Effects of MiRP1 and DPP6 beta-subunits on the blockade induced by flecainide of Kv4.3/KChIP2 channels.
OBJECTIVE
The human cardiac transient outward potassium current (Ito) is believed to be composed of the pore-forming Kv4.3 alpha-subunit, coassembled with modulatory beta-subunits as KChIP2, MiRP1 and DPP6 proteins. beta-Subunits can alter the pharmacological response of Ito; therefore, we analysed the effects of flecainide on Kv4.3/KChIP2 channels coassembled with MiRP1 and/or DPP6 beta-subunits.


METHODS
Currents were recorded in Chinese hamster ovary cells stably expressing K(V)4.3/KChIP2 channels, and transiently transfected with either MiRP1, DPP6 or both, using the whole-cell patch-clamp technique.


RESULTS
In control conditions, Kv4.3/KChIP2/MiRP1 channels exhibited the slowest activation and inactivation kinetics and showed an 'overshoot' in the time course of recovery from inactivation. The midpoint values (Vh) of the activation and inactivation curves for Kv4.3/KChIP2/DPP6 and Kv4.3/KChIP2/MiRP1/DPP6 channels were approximately 10 mV more negative than Vh values for Kv4.3/KChIP2 and Kv4.3/KChIP2/MiRP1 channels. Flecainide (0.1-100 microM) produced a similar concentration-dependent blockade of total integrated current flow (IC50 approximately 10 microM) in all the channel complexes. However, the IC50 values for peak current amplitude and inactivated channel block were significantly different. Flecainide shifted the Vh values of both the activation and inactivation curves to more negative potentials and apparently accelerated inactivation kinetics in all channels. Moreover, flecainide slowed recovery from inactivation in all the channel complexes and suppressed the 'overshoot' in Kv4.3/KChIP2/MiRP1 channels.


CONCLUSIONS
Flecainide directly binds to the Kv4.3 alpha-subunit when the channels are in the open and inactivated state and the presence of the beta-subunits modulates the blockade by altering the gating function.
Radicke
S
S
Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain.
Vaquero
M
M
Caballero
R
R
Gómez
R
R
Núñez
L
L
Tamargo
J
J
Ravens
U
U
Wettwer
E
E
Delpón
E
E
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage / Q000494:pharmacology*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D004305:Dose-Response Relationship, Drug; D005260:Female; D005424:Flecainide / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D020128:Inhibitory Concentration 50; D051605:Kv Channel-Interacting Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010447:Peptide Hydrolases / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D021122:Protein Subunits; D051672:Shal Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D014162:Transfection
D000889:Anti-Arrhythmia Agents; C489619:KCNE2 protein, human; C496752:KCNIP2 protein, human; D051605:Kv Channel-Interacting Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; D051672:Shal Potassium Channels; C503535:DPP6 protein, human; D010447:Peptide Hydrolases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D005424:Flecainide