A comparison of currents carried by HERG, with and without coexpression of MiRP1, and the native rapid delayed rectifier current. Is MiRP1 the missing link?

Although it has been suggested that coexpression of minK related peptide (MiRP1) is required for reconstitution of native rapid delayed‐rectifier current (IKr) by human ether‐a‐go‐go related gene (HERG), currents resulting from HERG (IHERG) and HERG plus MiRP1 expression have not been directly compared with native IKr. We compared the pharmacological and selected biophysical properties of IHERG with and without MiRP1 coexpression in Chinese hamster ovary (CHO) cells with those of guinea‐pig IKr under comparable conditions. Comparisons were also made with HERG expressed in Xenopus oocytes. MiRP1 coexpression significantly accelerated IHERG deactivation at potentials negative to the reversal potential, but did not affect more physiologically relevant deactivation of outward IHERG, which remained slower than that of IKr. MiRP1 shifted IHERG activation voltage dependence in the hyperpolarizing direction, whereas IKr activated at voltages more positive than IHERG. There were major discrepancies between the sensitivity to quinidine, E‐4031 and dofetilide of IHERG in Xenopus oocytes compared to IKr, which were not substantially affected by coexpression with MiRP1. On the other hand, the pharmacological sensitivity of IHERG in CHO cells was indistinguishable from that of IKr and was unaffected by MiRP1 coexpression. We conclude that the properties of IHERG in CHO cells are similar in many ways to those of native IKr under the same recording conditions, and that the discrepancies that remain are not reduced by coexpression with MiRP1. These results suggest that the physiological role of MiRP1 may not be to act as an essential consituent of the HERG channel complex carrying native IKr.

[1]  J. Nerbonne,et al.  Expression of Distinct ERG Proteins in Rat, Mouse, and Human Heart , 2000, The Journal of Biological Chemistry.

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

[3]  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.

[4]  H J Duff,et al.  Identification and characteristics of delayed rectifier K+ current in fetal mouse ventricular myocytes. , 1996, The American journal of physiology.

[5]  D A Terrar,et al.  Separation of the components of the delayed rectifier potassium current using selective blockers of IKr and IKs in guinea‐pig isolated ventricular myocytes , 1996, Experimental physiology.

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

[7]  J. Hancox,et al.  An investigation of the role played by the E-4031-sensitive (rapid delayed rectifier) potassium current in isolated rabbit atrioventricular nodal and ventricular myocytes , 1999, Pflügers Archiv.

[8]  E. Carmeliet.  Use-dependent block and use-dependent unblock of the delayed rectifier K+ current by almokalant in rabbit ventricular myocytes. , 1993, Circulation research.

[9]  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.

[10]  M. Lazdunski,et al.  KCNE2 confers background current characteristics to the cardiac KCNQ1 potassium channel , 2000, The EMBO journal.

[11]  M. Sanguinetti,et al.  Coassembly of K(V)LQT1 and minK (IsK) proteins to form cardiac I(Ks) potassium channel. , 1996, Nature.

[12]  D M Roden,et al.  Rapid inactivation determines the rectification and [K+]o dependence of the rapid component of the delayed rectifier K+ current in cardiac cells. , 1997, Circulation research.

[13]  N. Copeland,et al.  Two isoforms of the mouse ether-a-go-go-related gene coassemble to form channels with properties similar to the rapidly activating component of the cardiac delayed rectifier K+ current. , 1997, Circulation research.

[14]  Y Rudy,et al.  Two components of the delayed rectifier K+ current in ventricular myocytes of the guinea pig type. Theoretical formulation and their role in repolarization. , 1995, Circulation research.

[15]  L. Wang,et al.  Electrophysiological characterization of an alternatively processed ERG K+ channel in mouse and human hearts. , 1997, Circulation research.

[16]  M. Sanguinetti,et al.  Coassembly of KVLQT1 and minK (IsK) proteins to form cardiac IKS potassium channel , 1996, Nature.

[17]  M. Lazdunski,et al.  M‐type KCNQ2–KCNQ3 potassium channels are modulated by the KCNE2 subunit , 2000, FEBS letters.

[18]  S Nattel,et al.  Effects of the chromanol 293B, a selective blocker of the slow, component of the delayed rectifier K+ current, on repolarization in human and guinea pig ventricular myocytes. , 1998, Cardiovascular research.

[19]  J. R. Clay,et al.  A quantitative description of the E-4031-sensitive repolarization current in rabbit ventricular myocytes. , 1995, Biophysical journal.

[20]  R L Winslow,et al.  Molecular Interactions Between Two Long-QT Syndrome Gene Products, HERG and KCNE2, Rationalized by In Vitro and In Silico Analysis , 2001, Circulation research.

[21]  S. Nattel,et al.  Effects of the chromanol 293 B , a selective blocker of the slow , component of the delayed rectifier K q current , on repolarization in human and guinea pig ventricular myocytes , 1998 .

[22]  M. Keating,et al.  MiRP1 Forms IKr Potassium Channels with HERG and Is Associated with Cardiac Arrhythmia , 1999, Cell.

[23]  D M Roden,et al.  A common polymorphism associated with antibiotic-induced cardiac arrhythmia. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[24]  H. Strauss,et al.  Activation and inactivation kinetics of an E-4031-sensitive current from single ferret atrial myocytes. , 1996, Biophysical journal.

[25]  Jacques Barhanin,et al.  KvLQT1 and IsK (minK) proteins associate to form the IKS cardiac potassium current , 1996, Nature.

[26]  T. McDonald,et al.  Analysis of the Cyclic Nucleotide Binding Domain of the HERG Potassium Channel and Interactions with KCNE2* , 2001, The Journal of Biological Chemistry.

[27]  Stanley Nattel,et al.  Dofetilide block involves interactions with open and inactivated states of HERG channels , 2002, Pflügers Archiv - European Journal of Physiology.

[28]  Glenn I. Fishman,et al.  Cyclic AMP regulates the HERG K+ channel by dual pathways , 2000, Current Biology.

[29]  Gea-Ny Tseng,et al.  MinK-Related Peptide 1 Associates With Kv4.2 and Modulates Its Gating Function: Potential Role as &bgr; Subunit of Cardiac Transient Outward Channel? , 2001, Circulation research.