title: Altering extracellular potassium concentration does not modulate drug block of human ether-a-go-go-related gene (hERG) channels.
abstract: 1. Drug-induced block of the rapidly activating delayed rectifier K+ current (I(Kr)), encoded by human ether-a-go-go-related gene (hERG), has been linked to acquired long QT syndrome (aLQTS). Hypokalaemia is a recognized risk factor in aLQTS. To further understand why hypokalaemia is a risk factor in aLQTS, we examined the effect of [K+]o on drug block of the hERG potassium channel stably expressed in human embryonic kidney (HEK-293) cells using whole-cell voltage-clamp techniques. 2. The effects of selected [K+]o (1-20 mmol/L) on hERG block with four structurally diverse compounds (dofetilide, mesoridazine, quinidine and terfenadine) from different therapeutic classes were evaluated. Reducing [K+]o from 20 to 1 mmol/L had little effect on IC50 values for hERG current block for all four compounds. For example, evaluating quinidine in external potassium concentrations of 20, 10, 5 and 1 mmol/L resulted in IC50 values of 1.82 +/- 0.33, 2.04 +/- 0.28, 1.57 +/- 0.52 and 1.14 +/- 0.21 mmol/L, respectively. No statistically significant difference (P > 0.35, anova) was observed between drug block of hERG in different external potassium concentrations. These data are in contrast with previously reported results examining hERG channel modulation expressed in AT-1 cells under similar experimental conditions. 3. These results demonstrate that [K+]o does not directly modulate drug block of hERG channels expressed in an HEK-293 cell line. The enhanced risk of Torsades de Pointes associated with hypokalaemia in aLQTS may be due to reduction of other (non-hERG) potassium currents, further reducing the repolarization reserve, and not due to direct modulation of hERG block by [K+]o.
authors.affiliation: Department of Integrative Pharmacology, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois 60064-6119, USA. james.limberis@abbott.com
authors.forename: James T
authors.initials: JT
authors.lastname: Limberis
authors.forename: Zhi
authors.initials: Z
authors.lastname: Su
authors.forename: Bryan F
authors.initials: BF
authors.lastname: Cox
authors.forename: Gary A
authors.initials: GA
authors.lastname: Gintant
authors.forename: Ruth L
authors.initials: RL
authors.lastname: Martin
mesh_terms: D002460:Cell Line; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000187:drug effects*; D008653:Mesoridazine / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011802:Quinidine / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D016593:Terfenadine / Q000494:pharmacology
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D010627:Phenethylamines; D026902:Potassium Channel Blockers; D013449:Sulfonamides; D008653:Mesoridazine; D016593:Terfenadine; D011802:Quinidine; C063533:dofetilide; D011188:Potassium