Volatile anesthetics inhibit sodium channels without altering bulk lipid bilayer properties.
Although general anesthetics are clinically important and widely used, their molecular mechanisms of action remain poorly understood. Volatile anesthetics such as isoflurane (ISO) are thought to alter neuronal function by depressing excitatory and facilitating inhibitory neurotransmission through direct interactions with specific protein targets, including voltage-gated sodium channels (Na(v)). Many anesthetics alter lipid bilayer properties, suggesting that ion channel function might also be altered indirectly through effects on the lipid bilayer. We compared the effects of ISO and of a series of fluorobenzene (FB) model volatile anesthetics on Na(v) function and lipid bilayer properties. We examined the effects of these agents on Na(v) in neuronal cells using whole-cell electrophysiology, and on lipid bilayer properties using a gramicidin-based fluorescence assay, which is a functional assay for detecting changes in lipid bilayer properties sensed by a bilayer-spanning ion channel. At clinically relevant concentrations (defined by the minimum alveolar concentration), both the FBs and ISO produced prepulse-dependent inhibition of Na(v) and shifted the voltage dependence of inactivation toward more hyperpolarized potentials without affecting lipid bilayer properties, as sensed by gramicidin channels. Only at supra-anesthetic (toxic) concentrations did ISO alter lipid bilayer properties. These results suggest that clinically relevant concentrations of volatile anesthetics alter Na(v) function through direct interactions with the channel protein with little, if any, contribution from changes in bulk lipid bilayer properties. Our findings further suggest that changes in lipid bilayer properties are not involved in clinical anesthesia.
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065 hchemmi@med.cornell.edu sparre@med.cornell.edu kah2016@med.cornell.edu.
Karl F
KF
Herold
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065.
R Lea
RL
Sanford
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065.
William
W
Lee
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065.
Margaret F
MF
Schultz
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065.
Helgi I
HI
Ingólfsson
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065 hchemmi@med.cornell.edu sparre@med.cornell.edu kah2016@med.cornell.edu.
Olaf S
OS
Andersen
Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065 Department of Anesthesiology, Department of Physiology and Biophysics, and Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065 hchemmi@med.cornell.edu sparre@med.cornell.edu kah2016@med.cornell.edu.
Hugh C
HC
Hemmings
D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005464:Fluorobenzenes; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007530:Isoflurane / Q000008:administration & dosage* / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D051379:Mice; D009474:Neurons; D012964:Sodium / Q000737:chemistry* / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000008:administration & dosage; D055549:Volatile Organic Compounds / Q000008:administration & dosage; D061566:Voltage-Gated Sodium Channels / Q000737:chemistry* / Q000502:physiology*
D018685:Anesthetics, Inhalation; D005464:Fluorobenzenes; D008051:Lipid Bilayers; D026941:Sodium Channel Blockers; D055549:Volatile Organic Compounds; D061566:Voltage-Gated Sodium Channels; D012964:Sodium; D007530:Isoflurane