Neuronal preconditioning by inhalational anesthetics: evidence for the role of plasmalemmal adenosine triphosphate-sensitive potassium channels.
BACKGROUND
Ischemic preconditioning is an important intrinsic mechanism for neuroprotection. Preconditioning can also be achieved by exposure of neurons to K+ channel-opening drugs that act on adenosine triphosphate-sensitive K+ (K(ATP)) channels. However, these agents do not readily cross the blood-brain barrier. Inhalational anesthetics which easily partition into brain have been shown to precondition various tissues. Here, the authors explore the neuronal preconditioning effect of modern inhalational anesthetics and investigate their effects on K(ATP) channels.


METHODS
Neuronal-glial cocultures were exposed to inhalational anesthetics in a preconditioning paradigm, followed by oxygen-glucose deprivation. Increased cell survival due to preconditioning was quantified with the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide reduction test. Recombinant plasmalemmal K(ATP) channels of the main neuronal type (Kir6.2/SUR1) were expressed in HEK293 cells, and the effects of anesthetics were evaluated in whole cell patch clamp recordings.


RESULTS
Both sevoflurane and the noble gas xenon preconditioned neurons at clinically used concentrations. The effect of sevoflurane was independent of K(ATP) channel activation, whereas the effect of xenon required the opening of plasmalemmal K(ATP) channels. Recombinant K(ATP) channels were activated by xenon but inhibited by halogenated volatiles. Modulation of mitochondrial K-ATP channels did not affect the activity of K(ATP) channels, thus ruling out an indirect effect of volatiles via mitochondrial channels.


CONCLUSIONS
The preconditioning properties of halogenated volatiles cannot be explained by their effect on K(ATP) channels, whereas xenon preconditioning clearly involves the activation of these channels. Therefore, xenon might mimic the intrinsic mechanism of ischemic preconditioning most closely. This, together with its good safety profile, might suggest xenon as a viable neuroprotective agent in the clinical setting.
Department of Anaesthetics, Pain Medicine and Intensive Care, Chelsea and Westminster Hospital, Imperial College London, London, UK.
Carsten
C
Bantel
Mervyn
M
Maze
Stefan
S
Trapp
D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D006801:Humans; D054086:KATP Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000008:administration & dosage; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors / Q000502:physiology; D051381:Rats; D014978:Xenon / Q000008:administration & dosage; D000099161:Kcnj11 Channel
D018685:Anesthetics, Inhalation; D054086:KATP Channels; D026902:Potassium Channel Blockers; D024661:Potassium Channels, Inwardly Rectifying; D014978:Xenon; D000099161:Kcnj11 Channel