Effect of tyrphostin AG879 on K_v4.2 and K_v4.3 potassium channels

Background and Purpose A-type potassium channels (I_A) are important proteins for modulating neuronal membrane excitability. The expression and activity of K_v4.2 channels are critical for neurological functions and pharmacological inhibitors of K_v4.2 channels may have therapeutic potential for Fragile X syndrome. While screening various compounds, we identified tyrphostin AG879, a tyrosine kinase inhibitor, as a K_v4.2 inhibitor from. In the present study we characterized the effect of AG879 on cloned K_v4.2/K_v channel-interacting protein 2 (KChIP2) channels. Experimental Approach To screen the library of pharmacologically active compounds, the thallium flux assay was performed on HEK-293 cells transiently-transfected with K_v4.2 cDNA using the Maxcyte transfection system. The effects of AG879 were further examined on CHO-K1 cells expressing K_v4.2/KChIP2 channels using a whole-cell patch-clamp technique. Key Results Tyrphostin AG879 selectively and dose-dependently inhibited K_v4.2 and K_v4.3 channels. In K_v4.2/KChIP2 channels, AG879 induced prominent acceleration of the inactivation rate, use-dependent block and slowed the recovery from inactivation. AG879 induced a hyperpolarizing shift in the voltage-dependence of the steady-state inactivation of K_v4.2 channels without apparent effect on the V_1/2 of the voltage-dependent activation. The blocking effect of AG879 was enhanced as channel inactivation increased. Furthermore, AG879 significantly inhibited the A-type potassium currents in the cultured hippocampus neurons. Conclusion and Implications AG879 was identified as a selective and potent inhibitor the K_v4.2 channel. AG879 inhibited K_v4.2 channels by preferentially interacting with the open state and further accelerating their inactivation.