Abstract
BACKGROUND AND PURPOSE: The ether-à-go-go (Eag) K(v) superfamily comprises closely related K(v) 10, K(v) 11, and K(v) 12 subunits. K(v) 11.1 (termed hERG in humans) gained much attention, as drug-induced inhibition of these channels is a frequent cause of sudden death in humans. The exclusive drug sensitivity of K(v) 11.1 can be explained by central drug-binding pockets that are absent in most other channels. Currently, it is unknown whether K(v) 12 channels are equipped with an analogous drug-binding pocket and whether drug-binding properties are conserved in all Eag superfamily members. EXPERIMENTAL APPROACH: We analysed sensitivity of recombinant K(v) 12.1 channels to quinine, a substituted quinoline that blocks K(v) 10.1 and K(v) 11.1 at low micromolar concentrations. KEY RESULTS: Quinine inhibited K(v) 12.1, but its affinity was 10-fold lower than for K(v) 11.1. Contrary to K(v) 11.1, quinine inhibited K(v) 12.1 in a largely voltage-independent manner and induced channel opening at more depolarised potentials. Low sensitivity of K(v) 12.1 and characteristics of quinine-dependent inhibition were determined by histidine 462, as site-directed mutagenesis of this residue into the homologous tyrosine of K(v) 11.1 conferred K(v) 11.1-like quinine block to K(v) 12.1(H462Y). Molecular modelling demonstrated that the low affinity of K(v) 12.1 was determined by only weak interactions of residues in the central cavity with quinine. In contrast, more favourable interactions can explain the higher quinine sensitivity of K(v) 12.1(H462Y) and K(v) 11.1 channels. CONCLUSIONS AND IMPLICATIONS: The quinoline-binding "motif" is not conserved within the Eag superfamily, although the overall architecture of these channels is apparently similar. Our findings highlight functional and pharmacological diversity in this group of evolutionary-conserved channels.