title: Isoflurane inhibits NaChBac, a prokaryotic voltage-gated sodium channel.
abstract: Volatile anesthetics inhibit mammalian voltage-gated Na(+) channels, an action that contributes to their presynaptic inhibition of neurotransmitter release. We measured the effects of isoflurane, a prototypical halogenated ether volatile anesthetic, on the prokaryotic voltage-gated Na(+) channel from Bacillus halodurans (NaChBac). Using whole-cell patch-clamp recording, human embryonic kidney 293 cells transfected with NaChBac displayed large inward currents (I(Na)) that activated at potentials of -60 mV or higher with a peak voltage of activation of 0 mV (from a holding potential of -80 mV) or -10 mV (from a holding potential of -100 mV). Isoflurane inhibited I(Na) in a concentration-dependent manner over a clinically relevant concentration range; inhibition was significantly more potent from a holding potential of -80 mV (IC(50) = 0.35 mM) than from -100 mV (IC(50) = 0.48 mM). Isoflurane positively shifted the voltage dependence of peak activation, and it negatively shifted the voltage dependence of end steady-state activation. The voltage dependence of inactivation was negatively shifted with no change in slope factor. Enhanced inactivation of I(Na) was 8-fold more sensitive to isoflurane than reduction of channel opening. In addition to tonic block of closed and/or open channels, isoflurane enhanced use-dependent block by delaying recovery from inactivation. These results indicate that a prokaryotic voltage-gated Na(+) channel, like mammalian voltage-gated Na(+) channels, is inhibited by clinical concentrations of isoflurane involving multiple state-dependent mechanisms. NaChBac should provide a useful model for structure-function studies of volatile anesthetic actions on voltage-gated ion channels.
authors.affiliation: Department of Anesthesiology, Weill Cornell Medical College, Box 50, LC-203, 525 E. 68th St., New York, NY 10065-4896, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Ouyang
authors.forename: Ting-Yu
authors.initials: TY
authors.lastname: Jih
authors.forename: Tao-Tao
authors.initials: TT
authors.lastname: Zhang
authors.forename: Ana M
authors.initials: AM
authors.lastname: Correa
authors.forename: Hugh C
authors.initials: HC
authors.lastname: Hemmings
mesh_terms: D018685:Anesthetics, Inhalation / Q000494:pharmacology; D001407:Bacillus / Q000737:chemistry; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D020128:Inhibitory Concentration 50; D015640:Ion Channel Gating / Q000187:drug effects*; D007530:Isoflurane / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000235:genetics; D014162:Transfection
chemical_list: D018685:Anesthetics, Inhalation; D001426:Bacterial Proteins; C443666:NaChBac protein, bacteria; D015222:Sodium Channels; D007530:Isoflurane