M-current preservation contributes to anticonvulsant effects of valproic acid
Hee Yeon Kay, … , Anastasia Kosenko, Naoto Hoshi
Hee Yeon Kay, … , Anastasia Kosenko, Naoto Hoshi
Published September 8, 2015
Citation Information: J Clin Invest. 2015;125(10):3904-3914. https://doi.org/10.1172/JCI79727.
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Research Article Neuroscience

M-current preservation contributes to anticonvulsant effects of valproic acid

Abstract

Valproic acid (VPA) has been widely used for decades to treat epilepsy; however, its mechanism of action remains poorly understood. Here, we report that the anticonvulsant effects of nonacute VPA treatment involve preservation of the M-current, a low-threshold noninactivating potassium current, during seizures. In a wide variety of neurons, activation of Gq-coupled receptors, such as the m1 muscarinic acetylcholine receptor, suppresses the M-current and induces hyperexcitability. We demonstrated that VPA treatment disrupts muscarinic suppression of the M-current and prevents resultant agonist-induced neuronal hyperexcitability. We also determined that VPA treatment interferes with M-channel signaling by inhibiting palmitoylation of a signaling scaffold protein, AKAP79/150, in cultured neurons. In a kainate-induced murine seizure model, administration of a dose of an M-channel inhibitor that did not affect kainate-induced seizure transiently eliminated the anticonvulsant effects of VPA. Retigabine, an M-channel opener that does not open receptor-suppressed M-channels, provided anticonvulsant effects only when administered prior to seizure induction in control animals. In contrast, treatment of VPA-treated mice with retigabine induced anticonvulsant effects even when administered after seizure induction. Together, these results suggest that receptor-induced M-current suppression plays a role in the pathophysiology of seizures and that preservation of the M-current during seizures has potential as an effective therapeutic strategy.

Authors

Hee Yeon Kay, Derek L. Greene, Seungwoo Kang, Anastasia Kosenko, Naoto Hoshi

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Figure 6

VPA selectively reduced palmitoylation of AKAP150 and several neuronal proteins.

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VPA selectively reduced palmitoylation of AKAP150 and several neuronal p...
(A) Palmitoylation of AKAP150 was evaluated using cultured hippocampal neurons. After ABE labeling, AKAP150 protein was purified by IP using monoclonal anti-AKAP150 antibody. Palmitoylation was detected by NeutrAvidin-HRP (upper panel). Middle panel shows equal recovery of AKAP150 among treatments assessed by immunoblots using rabbit anti-AKAP150 antibody. Bottom histogram shows summary of 3 independent experiments. Palmitoylation of AKAP150 was reduced in VPA-treated neurons. Requirement of NH2OH for biotinylation verified selective labeling of palmitoylation. *P < 0.05 using paired t test to control. (B) VPA treatment had minimal effect on overall palmitoylation in cultured hippocampal neuronal lysates. (C) ABE labeling was performed on mouse brain extracts, followed by purification of labeled proteins by NeutrAvidin-beads. Palmitoylation of indicated neural proteins was assessed by immunoblotting. VPA reduced palmitoylation of several but not all neuronal proteins. *P < 0.05 and **P < 0.01 using paired t test to control. Error bars show ± SEM. Numbers above bars represent n.