006

Potassium channel dysfunction and depolarized resting membrane potential in a cell model of SCA3.

Spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant inherited neurodegenerative disease caused by the expansion of a polyglutamine repeat within the disease protein, ataxin-3. There is growing evidence that neuronal electrophysiological properties are altered in a variety of polyglutamine diseases such as Huntington's disease and SCA1 and that these alterations may contribute to disturbances of neuronal function prior to neurodegeneration. To elucidate possible electrophysiological changes in SCA3, we generated a stable PC12 cell model with inducible expression of normal and mutant human full-length ataxin-3 and analyzed the electrophysiological properties after induction of the recombinant ataxin-3 expression. Neuronally differentiated PC12 cells expressing the expanded form of ataxin-3 showed significantly decreased viabilities and developed ultrastructural changes resembling human SCA3. Prior to neuronal cell death, we found a significant reduction of the resting membrane potential and a hyperpolarizing shift of the activation curve of the delayed rectifier potassium current. These findings indicate that electrophysiological properties are altered in mutant ataxin-3 expressing neuronal cells and may contribute to neuronal dysfunction in SCA3.

Analysis of Variance↗

PubMed2002

Variable K(+) channel subunit dysfunction in inherited mutations of KCNA1.

Mutations of KCNA1, which codes for the K(+) channel subunit hKv1.1, are associated with the human autosomal dominant disease episodic ataxia type 1 (EA1). Five recently described mutations are associated with a broad range of phenotypes: neuromyotonia alone or with seizures, EA1 with seizures, or very drug-resistant EA1. Here we investigated the consequences of each mutation for channel assembly, trafficking, gating and permeation. We related data obtained from co-expression of mutant and wild-type hKv1.1 to the results of expressing mutant-wild-type fusion proteins, and combined electrophysiological recordings in Xenopus oocytes with a pharmacological discrimination of the contribution of mutant and wild-type subunits to channels expressed at the membrane. We also applied confocal laser scanning microscopy to measure the level of expression of either wild-type or mutant subunits tagged with green fluorescent protein (GFP). R417stop truncates most of the C-terminus and is associated with severe drug-resistant EA1. Electrophysiological and pharmacological measurements indicated that the mutation impairs both tetramerisation of R417stop with wild-type subunits, and membrane targeting of heterotetramers. This conclusion was supported by confocal laser scanning imaging of enhanced GFP (EGFP)-tagged hKv1.1 subunits. Co-expression of R417stop with wild-type hKv1.2 subunits yielded similar results to co-expression with wild-type hKv1.1. Mutations associated with typical EA1 (V404I) or with neuromyotonia alone (P244H) significantly affected neither tetramerisation nor trafficking, and only altered channel kinetics. Two other mutations associated with a severe phenotype (T226R, A242P) yielded an intermediate result. The phenotypic variability of KCNA1 mutations is reflected in a wide range of disorders of channel assembly, trafficking and kinetics.

Animals↗