title: The membrane permeable calcium chelator BAPTA-AM directly blocks human ether a-go-go-related gene potassium channels stably expressed in HEK 293 cells.
abstract: BAPTA-AM is a well-known membrane permeable Ca(2+) chelator. The present study found that BAPTA-AM rapidly and reversibly suppressed human ether a-go-go-related gene (hERG or Kv11.1) K(+) current, human Kv1.3 and human Kv1.5 channel currents stably expressed in HEK 293 cells, and the effects were not related to Ca(2+) chelation. The externally applied BAPTA-AM inhibited hERG channels in a concentration-dependent manner (IC(50): 1.3 microM). Blockade of hERG channels was dependent on channel opening, and tonic block was minimal. Steady-state activation V(0.5) of hERG channels was negatively shifted by 8.5 mV (from -3.7+/-2.8 of control to -12.2+/-3.1 mV, P<0.01), while inactivation V(0.5) was negatively shifted by 6.1 mV (from -37.9+/-2.0 mV of control to -44.0+/-1.6 mV, P<0.05) with application of 3 microM BAPTA-AM. The S6 mutant Y652A and the pore helix mutant S631A significantly attenuated blockade by BAPTA-AM at 10 microM causing profound blockade of wild-type hERG channels. In addition, BAPTA-AM inhibited hKv1.3 and hKv1.5 channels in a concentration-dependent manner (IC(50): 1.45 and 1.23 microM, respectively), and the blockade of these two types of channels was also dependent on channel opening. Moreover, EGTA-AM was found to be an open channel blocker of hERG, hKv1.3, hKv1.5 channels, though its efficacy is weaker than that of BAPTA-AM. These results indicate that the membrane permeable Ca(2+) chelator BAPTA-AM (also EGTA-AM) exerts an open channel blocking effect on hERG, hKv1.3 and hKv1.5 channels.
authors.affiliation: Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Tang
authors.forename: Man-Wen
authors.initials: MW
authors.lastname: Jin
authors.forename: Ji-Zhou
authors.initials: JZ
authors.lastname: Xiang
authors.forename: Min-Qing
authors.initials: MQ
authors.lastname: Dong
authors.forename: Hai-Ying
authors.initials: HY
authors.lastname: Sun
authors.forename: Chu-Pak
authors.initials: CP
authors.lastname: Lau
authors.forename: Gui-Rong
authors.initials: GR
authors.lastname: Li
mesh_terms: D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000502:physiology*; D006801:Humans; D051664:Kv1.3 Potassium Channel / Q000235:genetics / Q000502:physiology; D051666:Kv1.5 Potassium Channel / Q000235:genetics / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D016297:Mutagenesis, Site-Directed; D018272:Porins / Q000235:genetics / Q000502:physiology; D014162:Transfection