Revealing a hidden conducting state by manipulating the intracellular domains in KV10.1 exposes the coupling between two gating mechanisms

The KCNH family of potassium channels serves relevant physiological functions in both excitable and non-excitable cells, reflected in the massive consequences of mutations or pharmacological manipulation of their function. This group of channels shares structural homology with other voltage-gated K+ channels. Still, the mechanisms of gating in this family show significant differences with respect to the canonical electromechanical coupling in these molecules. In particular, the large intracellular domains of KCNH channels play a crucial role in gating that is still only partly understood. Using KCNH1(KV10.1) as a model, we have characterized the behavior of a series of modified channels that the current models could not explain. With electrophysiological and biochemical methods combined with mathematical modeling, we show that the behavior of the mutants can be explained by the uncovering of an open state that is not detectable in the wild type, is accessed from deep closed states, and reflects an intermediate step along the chain of events leading to channel opening. This allowed us to study gating steps prior to opening, which, for example, explain the mechanism of gating inhibition by Ca2+-Calmodulin, and generate a gating model that describes the characteristic features of KCNH channels gating.