Novel mechanism of EAG channel inhibition by imipramine.

Abstract

Ether-a-go-go (EAG) potassium channels regulate neuronal excitability and tumorigenesis. Upregulation of EAG channel activity is associated with severe neurological abnormalities and cancer. Therefore, studies of molecular mechanisms of EAG current inhibition have therapeutic importance. It has been reported that imipramine inhibits EAG channels by binding intracellularly inside the open pore of the channel (García-Ferreiro, et al., 2004, JGP). Recently we have shown that a tricyclic drug chlorpromazine inhibits EAG channels by binding to their intracellular N-terminal Per-Arnt-Sim (PAS) domain. Since both imipramine and chlorpromazine share high structural similarity and both belong to the tricyclic compound family, we tested if imipramine can also inhibit EAG channels via binding to the PAS domain. Our surface plasmon resonance based experiments showed that imipramine binds to the isolated PAS domain of EAG channels in a concentration-dependent manner. As reported before, we also observed imipramine concentration-dependent inhibition of currents from EAG channels recorded using two-electrode voltage-clamp technique. Importantly, the inhibition was substantially decreased for the mutant channels lacking the N-terminal PAS domain. These results indicate that, in addition to the open-pore inhibition mechanism, imipramine inhibits EAG channels via binding to the intracellular PAS domain. Our results suggest that the tricyclic compounds share a common mechanism of EAG channel inhibition via the intracellular PAS domains.