Pharmacological activation of normal and arrhythmia-associated mutant KCNQ1 potassium channels.
KCNQ1 alpha-subunits coassemble with KCNE1 beta-subunits to form channels that conduct the slow delayed rectifier K+ current (IKs) important for repolarization of the cardiac action potential. Mutations in KCNQ1 reduce IKs and cause long-QT syndrome, a disorder of ventricular repolarization that predisposes affected individuals to arrhythmia and sudden death. Current therapy for long-QT syndrome is inadequate. R-L3 is a benzodiazepine that activates IKs and has the potential to provide gene-specific therapy. In the present study, we characterize the molecular determinants of R-L3 interaction with KCNQ1 channels, use computer modeling to propose a mechanism for drug-induced changes in channel gating, and determine its effect on several long-QT syndrome-associated mutant KCNQ1 channels heterologously expressed in Xenopus oocytes. Scanning mutagenesis combined with voltage-clamp analysis indicated that R-L3 interacts with specific residues located in the 5th and 6th transmembrane domains of KCNQ1 subunits. Most KCNQ1 mutant channels responded to R-L3 similarly to wild-type channels, but one mutant channel (G306R) was insensitive to R-L3 possibly because it disrupted a key component of the drug-binding site.
Seebohm
Guiscard
G
Department of Physiology and Eccles Program in Human Molecular Biology and Genetics, University of Utah, Salt Lake City, Utah 84112, USA.
Pusch
Michael
M
Chen
Jun
J
Sanguinetti
Michael C
MC
D019943:Amino Acid Substitution; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D001145:Arrhythmias, Cardiac / Q000235:genetics*; D001569:Benzodiazepines / Q000494:pharmacology; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D008133:Long QT Syndrome / Q000235:genetics; D008845:Microinjections; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D021122:Protein Subunits / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014981:Xenopus
D000889:Anti-Arrhythmia Agents; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; C113498:L 364373; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; D001569:Benzodiazepines