Deletion Of The Amino-Terminus Uncovers An Inactivated State In Eag1 Channels

Ether-a-go-go (Eag) family channels are voltage-gated K+ channels that are important in cardiac and neural function and have a well-documented role in disease. One of eight members of the mammalian Eag family, EAG1 channels expression is confined to the central nervous system of the healthy adult. EAG1 channels are also expressed in cancer cells and are implicated in tumor progression and regulation of the cell cycle. Most members of the Eag channel family exhibit voltage-dependent inactivation, yet wild-type EAG1 channels exhibit only voltage-gated activation and deactivation, with no apparent inactivation. Here we report that deletion of the entire intracellular amino-terminal domain uncovers an inactivated channel gating state at depolarizing potentials. We characterized this inactivated state in excised patches from Xenopus oocytes expressing mutant EAG1 channels, and recorded their currents in the inside-out configuration of the patch clamp technique. Similar to wild-type channels, EAG1 with a deleted amino-terminus begins to activate around −80 mV, however, these channels also inactivate at potentials higher than −40 mV. The rate of inactivation becomes faster with increasingly depolarizing potentials. Additionally, the kinetics of the EAG1 channels with a deleted amino-terminus are quite slow. Other members of the Eag family of channels exhibit C-type inactivation, which results from collapse of the selectivity filter. To determine whether the inactivation found in this EAG1 mutant was also C-type, we mutated a pore-lining residue known to alter C-type inactivation in both Shaker and hERG1 channels. As a second approach, we asked whether triethylammonium applied to the external surface of the channel altered the rate of inactivation. Results from both experiments are inconsistent with C-type inactivation. Instead, we hypothesize that inactivation in the EAG1 channel lacking their amino-terminus is simply a reclosure of the activation gate.