Article

An unexpected role for TASK-3 potassium channels in network oscillations with implications for sleep mechanisms and anesthetic action

Biophysics Section, Blackett Laboratory, Imperial College, South Kensington, London SW7 2AZ, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 09/2009; 106(41):17546-51. DOI: 10.1073/pnas.0907228106
Source: PubMed

ABSTRACT TASK channels are acid-sensitive and anesthetic-activated members of the family of two-pore-domain potassium channels. We have made the surprising discovery that the genetic ablation of TASK-3 channels eliminates a specific type of theta oscillation in the cortical electroencephalogram (EEG) resembling type II theta (4-9 Hz), which is thought to be important in processing sensory stimuli before initiating motor activity. In contrast, ablation of TASK-1 channels has no effect on theta oscillations. Despite the absence of type II theta oscillations in the TASK-3 knockout (KO) mice, the related type I theta, which has certain neuronal pathways in common and is involved in exploratory behavior, is unaffected. In addition to the absence of type II theta oscillations, the TASK-3 KO animals show marked alterations in both anesthetic sensitivity and natural sleep behavior. Their sensitivity to halothane, a potent activator of TASK channels, is greatly reduced, whereas their sensitivity to cyclopropane, which does not activate TASK-3 channels, is unchanged. The TASK-3 KO animals exhibit a slower progression from their waking to sleeping states and, during their sleeping period, their sleep episodes as well as their REM theta oscillations are more fragmented. These results imply a previously unexpected role for TASK-3 channels in the cellular mechanisms underlying these behaviors and suggest that endogenous modulators of these channels may regulate theta oscillations.

Download full-text

Full-text

Available from: Daniel S Pang, Jul 05, 2015
0 Followers
 · 
97 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: TASK-3 (KCNK9) tandem-pore potassium channels provide a volatile anesthetic-activated and Gα(q) protein- and acidic pH-inhibited potassium conductance important in neuronal excitability. Met-159 of TASK-3 is essential for anesthetic activation and may contribute to the TASK-3 anesthetic binding site(s). We hypothesized that covalent occupancy of an anesthetic binding site would irreversibly activate TASK-3. We introduced a cysteine at residue 159 (M159C) and studied the rate and effect of Cys-159 modification by N-ethylmaleimide (NEM), a cysteine-selective alkylating agent. TASK-3 channels were transiently expressed in Fischer rat thyroid cells, and their function was studied in an Ussing chamber. NEM irreversibly activated M159C TASK-3, with minimal effects on wild-type TASK-3. NEM-modified M159C channels were resistant to inhibition by both acidic pH and active Gα(q) protein. M159C channels that were first inhibited by Gα(q) protein were more-slowly activated by NEM, which suggests protection of Cys-159, and similar results were observed with isoflurane activation of wild-type TASK-3. M159W and M159F TASK-3 mutants behaved like NEM-modified M159C channels, with increased basal currents and resistance to inhibition by active Gα(q) protein or acidic pH. TASK-3 wild-type/M159C dimers expressed as a single polypeptide demonstrated that modification of a single Cys-159 was sufficient for TASK-3 activation, and M159F/M159C and M159W/M159C dimers provided evidence for cross-talk between subunits. The data are consistent with residue 159 contributing to an anesthetic regulatory site or sites, and they suggest that volatile anesthetics, through perturbations at a single site, increase TASK-3 channel activity and disrupt its regulation by active Gα(q) protein, a determinant of central nervous system arousal and consciousness.
    Molecular pharmacology 12/2011; 81(3):393-400. DOI:10.1124/mol.111.076281 · 4.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A diverse range of modelling approaches have been applied to try and understand some of the neural mechanisms that underlie transitions between wake-sleep (and rapid-eye movement-to-slow-wave sleep) states. There is a strong evolutionary argument that general anaesthesia exists because it is a form of drug-induced harnessing of natural sleep mechanisms. The theoretical models tend to either describe specific interactions between various brain-stem nuclei; or at the other extreme, assume that sleep is a universal property of all neural assemblies, and therefore follow a thalamo-cortico-centric approach Using a general cortex-based mean field model we propose that: (1) Unconsciousness during natural slow wave sleep is caused by blockade of cortical connectivity; which is induced by increased gamma-amino-butyric acid(GABA)-ergic activity and diminished excitatory neuromodulators—and hence relative cortical hyperpolarization. (2) The sleeping subject can be woken because the normal homeostatic effects of arousal neuromodulators are able to depolarize the cortex, and switch off the GABAergic systems. (3) Sedative doses of GABAergic general anaesthetic drugs augment GABAergic systems which then inhibit excitatory neuromodulators and trigger a sleep-like state. However excessive nociceptive activation of the brainstem arousal systems is still able to depolarize the cortex and switch off the GABAergic systems. (4) Larger doses of GABAergic general anaesthetics cause an irreversible global increase in the total charge carried by the inhibitory post synaptic potential. This causes an increased negative feedback loop in the cortex, which is not able to be overcome by intrinsic neuronal currents, and hence the patient cannot be woken up even by the most extreme nociceptive stimuli—the definition of general anaesthesia.
    07/2011: pages 21-41;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: General anesthetics cause sedation, hypnosis, and immobilization via CNS mechanisms that remain incompletely understood; contributions of particular anesthetic targets in specific neural pathways remain largely unexplored. Among potential molecular targets for mediating anesthetic actions, members of the TASK subgroup [TASK-1 (K2P3.1) and TASK-3 (K2P9.1)] of background K(+) channels are appealing candidates since they are expressed in CNS sites relevant to anesthetic actions and activated by clinically relevant concentrations of inhaled anesthetics. Here, we used global and conditional TASK channel single and double subunit knock-out mice to demonstrate definitively that TASK channels account for motoneuronal, anesthetic-activated K(+) currents and to test their contributions to sedative, hypnotic, and immobilizing anesthetic actions. In motoneurons from all knock-out mice lines, TASK-like currents were reduced and cells were less sensitive to hyperpolarizing effects of halothane and isoflurane. In an immobilization assay, higher concentrations of both halothane and isoflurane were required to render TASK knock-out animals unresponsive to a tail pinch; in assays of sedation (loss of movement) and hypnosis (loss-of-righting reflex), TASK knock-out mice showed a modest decrease in sensitivity, and only for halothane. In conditional knock-out mice, with TASK channel deletion restricted to cholinergic neurons, immobilizing actions of the inhaled anesthetics and sedative effects of halothane were reduced to the same extent as in global knock-out lines. These data indicate that TASK channels in cholinergic neurons are molecular substrates for select actions of inhaled anesthetics; for immobilization, which is spinally mediated, these data implicate motoneurons as the likely neuronal substrates.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 06/2010; 30(22):7691-704. DOI:10.1523/JNEUROSCI.1655-10.2010 · 6.75 Impact Factor