Ca²⁺-permeable AMPA receptor-dependent silencing of neurons by KCa3.1 channels during epileptiform activity

Ca²⁺-activated KCa3.1 channels are known to contribute to slow afterhyperpolarization in pyramidal neurons of several brain areas, while Ca²⁺-permeable AMPA receptors (CP-AMPARs) may provide a subthreshold source of Ca²⁺ elevation in the cytoplasm. The functionality of these two types of channels has also been shown to be altered by epileptic disorders. However, the link between KCa3.1 channels and CP-AMPARs is poorly understood, and their potential interaction in epilepsy remains unclear. Here, we address this issue by overexpressing the KCNN4 gene, which encodes the KCa3.1 channel, using patch clamp, imaging, and channel blockers in an in vitro model of epilepsy in neuronal culture. We show that KCNN4 overexpression causes strong hyperpolarization and substantial silencing of neurons during epileptiform activity events, which also prevents KCNN4-positive neurons from firing action potentials (APs) during experimentally induced status epilepticus. Intracellular blocker application experiments showed that the amplitude of hyperpolarization was strongly dependent on CP-AMPARs, but not on NMDA receptors. Taken together, our data strongly suggest that subthreshold Ca²⁺ elevation produced by CP-AMPARs can trigger KCa3.1 channels to hyperpolarize neurons and protect them from seizures.