Department of Anesthesiology

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Selective depression by general anesthetics of glutamate versus GABA release from isolated cortical nerve terminals.

TitleSelective depression by general anesthetics of glutamate versus GABA release from isolated cortical nerve terminals.
Publication TypeJournal Article
Year of Publication2003
AuthorsWestphalen RI, Hemmings HC
JournalJ Pharmacol Exp Ther
Volume304
Issue3
Pagination1188-96
Date Published2003 Mar
ISSN0022-3565
Keywords4-Aminopyridine, Anesthetics, General, Animals, gamma-Aminobutyric Acid, Glutamic Acid, Isoflurane, Male, Potassium, Rats, Rats, Sprague-Dawley, Synaptosomes
Abstract

The role of presynaptic mechanisms in general anesthetic depression of excitatory glutamatergic neurotransmission and facilitation of GABA-mediated inhibitory neurotransmission is unclear. A dual isotope method allowed simultaneous comparisons of the effects of a representative volatile (isoflurane) and intravenous (propofol) anesthetic on the release of glutamate and GABA from isolated rat cerebrocortical nerve terminals (synaptosomes). Synaptosomes were prelabeled with L-[(3)H]glutamate and [(14)C]GABA, and release was determined by superfusion with pulses of 30 mM K(+) or 1 mM 4-aminopyridine (4AP) in the absence or presence of 1.9 mM free Ca(2+). Isoflurane maximally inhibited Ca(2+)-dependent 4AP-evoked L-[(3)H]glutamate release (99 +/- 8% inhibition) to a greater extent than [(14)C]GABA release (74 +/- 6% inhibition; P = 0.023). Greater inhibition of L-[(3)H]glutamate versus [(14)C]GABA release was also observed for the Na(+) channel antagonists tetrodotoxin (99 +/- 4 versus 63 +/- 5% inhibition; P < 0.001) and riluzole (84 +/- 5 versus 52 +/- 12% inhibition; P = 0.041). Propofol did not differ in its maximum inhibition of Ca(2+)-dependent 4AP-evoked L-[(3)H]glutamate release (76 +/- 12% inhibition) compared with [(14)C]GABA (84 +/- 31% inhibition; P = 0.99) release. Neither isoflurane (1 mM) nor propofol (15 microM) affected K(+)-evoked release, consistent with a molecular target upstream of the synaptic vesicle exocytotic machinery or voltage-gated Ca(2+) channels coupled to transmitter release. These findings support selective presynaptic depression of excitatory versus inhibitory neurotransmission by clinical concentrations of isoflurane, probably as a result of Na(+) channel blockade.

DOI10.1124/jpet.102.044685
Alternate JournalJ. Pharmacol. Exp. Ther.
PubMed ID12604696
Grant ListGM 58055 / GM / NIGMS NIH HHS / United States