Dofetilide block involves interactions with open and inactivated states of HERG channels

Rapidly activating delayed rectifier current (IKr) is the key target of class III antiarrhythmic drugs including dofetilide. Due to its complex gating properties, the precise channel state or states that interact with these agents remain poorly defined. We have undertaken a careful analysis of the state dependence of HERG channel block by dofetilide in Xenopus oocytes and Chinese Hamster Ovary (CHO) cells by devising a protocol in which brief sampling pulses were superimposed over a wide range of test potentials. The rate of block onset, maximal steady-state block and IC50 were similar for all test potentials over the activation range, demonstrating that the drug probably interacts with open and/or inactivated but not resting HERG channels with high affinity. Reducing the fraction of inactivated channels at 0 mV by augmenting the external potassium concentration did not alter the sensitivity to dofetilide. In contrast, the S631A and S620T HERG mutations both eliminated inward rectification and reduced dofetilide affinity by ≅10- and ≅100-fold respectively. We have also found a novel ultra-slow activation process which occurs in wild type HERG channels at threshold potentials. Overall, our data imply that dofetilide block occurs equally at all voltages positive to the activation threshold, and that the drug interacts with HERG channels in both the open and inactivated states.

[1]  M. Sanguinetti,et al.  Spectrum of HERG K+-channel dysfunction in an inherited cardiac arrhythmia. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[2]  A. Brown,et al.  Pathways of HERG inactivation. , 1999, American journal of physiology. Heart and circulatory physiology.

[3]  G. Robertson,et al.  HERG, a human inward rectifier in the voltage-gated potassium channel family. , 1995, Science.

[4]  E. Carmeliet.  Voltage- and time-dependent block of the delayed K+ current in cardiac myocytes by dofetilide. , 1992, The Journal of pharmacology and experimental therapeutics.

[5]  A. Brown,et al.  Molecular physiology and pharmacology of HERG. Single-channel currents and block by dofetilide. , 1996, Circulation.

[6]  D. Roden,et al.  Extracellular potassium modulation of drug block of IKr. Implications for torsade de pointes and reverse use-dependence. , 1996, Circulation.

[7]  Qiuming Gong,et al.  Blockage of the HERG human cardiac K+ channel by the gastrointestinal prokinetic agent cisapride. , 1997, American journal of physiology. Heart and circulatory physiology.

[8]  G M Briggs,et al.  Identification of a specific radioligand for the cardiac rapidly activating delayed rectifier K+ channel. , 1993, Circulation research.

[9]  M. Sanguinetti,et al.  Two components of cardiac delayed rectifier K+ current. Differential sensitivity to block by class III antiarrhythmic agents , 1990, The Journal of general physiology.

[10]  A. Brown,et al.  A mechanism for the proarrhythmic effects of cisapride (Propulsid): high affinity blockade of the human cardiac potassium channel HERG , 1997, FEBS letters.

[11]  A. Brown,et al.  HERG, a primary human ventricular target of the nonsedating antihistamine terfenadine. , 1996, Circulation.

[12]  John S. Mitcheson,et al.  Trapping of a Methanesulfonanilide by Closure of the Herg Potassium Channel Activation Gate , 2000, The Journal of general physiology.

[13]  E. Green,et al.  A molecular basis for cardiac arrhythmia: HERG mutations cause long QT syndrome , 1995, Cell.

[14]  H. Duff,et al.  [3H]dofetilide binding: biological models that manifest solely the high or the low affinity binding site. , 1996, Journal of molecular and cellular cardiology.

[15]  A. Brown,et al.  Molecular determinants of dofetilide block of HERG K+ channels. , 1998, Circulation research.

[16]  Jun Chen,et al.  A structural basis for drug-induced long QT syndrome. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[17]  M. Sanguinetti,et al.  Rate-dependent prolongation of cardiac action potentials by a methanesulfonanilide class III antiarrhythmic agent. Specific block of rapidly activating delayed rectifier K+ current by dofetilide. , 1993, Circulation research.

[18]  G. Robertson,et al.  Transfer of rapid inactivation and sensitivity to the class III antiarrhythmic drug E‐4031 from HERG to M‐eag channels , 1998, The Journal of physiology.

[19]  M. Sanguinetti,et al.  A mutation in the pore region of HERG K+ channels expressed in Xenopus oocytes reduces rectification by shifting the voltage dependence of inactivation , 1998, The Journal of physiology.

[20]  K. Koh,et al.  Torsade de pointes induced by terfenadine in a patient with long QT syndrome. , 1994, Journal of electrocardiology.

[21]  M. E. O'leary.  Inhibition of human ether-a-go-go potassium channels by cocaine. , 2001, Molecular pharmacology.

[22]  J. Balser,et al.  Probing the Interaction Between Inactivation Gating and d-Sotalol Block of HERG , 2000, Circulation research.

[23]  S. Heinemann,et al.  Molecular determinants for activation and inactivation of HERG, a human inward rectifier potassium channel. , 1996, The Journal of physiology.

[24]  M. Sanguinetti,et al.  A mechanistic link between an inherited and an acquird cardiac arrthytmia: HERG encodes the IKr potassium channel , 1995, Cell.

[25]  D M Roden,et al.  Ibutilide, a methanesulfonanilide antiarrhythmic, is a potent blocker of the rapidly activating delayed rectifier K+ current (IKr) in AT-1 cells. Concentration-, time-, voltage-, and use-dependent effects. , 1995, Circulation.

[26]  H. Duff,et al.  Molecular determinant of high-affinity dofetilide binding to HERG1 expressed in Xenopus oocytes: involvement of S6 sites. , 2000, Molecular pharmacology.

[27]  D. Snyders,et al.  High affinity open channel block by dofetilide of HERG expressed in a human cell line. , 1996, Molecular pharmacology.

[28]  H. Strauss,et al.  Modulation of HERG affinity for E‐4031 by [K+]o and C‐type inactivation , 1997, FEBS letters.

[29]  Gary Yellen,et al.  The inward rectification mechanism of the HERG cardiac potassium channel , 1996, Nature.

[30]  M. Sanguinetti,et al.  Class III antiarrhythmic drugs block HERG, a human cardiac delayed rectifier K+ channel. Open-channel block by methanesulfonanilides. , 1996, Circulation research.

[31]  H. Strauss,et al.  Time, voltage and ionic concentration dependence of rectification of h‐erg expressed in Xenopus oocytes , 1996, FEBS letters.