Kv1.2 Channels at the Interface of Redox and Electrical Excitability

Abstract

Kv1.2 is a prominent neuronal potassium channel subtype linked to severe epilepsies and movement disorders. We have demonstrated that neuronal and heterologously-expressed Kv1.2 channels exhibit use-dependent activation, a behavior characterized by progressive potentiation of channel activity during trains of repetitive stimuli. Use-dependent activation arises from a gating mode shift from a ‘reluctant’ slowly-activating mode to a ‘willing’ rapidly-activating mode with hyperpolarized voltage-dependence of activation. Moreover, Kv1.2 subunits recruit this use-dependent phenotype to heteromeric channel complexes. In this study, we demonstrate that use-dependent activation of Kv1.2 channel complexes is strongly regulated by a variety of exogenous and physiological redox species. Under ambient redox conditions, Kv1.2 channels exhibit marked cell-to-cell variability of use-dependent activation. However, exposure to mild reducing conditions normalizes this response, such that a pronounced use-dependent phenotype is consistently observed, together with a dramatic depolarizing shift of voltage-dependent activation with a V1/2 of 51+/- 6 mV. Mutagenesis of candidate cysteine residues in Kv1.2 did not affect redox sensitivity, therefore we hypothesize a role for an extrinsic redox-sensitive interacting partner. Using a variety of redox buffers, we demonstrate that use-dependent activation is steeply regulated by redox potentials between −50 and −100 mV, within the typical extracellular range. Furthermore, effects of membrane-impermeable reducing agents demonstrate that use-dependent activation is regulated by the extracellular redox state. Taken together, these findings suggest that Kv1.2 is a unique transducer of the extracellular environment, and may translate altered extracellular redox conditions to changes in cellular electrical function.