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

Abstract

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.

• Authors: Ruth Rea, Alexander Spauschus, Louise H Eunson, Michael G Hanna, Dimitri M Kullmann
• Journal: The Journal of physiology (J Physiol) Vol. 538 Issue Pt 1 Pg. 5-23 (Jan 01 2002) ISSN: 0022-3751 [Print] England
• PMID: 11773313 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• KCNA1 protein, human
• Kv1.2 Potassium Channel
• Potassium Channel Blockers
• Potassium Channels
• Potassium Channels, Voltage-Gated
• Kv1.1 Potassium Channel
• Tetraethylammonium

Topics

• Animals
• Electrophysiology
• Female
• Fluorescence
• Humans
• Kinetics
• Kv1.1 Potassium Channel
• Kv1.2 Potassium Channel
• Models, Biological
• Mutation (physiology)
• Oocytes
• Patch-Clamp Techniques
• Potassium Channel Blockers (pharmacology)
• Potassium Channels (drug effects, genetics, physiology)
• Potassium Channels, Voltage-Gated
• Protein Processing, Post-Translational
• Reference Values
• Tetraethylammonium (pharmacology)
• Xenopus laevis