title: Inhibition of neuronal Ca(2+) influx by gabapentin and subsequent reduction of neurotransmitter release from rat neocortical slices.
abstract: Cytosolic calcium ion concentrations ([Ca(2+)](i)) were measured in rat neocortical synaptosomes using fura-2, and depolarization of synaptosomal membranes was induced by K(+) (30 mM). The release of the endogenous excitatory amino acids glutamate and aspartate was evoked by K(+) (50 mM) and determined by HPLC. The release of [(3)H]-noradrenaline from rat neocortical synaptosomes or slices was evoked by K(+) (15 and 25 mM) and measured by liquid scintillation counting. Gabapentin produced a concentration-dependent inhibition of the K(+)-induced [Ca(2+)](i) increase in synaptosomes (IC(50)=14 microM; maximal inhibition by 36%). The inhibitory effect of gabapentin was abolished in the presence of the P/Q-type Ca(2+) channel blocker omega-agatoxin IVA, but not by the N-type Ca(2+) channel antagonist omega-conotoxin GVIA. Gabapentin (100 microM) decreased the K(+)-evoked release of endogenous aspartate and glutamate in neocortical slices by 16 and 18%, respectively. Gabapentin reduced the K(+)-evoked [(3)H]-noradrenaline release in neocortical slices (IC(50)=48 microM; maximal inhibition of 46%) but not from synaptosomes. In the presence of the AMPA receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2, 3-dioxo-6-nitro-1,2,3,4-tetrahydro[f]quinoxaline-7-sulphonamide (NBQX), gabapentin did not reduce [(3)H]-noradrenaline release. Gabapentin did, however, cause inhibition in the presence of the NMDA receptor antagonist DL-(E)-2-amino-4-methyl-5-phosphono-3-pentanoic acid (CGP 37849). Gabapentin is concluded to reduce the depolarization-induced [Ca(2+)](i) increase in excitatory amino acid nerve terminals by inhibiting P/Q-type Ca(2+) channels; this decreased Ca(2+) influx subsequently attenuates K(+)-evoked excitatory amino acid release. The latter effect leads to a reduced activation of AMPA receptors which contribute to K(+)-evoked noradrenaline release from noradrenergic varicosities, resulting in an indirect inhibition of noradrenaline release.
authors.affiliation: Department of Pharmacology and Toxicology, University of Bonn Medical School, Reuterstrasse 2b, 53113 Bonn, Germany. finkk@uni-bonn.de
authors.forename: K
authors.initials: K
authors.lastname: Fink
authors.forename: W
authors.initials: W
authors.lastname: Meder
authors.forename: D J
authors.initials: DJ
authors.lastname: Dooley
authors.forename: M
authors.initials: M
authors.lastname: Göthert
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000031:analogs & derivatives / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology*; D000588:Amines; D000818:Animals; D001224:Aspartic Acid / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003509:Cyclohexanecarboxylic Acids; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D000077206:Gabapentin; D005971:Glutamates / Q000187:drug effects / Q000378:metabolism; D008297:Male; D017072:Neostriatum / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014316:Tritium; D005680:gamma-Aminobutyric Acid; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
chemical_list: D000085:Acetates; D000588:Amines; D003509:Cyclohexanecarboxylic Acids; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D018377:Neurotransmitter Agents; D011810:Quinoxalines; D018091:Receptors, AMPA; D020867:omega-Agatoxin IVA; D014316:Tritium; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C064539:2-amino-4-methyl-5-phosphono-3-pentenoic acid; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D015763:2-Amino-5-phosphonovalerate; D020866:omega-Conotoxin GVIA; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine