Dual actions of enflurane on postsynaptic currents abolished by the gamma-aminobutyric acid type A receptor beta3(N265M) point mutation.
BACKGROUND
At concentrations close to 1 minimum alveolar concentration (MAC)-immobility, volatile anesthetics display blocking and prolonging effects on gamma-aminobutyric acid type A receptor-mediated postsynaptic currents. It has been proposed that distinct molecular mechanisms underlie these dual actions. The authors investigated whether the blocking or the prolonging effect of enflurane is altered by a point mutation (N265M) in the beta3 subunit of the gamma-aminobutyric acid type A receptor. Furthermore, the role of the beta3 subunit in producing the depressant actions of enflurane on neocortical neurons was elucidated.


METHODS
Spontaneous inhibitory postsynaptic currents were sampled from neocortical neurons in cultured slices derived from wild-type and beta3(N265M) mutant mice. The effects of 0.3 and 0.6 mm enflurane on decay kinetics, peak amplitude, and charge transfer were quantified. Furthermore, the impact of enflurane-induced changes in spontaneous action potential firing was evaluated by extracellular recordings in slices from wild-type and mutant mice.


RESULTS
In slices derived from wild-type mice, enflurane prolonged inhibitory postsynaptic current decays and decreased peak amplitudes. Both effects were almost absent in slices from beta3(N265M) mutant mice. At clinically relevant concentrations between MAC-awake and MAC-immobility, the anesthetic was less effective in depressing spontaneous action potential firing in slices from beta3(N265M) mutant mice compared with wild-type mice.


CONCLUSIONS
At concentrations between MAC-awake and MAC-immobility, beta3-containing gamma-aminobutyric acid type A receptors contribute to the depressant actions of enflurane in the neocortex. The beta3(N265M) mutation affects both the prolonging and blocking effects of enflurane on gamma-aminobutyric acid type A receptor-mediated inhibitory postsynaptic currents in neocortical neurons.
Drexler
Berthold
B
Department of Anesthesiology, Experimental Anesthesiology Section, University of Tuebingen, Germany. berthold.drexler@uni-tuebingen.de
Jurd
Rachel
R
Rudolph
Uwe
U
Antkowiak
Bernd
B
D000200:Action Potentials / Q000187:drug effects; D000465:Algorithms; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000166:cytology / Q000187:drug effects; D002478:Cells, Cultured; D003627:Data Interpretation, Statistical; D003864:Depression, Chemical; D004594:Electrophysiology; D004737:Enflurane / Q000494:pharmacology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects*; D005260:Female; D008297:Male; D051379:Mice; D019579:Neocortex / Q000166:cytology / Q000187:drug effects; D009474:Neurons / Q000502:physiology; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D017354:Point Mutation / Q000502:physiology*; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000235:genetics*
D018685:Anesthetics, Inhalation; C546270:Gabrb3 protein, mouse; D011963:Receptors, GABA-A; D004737:Enflurane