title: Trapping of a methanesulfonanilide by closure of the HERG potassium channel activation gate.
abstract: Deactivation of voltage-gated potassium (K(+)) channels can slow or prevent the recovery from block by charged organic compounds, a phenomenon attributed to trapping of the compound within the inner vestibule by closure of the activation gate. Unbinding and exit from the channel vestibule of a positively charged organic compound should be favored by membrane hyperpolarization if not impeded by the closed gate. MK-499, a methanesulfonanilide compound, is a potent blocker (IC(50) = 32 nM) of HERG K(+) channels. This bulky compound (7 x 20 A) is positively charged at physiological pH. Recovery from block of HERG channels by MK-499 and other methanesulfonanilides is extremely slow (Carmeliet 1992; Ficker et al. 1998), suggesting a trapping mechanism. We used a mutant HERG (D540K) channel expressed in Xenopus oocytes to test the trapping hypothesis. D540K HERG has the unusual property of opening in response to hyperpolarization, in addition to relatively normal gating and channel opening in response to depolarization (Sanguinetti and Xu 1999). The hyperpolarization-activated state of HERG was characterized by long bursts of single channel reopening. Channel reopening allowed recovery from block by 2 microM MK-499 to occur with time constants of 10.5 and 52.7 s at -160 mV. In contrast, wild-type HERG channels opened only briefly after membrane hyperpolarization, and thus did not permit recovery from block by MK-499. These findings provide direct evidence that the mechanism of slow recovery from HERG channel block by methanesulfonanilides is due to trapping of the compound in the inner vestibule by closure of the activation gate. The ability of HERG channels to trap MK-499, despite its large size, suggests that the vestibule of this channel is larger than the well studied Shaker K(+) channel.
authors.affiliation: Department of Medicine, Division of Cardiology, Eccles Institute of Human Genetics, University of Utah, Salt Lake City, Utah 84112, USA. john.mitcheson@hci.utah.edu
authors.forename: J S
authors.initials: JS
authors.lastname: Mitcheson
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.forename: M C
authors.initials: MC
authors.lastname: Sanguinetti
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D001578:Benzopyrans / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D027682:Cation Transport Proteins; D004305:Dose-Response Relationship, Drug; D051638:Ether-A-Go-Go Potassium Channels; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D020125:Mutation, Missense; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D014981:Xenopus
chemical_list: D000889:Anti-Arrhythmia Agents; D001578:Benzopyrans; D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; C092509:KCNH6 protein, human; D010880:Piperidines; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C087257:L 706000