Unusual suspects underlying multimodal gating of Kv1.2 channels.

Abstract

Kv1.2 has been a widely used model for structural interpretations of voltage-dependent gating. Less appreciated is that Kv1.2 exhibits pronounced variability in its gating properties in different expression systems, and this is likely controlled by multiple regulatory pathways. We have undertaken a discovery-based approach using mass spectrometry and electrophysiological screening to identify proteins that influence the kinetics and voltage-dependence of Kv1.2 gating. Surprisingly, the Slc7a5 amino acid transporter exerts powerful effects on both Kv1.1 and Kv1.2 channels, including a prominent hyperpolarizing shift of voltage-dependent activation and accelerated inactivation. Although we do not yet understand the detailed structural basis of this modulation, we have identified mutations in the S1 segment of the Kv1.1 and Kv1.2 voltage sensors that abolish Slc7a5 sensitivity. Additionally, Slc7a5 modulation is antagonized by a second mechanism that underlies redox sensitivity specific to Kv1.2. In extracellular reducing conditions, Kv1.2 exhibits a large depolarizing shift of voltage-dependent activation, opposite to the effect of Slc7a5. The interaction of redox sensitivity with Slc7a5 modulation generates complex voltage-dependence of channel activity over an extraordinarily broad range of physiological voltages. These observations illustrate that Kv1.2 is prone to powerful modulation by unexpected protein partners.