Sevoflurane potentiates and blocks GABA-induced currents through recombinant alpha1beta2gamma2 GABAA receptors: implications for an enhanced GABAergic transmission.
OBJECTIVE
The gamma-aminobutyric acidA receptor (GABAAR) is a target for anaesthetic agents. We investigated the interactions of sevoflurane with a recombinant GABAAR. Emphasis was on the mechanism of block, as relevant open-channel block by a volatile anaesthetic would possibly explain prolonged GABAergic postsynaptic currents.


METHODS
The effect of sevoflurane on GABA-induced currents through recombinant alpha1beta2gamma2 GABAAR channels was studied (patch clamp; HEK293 cells). GABA 0.01 mM or 1 mM was applied alone or together with sevoflurane (0.05 mM to 5 mM).


RESULTS
Currents elicited by GABA 0.01 mM were increased by low sevoflurane concentrations to 183% and decreased by high sevoflurane concentrations (> 1 mM) to 34% (P < 0.05). Ten- to 90%-rise times of the currents were reduced by sevoflurane concentration dependently. At GABA (1 mM), peak currents and 10-90%-rise times decreased with increasing sevoflurane concentrations. A transient current increase was induced by discontinuation of GABA and sevoflurane. Such rebound currents indicate a reversal of an open-channel block by sevoflurane.


CONCLUSIONS
Sevoflurane (a) increases the apparent affinity of GABA to the GABAAR, as suggested by the decreased current rise times. This explains the enhancement of the currents induced by low GABA concentrations (0.01 mM). Additionally, sevoflurane (b) induces a picrotoxin-like open-channel block at the GABAAR. The reversal of the open-channel block elicits a delayed GABA response. These findings indicate at least two different sites of action of sevoflurane at this receptor that are both important for an enhanced GABAergic synaptic transmission.
Hapfelmeier
G
G
Department of Anaesthesiology, Technische Universität München, Germany.
Schneck
H
H
Kochs
E
E
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D001640:Bicuculline / Q000494:pharmacology; D002460:Cell Line; D018756:GABA Antagonists / Q000494:pharmacology*; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008738:Methyl Ethers / Q000494:pharmacology*; D010852:Picrotoxin / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D000077149:Sevoflurane; D009435:Synaptic Transmission / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D018685:Anesthetics, Inhalation; D001640:Bicuculline; D018756:GABA Antagonists; D007473:Ion Channels; D008738:Methyl Ethers; D010852:Picrotoxin; D011963:Receptors, GABA-A; D000077149:Sevoflurane; D005680:gamma-Aminobutyric Acid