l-364373 and Arrhythmias--Cardiac

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.

Topics: Amino Acid Substitution; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Benzodiazepines; Binding Sites; Humans; Ion Channel Gating; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Long QT Syndrome; Microinjections; Mutagenesis, Site-Directed; Mutation; Oocytes; Patch-Clamp Techniques; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Structure, Tertiary; Protein Subunits; Xenopus