Use-Dependent Activation of Kv1.2 Channel Complexes

Abstract

In excitable cells, ion channels are often challenged by rapid and repetitive stimuli. Ion channel responses to repetitive stimulation shape cellular behaviors by regulating the duration and termination of bursting action potentials. Therefore, we have investigated the regulation of voltage-gated potassium (Kv) channels under high frequency stimuli, with a particular focus on the canonical delayed rectifier Kv1.2. Previous reports have demonstrated a unique prepulse potentiation behavior that is observed in Kv1.2 channels expressed in mammalian cell lines. In this study, we demonstrate that this prepulse potentiation enables Kv1.2 channels to exhibit marked use-dependent activation, with trains of brief depolarizations causing dramatic increases in elicited current. This property arises from a stabilization of the channel open state in potentiated channels by ∼2.5 kcal/mol, reflecting a 28 ± 1 mV leftward shift in activation V1/2 after channel potentiation, and a marked acceleration of channel activation. Importantly, Kv subunits can assemble into heteromeric channels, generating diversity of function and sensitivity to signaling mechanisms. We demonstrate that although other Kv1 channel types are not prone to the use-dependent activation observed for Kv1.2, this property is conferred to other Kv1 subunits when they co-assemble with Kv1.2 in heteromeric channels. Our observations suggest a unique role for Kv1.2 subunits as potential suppressive components of heteromeric Kv1 channels, and describe a novel mechanism of channel regulation that will influence channel activity during bursts of cellular electrical activity. These findings illustrate that the functional output of heteromeric Kv channels integrates the biophysical properties and signaling sensitivities of their component subunits. We highlight the importance of expanding biophysical studies of Kv channels to better understand interactions between different subunit types in heteromeric complexes.