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Amiodarone reduces depolarization-evoked glutamate release from hippocampual synaptosomes

https://doi.org/10.1016/j.jphs.2017.02.014Get rights and content
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Abstract

Decreased brain glutamate level has emerged as a new therapeutic approach for epilepsy. This study investigated the effect and mechanism of amiodarone, an anti-arrhythmic drug with antiepileptic activity, on glutamate release in the rat hippocampus. In a synaptosomal preparation, amiodarone reduced 4-aminopyridine-evoked Ca2+-dependent glutamate release and cytosolic Ca2+ concentration elevation. Amiodarone did not affect the 4-aminopyridine-evoked depolarization of the synaptosomal membrane potential or the Na+ channel activator veratridine-evoked glutamate release, indicating that the amiodarone-mediated inhibition of glutamate release is not caused by a decrease in synaptosomal excitability. The inhibitory effect of amiodarone on 4-aminopyridine-evoked glutamate release was markedly decreased in synaptosomes pretreated with the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, the calmodulin antagonists W7 and calmidazolium, or the protein kinase A inhibitors H89 and KT5720. However, the intracellular Ca2+-release inhibitors dantrolene and CGP37157 had no effect on the amiodarone-mediated inhibition of glutamate release. Furthermore, amiodarone reduced the frequency of miniature excitatory postsynaptic currents without affecting their amplitude in hippocampal slices. Our data suggest that amiodarone reduces Ca2+ influx through N- and P/Q-type Ca2+ channels, subsequently reducing the Ca2+-calmodulin/protein kinase A cascade to inhibit the evoked glutamate release from rat hippocampal nerve terminals.

Keywords

Amiodarone
Glutamate release
Ca2+ channels
Synaptosomes
Hippocampus

Abbreviations

[Ca2+]C
cytosolic free Ca2+ concentration
DiSC3(5)
3′,3′,3′-dipropylthiadicarbocyanine iodide
DL-TBOA
DL-threo-beta-benzyl-oxy aspartate
Fura-2-AM
fura-2-acetoxymethyl ester
GDH
glutamate dehydrogenase
HBM
HEPES buffer medium
BSA
bovine serum albumin
CGP37157
7-chloro-5-(2-chloropheny)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one
H89
N-[2-(p-bromocinnamylamino)-ethyl]-5-isoquinolinesulfonamide dihydrochloride
KT5720
hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo-benzodiazocine-10-carboxylic acid
GF109203X
bisindolylmaleimide I
mEPSCs
miniature excitatory postsynaptic currents
CNQX
6-cyano-7-nitroquinoxaline-2,3-dione
D-AP5
D(-)-2-amino-5-phosphonopentanoic acid
CNS
central nervous system

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Peer review under responsibility of Japanese Pharmacological Society.