title: High affinity open channel block by dofetilide of HERG expressed in a human cell line.
abstract: In the long QT syndrome, excessive prolongation of the cardiac action potential leads to polymorphic ventricular tachycardia (torsades de pointes) and sudden death. Mutations in HERG have been identified as one of the causes of the chromosome 7-linked form of congenital long QT syndrome. The biophysical properties of currents recorded from HERG expressing Xenopus oocytes are similar to those of a cardiac K+ current, I(Kr), but the characteristic nanomolar methanesulfonanilide sensitivity has not been demonstrated. To determine the biophysical and pharmacological properties of HERG under experimental conditions similar to those used to study native cardiac currents, we examined currents expressed after expression of HERG in a human cell line, human embryonic kidney 293. Transfected cells display K+-selective outward currents that activated at membrane potentials positive to -50 mV with strongly voltage-dependent kinetics [time constant (tau) = 2 sec at -20 mV and 188 msec at +20 mV]. Marked inward rectification was observed for depolarizations positive to +0 mV, which was due to rapid channel inactivation (tau = 6 msec at +50 mV). The subsequent tail currents at -40 mV displayed an initial rising phase with tau = 10 msec, followed by a slow multiexponential decline. The EC50 for the methanesulfonanilide I(Kr) blocker dofetilide was 12 +/- 2 nM. Induction of block depended on depolarization beyond the threshold for channel opening. Time-dependent block developed slowly, with tau = 5.2 +/- 0.6 sec (300 nM) at +10 mV, and was delayed by stronger depolarizations. This pattern suggested that dofetilide preferentially blocks open (or activated) channels and that the fast inactivation may competitively slow the binding kinetics. The latter occurrence was further supported by a simplified mathematical model that addressed the impact on binding kinetics of fast inactivation. These results indicate that the HERG gene product encodes an alpha subunit that, when expressed in mammalian cells, displays both the major functional and pharmacological properties of native I(Kr). Dofetilide acts as a slow-onset/slow-offset open channel blocker of this current at nanomolar concentrations.
authors.affiliation: Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6602, USA. dirk.snyders@mcmail.vanderbilt.edu
authors.forename: D J
authors.initials: DJ
authors.lastname: Snyders
authors.forename: A
authors.initials: A
authors.lastname: Chaudhary
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D027682:Cation Transport Proteins; D002460:Cell Line; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics; D010627:Phenethylamines / Q000494:pharmacology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated; D013449:Sulfonamides / Q000494:pharmacology*; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014162:Transfection
chemical_list: D000889:Anti-Arrhythmia Agents; D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D010627:Phenethylamines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D013449:Sulfonamides; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; C063533:dofetilide