Efeito do anestésico inalatório sevoflurano na liberação de GABA em fatias de córtex cerebral de ratos

Abstract

The introduction of ether in anesthesia, by William Morton in 1846, and the emergence of other anesthetics made possible the development and improvement of different surgical modalities. However, despite the importance and the broad clinical use, the action mechanism of these agents is still unclear. Evidences show that anesthetics potentialize inhibitory neurotransmission, but the precise molecular targets remain unknown. The present study aimed to evaluate the effect of the inhalatory anesthetic sevoflurane on the release of GABA which is the main inhibitory neurotransmitter in mammalian central nervous system. Rat cortical brain slices were stained with [3H]GABA. Following centrifugation and washing out steps, slices were stimulated with different concentrations of anesthetic (0.058, 0.11, 0.23, 0.46, 0.93 mM). Sevoflurane increased [3H]GABA release in cortical brain slices. This effect was dose-dependent and time incubation-dependent. Such release was independent of Ca2+, since it was unaffected by EGTA and BAPTA. Inhibition of tetrodotoxin resistant Na+ channels didnt interfere on anesthetic induced [3H]GABA release as well. These data suggest that exocytotic [3H]GABA release is not related to sevoflurane action. SKF 89976A, a blocker of GAT1, a GABA transporter present at the pre-synaptic plasma membrane of GABAergic neurons, inhibited by 57,2% the sevoflurane induced GABA release (P<0,05). In the same way, it was observed an inhibition of 83,1% (p<0,05) in the sevoflurane induced GABA release when slices were kept at low temperatures (17oC). In this condition, GABA release mediated by carriers is impaired. -alanine, an inhibitor of GAT-2 and GAT-3 present at glial membranes, didnt interfere in the [3H]GABA release induced by the anesthetic, demonstrating that these cells seem not to be involved in that action. Altogether, results of the present work suggest that sevoflurane induces a non-exocytotic GABA release in rat brain cortical slices, through a calcium-independent way, that involves the transporter of this neurotransmitter, present at neuronal membrane