Due to their fast kinetic properties, K v 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 K v 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 K v 3 channels. Selectivity studies, conducted in Xenopus laevis oocytes confirmed a positive modulatory effect of the two compounds on K v 3.1 and to a minor extent on K v 3.2 channels. RE01 had no effect on the K v 3.3 and K v 3.4 channels, whereas EX15 had an inhibitory impact on the K v 3.4 mediated current.

Voltage-clamp experiments in monoclonal hK v 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 hK v 3.1b expressing HEK293 cells revealed that EX15 and RE01 significantly increased peak amplitude, half width and decay time of K v 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.