Sevoflurane potentiates and blocks GABA-induced currents through recombinant α1ß2γ2 GABAA receptors:: implications for an enhanced GABAergic transmission

Background and objective The gamma -aminobutyric acid(A), receptor (GABA(A)R) is a target for anaesthetic agents. We investigated the interactions of sevoflurane with a recombinant GABA(A)R. 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 alpha (1)beta (2)gamma (2) GABA(A)R 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 0.01mM 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 GABA(A)R, as suggested by the decreased current rise times. This explains the enhancement of the currents induced by low GABA concentrations (0.01mM). Additionally, sevoflurane (b) induces a picrotoxin-like open-channel block at the GABA(A)R. 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.