Slo2/KNaChannels inDrosophilaProtect against Spontaneous and Induced Seizure-like Behavior Associated with an Increased Persistent Na+Current

Na+sensitivity is a unique feature of Na+-activated K+(KNa) channels, making them naturally suited to counter a sudden influx in Na+ions. As such, it has long been suggested that KNachannels may serve a protective function against excessive excitation associated with neuronal injury and disease. This hypothesis, however, has remained largely untested. Here, we examine KNachannels encoded by theDrosophila Slo2(dSlo2) gene in males and females. We show that dSlo2/KNachannels are selectively expressed in cholinergic neurons in the adult brain, as well as in glutamatergic motor neurons, where dampening excitation may function to inhibit global hyperactivity and seizure-like behavior. Indeed, we show that effects of feedingDrosophilaa cholinergic agonist are exacerbated by the loss of dSlo2/KNachannels. Similar to mammalian Slo2/KNachannels, we show that dSlo2/KNachannels encode a TTX-sensitive K+conductance, indicating that dSlo2/KNachannels can be activated by Na+carried by voltage-dependent Na+channels. We then tested the role of dSlo2/KNachannels in established genetic seizure models in which the voltage-dependent persistent Na+current (INap) is elevated. We show that the absence of dSlo2/KNachannels increased susceptibility to mechanically induced seizure-like behavior. Similar results were observed in WT flies treated with veratridine, an enhancer of INap. Finally, we show that loss of dSlo2/KNachannels in both genetic and pharmacologically primed seizure models resulted in the appearance of spontaneous seizures. Together, our results support a model in which dSlo2/KNachannels, activated by neuronal overexcitation, contribute to a protective threshold to suppress the induction of seizure-like activity.SIGNIFICANCE STATEMENTSlo2/KNachannels are unique in that they constitute a repolarizing K+pore that is activated by the depolarizing Na+ion, making them naturally suited to function as a protective “brake” against overexcitation and Na+overload. Here, we test this hypothesisin vivoby examining how a null mutation of theDrosophila Slo2(dSlo2)/KNagene affects seizure-like behavior in genetic and pharmacological models of epilepsy. We show that indeed the loss of dSlo2/KNachannels results in increased incidence and severity of induced seizure behavior, as well as the appearance of spontaneous seizure activity. Our results advance our understanding of neuronal excitability and protective mechanisms that preserve normal physiology and the suppression of seizure susceptibility.