Kv3.1/Kv3.2 channel positive modulators enable faster activating kinetics and increase firing frequency in fast-spiking GABAergic interneurons. (15th May 2017) - Boddum, Kim
Abstract: Due to their fast kinetic properties, Kv 3.1 voltage gated potassium channels are important in setting and controlling firing frequency in neurons and pivotal in generating high frequency firing of interneurons. Pharmacological activation of Kv 3.1 channels may possess therapeutic potential for treatment of epilepsy, hearing disorders, schizophrenia and cognitive impairments. Here we thoroughly investigate the selectivity and positive modulation of the two small molecules, EX15 and RE01, on Kv 3 channels. Selectivity studies, conducted in Xenopus laevis oocytes confirmed a positive modulatory effect of the two compounds on Kv 3.1 and to a minor extent on Kv 3.2 channels. RE01 had no effect on the Kv 3.3 and Kv 3.4 channels, whereas EX15 had an inhibitory impact on the Kv 3.4 mediated current. Voltage-clamp experiments in monoclonal hKv 3.1b/HEK293 cells (34 °C) revealed that the two compounds indeed induced larger currents and faster activation kinetics. They also decrease the speed of deactivation and shifted the voltage dependence of activation, to a more negative activation threshold. Application of action potential clamping and repetitive stimulation protocols of hKv 3.1b expressing HEK293 cells revealed that EX15 and RE01 significantly increased peak amplitude, half width and decay time of Kv 3.1 mediated currents, even during high-frequency action potential clamping (250 Hz). In rat hippocampal slices, EX15 and RE01 increased neuronal excitability in fast-spiking interneurons in dentate gyrus. Action potential frequency was prominently increased at minor depolarizing steps, whereas more marginal effects of EX15 and RE01 were observed after stronger depolarizations. In conclusion, our results suggest that EX15 and RE01 positive modulation of Kv 3.1 and Kv 3.2 currents facilitate increased firing frequency in fast-spiking GABAergic interneurons. Highlights: We show a selective profile of the positive modulators, EX15 and RE01, among the Kv 3 channel subtypes. EX15 and RE01 increased Kv 3.1/Kv 3.2 channel currents, activation kinetics and shifted the voltage dependence of activation. Positive modulation of Kv 3.1/Kv 3.2 channels can increase the intrinsic firing frequency of fast-spiking interneurons.