title: Mesoridazine: an open-channel blocker of human ether-a-go-go-related gene K+ channel.
abstract: Mesoridazine, a phenothiazine antipsychotic agent, prolongs the QT interval of the cardiac electrocardiogram and is associated with Torsade de pointes-type arrhythmias. In this study, we examined the effects of mesoridazine on human ether-a-go-go-related gene (HERG) K+ currents. HERG channels were stably expressed in human embryonic kidney 293 cells and studied using standard whole-cell patch-clamp technique (37 degrees C). Mesoridazine blocked HERG currents in a concentration-dependent manner (IC50 550 nM at 0 mV); block increased significantly over the voltage range where HERG activates and saturated at voltages eliciting maximal HERG channel activation. Tonic block of HERG current by mesoridazine (1.8 microM) was minimal (< 2-4%). The rate of the onset of HERG channel block was rapid and dose dependent (tau = 54 +/- 7 ms at 0 mV and 1.8 microM mesoridazine), but not significantly affected by test potentials ranging from -30 to +30 mV. The V1/2 for steady-state activation was shifted from -31.2 +/- 1.0 to -39.2 +/- 0.5 mV (P < 0.01). The apparent rate of HERG channel deactivation was significantly reduced (fast tau = 153 +/- 8 vs. 102 +/- 6 ms at -50 mV, P < 0.01; slow tau = 1113 +/- 63 vs. 508 +/- 27 ms, P < 0.01). The inactivation kinetics and voltage dependence of steady-state inactivation of the HERG channel were not significantly altered by mesoridazine. These findings demonstrate that mesoridazine is a potent and rapid open-channel blocker of HERG channels. This block would explain the QT prolongation seen clinically at therapeutic concentrations (0.3-3.6 microM).
authors.affiliation: Department of Integrative Pharmacology, Abbott Laboratories, Abbott Park, IL 60064, USA. zhi.su@abbott.com
authors.forename: Zhi
authors.initials: Z
authors.lastname: Su
authors.forename: Ruth
authors.initials: R
authors.lastname: Martin
authors.forename: Bryan F
authors.initials: BF
authors.lastname: Cox
authors.forename: Gary
authors.initials: G
authors.lastname: Gintant
mesh_terms: D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D004553:Electric Conductivity; D022062:Electrophysiologic Techniques, Cardiac; D051638:Ether-A-Go-Go Potassium Channels; D006801:Humans; D007700:Kinetics; D008653:Mesoridazine / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D013997:Time Factors
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D008653:Mesoridazine; D011188:Potassium