In vivo treatment with the casein kinase 2 inhibitor 4,5,6,7‐tetrabromotriazole augments the slow afterhyperpolarizing potential and prevents acute epileptiform activity

Abstract

SUMMARYObjective: The slow afterhyperpolarizing potential (sAHP) following prolonged depolarization is a major intrinsic mechanism of neuronal inhibition, by powerfully dampening excitability for up to 2 s. Therefore, an altered sAHP function might be vulnerable to hyperexcitable states such as epilepsy. Here, we have investigated the role of casein kinase 2 (CK2) on the sAHP in control and chronically epileptic tissue. Methods: Using the rat pilocarpine model of chronic temporal lobe epilepsy, we performed whole-cell patch-clamp recordings of acutely isolated CA1 pyramidal cells and field potential measurements on hippocampal slices. Results: Chronic oral administration of the CK2 inhibitor 4,5,6,7-tetrabromotriazole (TBB) for 4 days prior to brain dissection caused a significant increase of the sAHPmediating current in both control and epileptic tissues. In contrast, when TBB was acutely applied during the patch-clamp recording, the sAHP remained unaltered, indicating that chronic CK2 inhibition was required for sAHP augmentation. To test whether CK2 inhibition also has an anticonvulsive effect, we evoked recurrent epileptiform discharges (REDs) in hippocampal slice preparations by Mg 2+ removal. It is important to note that chronic oral TBB administration abolished REDs induced by 0-Mg 2+ solution, suggesting that CK2 inhibition indeed has anticonvulsive and perhaps antiepileptogenic properties. Significance: Our data demonstrated that CK2 inhibition augments the sAHP and might represent a novel mechanism of action of anticonvulsant drugs.

Differential contributions of Ca2+‐activated K+ channels and Na+/K+‐ATPases to the generation of the slow afterhyperpolarization in CA1 pyramidal cells

“…Because CA1 pyramidal cells are the main output channel from the hippocampus to the cortex (Witter, Wouterlood, Naber, & Van Haeften, ), their intrinsic excitability likely determines multiple brain functions. Indeed, changes in sAHP amplitude in these neurons have been implicated in learning and memory (Disterhoft, Wu, & Ohno, ; Brosh, Rosenblum, & Barkai, ; Zelcer et al, ; Zhang, Ouyang, Ganellin, & Thomas, ; Thomas, ), in cognitive decline in aging (Moyer, Power, Thompson, & Disterhoft, ; Disterhoft et al, ; Matthews, Linardakis, & Disterhoft, ) and in epileptogenesis (Brehme, Kirschstein, Schulz, & Köhling, ; Tamir, Daninos, & Yaari, ). Assuming an important role of ΝΚΑs in sAHP generation in vivo, it is very likely that these changes involve modulation of NKA activity through multiple signaling pathways (Ewart & Klip, ).…”

CK2 Inhibition Prior to Status Epilepticus Persistently Enhances KCa2 Function in CA1 Which Slows Down Disease Progression

“…Nonetheless, since pharmacological HCN channel inhibition by ZD7288 that does not distinguish between HCN isoforms led to an increase of sAHP-mediating currents (Gu et al, 2005), we propose that a net enhancement of HCN channel function by TBB could have antagonized an expected TBB-mediated sAHP increase due to enhanced K Ca 2 function. In fact, we previously found that the sAHP was increased in control and epileptic tissue when animals were pretreated in vivo with TBB (Brehme et al, 2014). On the one hand, this could be simply due to different recording procedures (isolated cells versus slice experiments) that differ with respect to recording from dendritic compartments expressing high levels of HCN1 (Nolan et al, 2004).…”

“…Only cells with an RMP of −50 mV or more negative were included in this study. The AHP-mediating K + current and charge transfer were measured in the voltage-clamp mode as previously described (Brehme et al, 2014). In brief, the recording solution contained 500 nM tetrodotoxin (TTX) and 1 mM tetraethylammonium (TEA) (both from Tocris Bioscience, Bristol, United Kingdom) to block voltage-activated Na + and K + channels, respectively.…”

“…Casein kinase 2 (CK2) is a widely expressed enzyme with a substantial number of possible targets; however, one of its major targets is calmodulin (CaM) and K Ca 2.2 (Bildl et al, 2004;Allen et al, 2007). We recently demonstrated that oral administration of the CK2 blocker 4,5,6,7-tetrabromotriazole (TBB) enhanced K + currents mediating the afterhyperpolarizing potential (AHP) in the pilocarpine model, and even more intriguing, blocked the occurrence of spontaneous epileptic activity in the acute slice model with Mg 2+ removal (Brehme et al, 2014). This compound obviously exerted an anti-epileptogenic potential in the in vitro slice preparation, but is not an anti-seizure drug in this model in vivo (Bajorat et al, 2018).…”

Potassium Channels in Epilepsy

“…Inhibiting SK channels leads to massive exacerbation of epileptiform activity in hippocampal slices of chronically epileptic rats but not in control tissue (Schulz et al 2012). Not only is the mAHP reduced in this tissue, but also the sAHP (Brehme et al 2014). The mAHP reduction can be restored by blocking casein-kinase 2 (CK2), a major kinase for calmodulin phosphorylation.…”