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: 9.67). 09/2009; 106(41):17546-51. DOI: 10.1073/pnas.0907228106
Source: PubMed


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.

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    • "The TASK-3 channel is also over expressed in a variety of cancers and confers hypoxia resistance on tumors (Mu et al., 2003). Knockout mice lacking one or both TASK channels display a variety of phenotypes including impaired carotid body chemosensing (Lopez-Barneo), sleep fragmentation (Pang et al., 2009), anti-depressive behavior (Gotter et al., This article has not been copyedited and formatted. The final version may differ from this version. "
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    ABSTRACT: PKTHPP, A1899, and doxapram are compounds that inhibit TASK-1 (KCNK3) and TASK-3 (KCNK9) tandem pore (K2P) potassium channel function and that stimulate breathing. To better understand the molecular mechanism(s) of action of these drugs, we undertook studies to identify amino acid residues in the TASK-3 protein that mediate this inhibition. Guided by homology modeling and molecular docking, we hypothesized PKTHPP and A1899 bind in the TASK-3 intracellular pore. To test our hypothesis, we mutated each residue in or near the predicted PKTHPP and A1899 binding site (residues 118 to 128 and 228 to 248), individually, to a negatively charged aspartate. We quantified each mutation's effect on TASK-3 potassium channel concentration-response to PKTHPP. Studies were conducted on TASK-3 transiently expressed in a Fischer rat thyroid epithelial monolayers; channel function was measured in an Ussing chamber. TASK-3 pore mutations at residues-122 (L122D, E, or K) and -236 (G236D) caused the IC50 of PKTHPP to increase more than 1000-fold. TASK-3 mutants L122D, G236D, L239D, and V242D were resistant to block by PKTHPP, A1899, and doxapram. Our data are consistent with a model in which breathing stimulant compounds PKTHPP, A1899, and doxapram inhibit TASK-3 function by binding at a common site within the channel intracellular pore region, although binding outside the channel pore can not yet be excluded. The American Society for Pharmacology and Experimental Therapeutics.
    Preview · Article · Aug 2015 · Molecular pharmacology
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    • "Studies with TASK-3-knockout mice confirmed the relevance of this channel. Compared with wildtype control mice, TASK-3-knockout mice require increased amounts of volatile anesthesia for loss of consciousness and immobility, are slower to lose consciousness, and, in the absence of anesthesia, display fragmented sleep (Pang et al., 2009; Lazarenko et al., 2010). "
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    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.
    Full-text · Article · Dec 2011 · Molecular pharmacology
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    • "Surprisingly, general anaesthesia—like sleep—is also a phenomenon that is ubiquitous in the animal kingdom. Why this should be so is unknown, but it would seem likely that general anaesthesia is—in part—a chemical hijacking of natural sleep mechanisms (Franks 2008; Pang et al. 2009). At the molecular level this would involve interactions with evolutionarily conserved protein ion channels and pumps that are necessary for homeostatic control of nervous system activity. "
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    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.
    Full-text · Chapter · Jul 2011
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