Histidine at position 462 determines the low quinine sensitivity of ether-à-go-go (Eag) channel superfamily member Kv 12.1.

BACKGROUND AND PURPOSE:The ether-à-go-go (Eag) Kv superfamily comprises closely-related Kv 10, Kv 11 and Kv 12 subunits. Kv 11.1 (termed hERG in humans) gained much attention, as these channels are highly susceptible to drug-induced inhibition constituting a frequent cause of acquired LQT syndrome and sudden death in humans. The exclusive drug sensitivity of Kv 11.1 can be explained by central drug binding pockets that are absent in most other channels. Currently, it is unknown whether Kv 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 Kv 12.1 channels to quinine, a substituted quinoline that blocks Kv 10.1 and Kv 11.1 at low micromolar concentrations. KEY RESULTS:Quinine inhibited Kv 12.1, but their affinity was 10-fold lower than for Kv 11.1. Contrary to Kv 11.1, quinine inhibited Kv 12.1 in a largely voltage-independent manner and induced channel opening at more depolarized potentials. Low sensitivity of Kv 12.1 and the characteristics of quinine-dependent inhibition were determined by histidine 462, as site-directed mutagenesis of this residue into the homologous tyrosine of Kv 11.1 conferred Kv 11.1-like quinine block to Kv 12.1(H462Y). Molecular modelling demonstrated that the low affinity of Kv 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 Kv 12.1(H462Y) and Kv 11.1 channels. CONCLUSION AND IMPLICATIONS:Our results showed that the quinoline binding "motif" is not conserved within the Eag superfamily, although the overall architecture of these channels apparently is similar. Our study highlights functional and pharmacological diversity in this group of evolutionary-conserved channels.