Effects of MiRP1 and DPP6 β-subunits on the blockade induced by flecainide of KV4.3/KChIP2 channels

Background and purpose: The human cardiac transient outward potassium current (I(to)) is believed to be composed of the pore-forming K(V)4.3 alpha-subunit, coassembled with modulatory beta-subunits as KChIP2, MiRP1 and DPP6 proteins. beta-Subunits can alter the pharmacological response of I(to); therefore, we analysed the effects of flecainide on K(V)4.3/KChIP2 channels coassembled with MiRP1 and/or DPP6 beta-subunits. Experimental approach: 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. Key results: In control conditions, K(V)4.3/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 (V(h)) of the activation and inactivation curves for K(V)4.3/KChIP2/DPP6 and K(V)4.3/KChIP2/MiRP1/DPP6 channels were approximate to 10mV more negative than V(h) values for K(V)4.3/KChIP2 and K(V)4.3/KChIP2/MiRP1 channels. Flecainide (0.1-100 mu M) produced a similar concentration-dependent blockade of total integrated current flow (IC(50) approximate to 10 mu M) in all the channel complexes. However, the IC(50) values for peak current amplitude and inactivated channel block were significantly different. Flecainide shifted the V(h) 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 K(V)4.3/KChIP2/MiRP1 channels. Conclusions and implications: 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.