Calcium-Activated Potassium Channel K_Ca3.1 Shape Epileptiform Discharges in the Rodent Entorhinal Cortex

The mechanisms underlying the generation and termination of epileptic discharges remain incompletely understood. This study investigates the role of K_Ca3.1 (KCNN4) channels in modulating epileptiform activity in the deep layers of the entorhinal cortex using two in vitro models: short-lasting late recurrent discharges (LRDs) and prolonged tonic-clonic seizure-like events (SLEs). Whole-cell patch-clamp recordings in rodent brain slices revealed that blocking K_Ca3.1 channels with TRAM-34 increased neuronal excitability and firing frequency, enabling sustained firing at higher depolarizing currents. In the LRD model, TRAM-34 had no effect on the frequency or duration of spontaneously generated LRDs, likely due to the low intrinsic expression of K_Ca3.1 channels in the entorhinal cortex. However, NS-309, a positive modulator of K_Ca3.1 and SK channels, reduced LRD duration, while TRAM-34 prolonged LRDs induced by extracellular stimulation. In the SLE model, TRAM-34 increased SLE frequency and enhanced glutamatergic activity at SLE onset, indicating a more pronounced role of K_Ca3.1 channels during intense epileptiform activity. To address the function of K_Ca3.1 channels in glutamatergic neurons, we specifically overexpressed KCNN4 in these cells using a viral vector. Although overexpression did not abolish LRD generation, its duration and magnitude were significantly reduced, mirroring the effects of NS-309. These results demonstrate that the contribution of K_Ca3.1 channels to epileptiform activity depends on its temporal pattern, with minimal influence on short LRDs but greater effects on robust glutamatergic activity at SLE onset. Thus, K_Ca3.1 upregulation provides feedback mechanisms for the premature termination of epileptiform discharges, suggesting K_Ca3.1 channels as potential therapeutic targets.