Abstract
Levetiracetam (LEV) is a prominent antiepileptic drug that binds to neuronal synaptic vesicle glycoprotein 2A protein and has reported effects on ion channels, but with a poorly defined mechanism of action. We investigated inhibition of voltage-dependent Ca2+ (CaV) channels as a potential mechanism through which LEV exerts effects on neuronal activity. We used electrophysiological methods to investigate the effects of LEV on cholinergic synaptic transmission and CaV channel activity in superior cervical ganglion neurons (SCGNs). In parallel, we investigated the effects of the inactive LEV R-enantiomer, (R)-α-ethyl-2-oxo-1-pyrrolidine acetamide (UCB L060). LEV but not UCB L060 (each at 100 μM) inhibited synaptic transmission between SCGNs in long-term culture in a time-dependent manner, significantly reducing excitatory postsynaptic potentials after a ≥30-min application. In isolated SCGNs, LEV pretreatment (≥1 h) but not short-term application (5 min) significantly inhibited whole-cell Ba2+ current (IBa) amplitude. In current-clamp recordings, LEV reduced the amplitude of the afterhyperpolarizing potential in a Ca2+-dependent manner but also increased the action potential latency in a Ca2+-independent manner, which suggests additional mechanisms associated with reduced excitability. Intracellular LEV application (4–5 min) caused rapid inhibition of IBa amplitude, to an extent comparable to that seen with extracellular LEV pretreatment (≥1 h). Neither pretreatment nor intracellular application of UCB L060 produced any inhibitory effects on IBa amplitude. These results identify a stereospecific intracellular pathway through which LEV inhibits presynaptic CaV channels; resultant reductions in neuronal excitability are proposed to contribute to the anticonvulsant effects of LEV.
Footnotes
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by a UCB Pharma investigator-initiated nonclinical study studentship award and a Japan Society for the Promotion of Science short-term fellowship.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- LEV
- levetiracetam
- AP
- action potential
- AED
- antiepileptic drug
- AHP
- afterhyperpolarizing potential
- CaV
- voltage-dependent Ca2+
- EPSP
- excitatory postsynaptic potential
- ECS
- extracellular solution
- IBa
- Ba2+ current
- KV
- voltage-dependent K+
- PBS
- phosphate-buffered saline
- PPP
- phase plane projection
- SCG
- superior cervical ganglion
- SCGN
- superior cervical ganglion neuron
- SV2A
- synaptic vesicle glycoprotein 2A
- UCB L060
- (R)-α-ethyl-2-oxo-1-pyrrolidine acetamide.
- Received November 4, 2011.
- Accepted May 3, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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