|Title||Activity-dependent depression of neuronal sodium channels by the general anaesthetic isoflurane.|
|Publication Type||Journal Article|
|Year of Publication||2015|
|Authors||Purtell K, Gingrich KJ, OuYang W, Herold KF, Hemmings HC|
|Journal||Br J Anaesth|
|Date Published||2015 Jul|
|Keywords||Anesthesia, General, Anesthetics, Inhalation, Animals, Cells, Cultured, Isoflurane, Membrane Potentials, Neurons, Rats, Sodium Channels|
BACKGROUND: The mechanisms by which volatile anaesthetics such as isoflurane alter neuronal function are poorly understood, in particular their presynaptic mechanisms. Presynaptic voltage-gated sodium channels (Na(v)) have been implicated as a target for anaesthetic inhibition of neurotransmitter release. We hypothesize that state-dependent interactions of isoflurane with Na(v) lead to increased inhibition of Na(+) current (I(Na)) during periods of high-frequency neuronal activity.
METHODS: The electrophysiological effects of isoflurane, at concentrations equivalent to those used clinically, were measured on recombinant brain-type Na(v)1.2 expressed in ND7/23 neuroblastoma cells and on endogenous Na(v) in isolated rat neurohypophysial nerve terminals. Rate constants determined from experiments on the recombinant channel were used in a simple model of Na(v) gating.
RESULTS: At resting membrane potentials, isoflurane depressed peak I(Na) and shifted steady-state inactivation in a hyperpolarizing direction. After membrane depolarization, isoflurane accelerated entry (τ(control)=0.36 [0.03] ms compared with τ(isoflurane)=0.33 [0.05] ms, P<0.05) and slowed recovery (τ(control)=6.9 [1.1] ms compared with τ(isoflurane)=9.0 [1.9] ms, P<0.005) from apparent fast inactivation, resulting in enhanced depression of I(Na), during high-frequency stimulation of both recombinant and endogenous nerve terminal Na(v). A simple model of Na(v) gating involving stabilisation of fast inactivation, accounts for this novel form of activity-dependent block.
CONCLUSIONS: Isoflurane stabilises the fast-inactivated state of neuronal Na(v) leading to greater depression of I(Na) during high-frequency stimulation, consistent with enhanced inhibition of fast firing neurones.
|Alternate Journal||Br J Anaesth|
|PubMed Central ID||PMC4471819|
|Grant List||GM58055 / GM / NIGMS NIH HHS / United States |
GM58055S1 / GM / NIGMS NIH HHS / United States