The tandem of pore domain in a weak inwardly rectifying K⁺ channel (Twik)-related acid-arachidonic activated K⁺ channel (TRAAK) and Twik-related K⁺ channels (TREK) 1 and TREK2 are active as ...homodimers gated by stretch, fatty acids, pH, and G protein-coupled receptors. These two-pore domain potassium (K2P) channels are broadly expressed in the nervous system where they control excitability. TREK/TRAAK KO mice display altered phenotypes related to nociception, neuroprotection afforded by polyunsaturated fatty acids, learning and memory, mood control, and sensitivity to general anesthetics. These channels have emerged as promising targets for the development of new classes of anesthetics, analgesics, antidepressants, neuroprotective agents, and drugs against addiction. Here, we show that the TREK1, TREK2, and TRAAK subunits assemble and form active heterodimeric channels with electrophysiological, regulatory, and pharmacological properties different from those of homodimeric channels. Heteromerization occurs between all TREK variants produced by alternative splicing and alternative translation initiation. These results unveil a previously unexpected diversity of K2P channels that will be challenging to analyze in vivo, but which opens new perspectives for the development of clinically relevant drugs.
Mutations that modulate the activity of ion channels are essential tools to understand the biophysical determinants that control their gating. Here, we reveal the conserved role played by a single ...amino acid position (TM2.6) located in the second transmembrane domain of two-pore domain potassium (K2P) channels. Mutations of TM2.6 to aspartate or asparagine increase channel activity for all vertebrate K2P channels. Using two-electrode voltage-clamp and single-channel recording techniques, we find that mutation of TM2.6 promotes channel gating via the selectivity filter gate and increases single channel open probability. Furthermore, channel gating can be progressively tuned by using different amino acid substitutions. Finally, we show that the role of TM2.6 was conserved during evolution by rationally designing gain-of-function mutations in four Caenorhabditis elegans K2P channels using CRISPR/Cas9 gene editing. This study thus describes a simple and powerful strategy to systematically manipulate the activity of an entire family of potassium channels.
The TWIK-related K
channel, TREK-1, has recently emerged as an attractive therapeutic target for the development of a novel class of analgesic drugs, suggesting that activation of TREK-1 could result ...in pain inhibition. Here, we report the synthesis of a series of substituted acrylic acids (1-54) based on our previous work with caffeate esters. The analogues were evaluated for their ability to modulate TREK-1 channel by electrophysiology and for their in vivo antinociceptive activity (acetic acid-induced writhing and hot plate assays), leading to the identification of a series of novel molecules able to activate TREK-1 and displaying potent antinociceptive activity in vivo. Furyl analogue 36 is the most promising of the series.
Recombinant TWIK2 channels produce weak basal background K
currents. Current amplitudes depend on the animal species the channels have been isolated from and on the heterologous system used for their ...re-expression. Here we show that this variability is due to a unique cellular trafficking. We identified three different sequence signals responsible for the preferential expression of TWIK2 in the Lamp1-positive lysosomal compartment. Sequential inactivation of tyrosine-based (Y
ASIP) and di-leucine-like (E
LILL and D
EDDQVDIL) trafficking motifs progressively abolishes the targeting of TWIK2 to lysosomes, and promotes its functional relocation at the plasma membrane. In addition, TWIK2 contains two N-glycosylation sites (N
AS and N
AS) on its luminal side, and glycosylation is necessary for expression in lysosomes. As shown by electrophysiology and electron microscopy, TWIK2 produces functional background K
currents in the endolysosomes, and its expression affects the number and mean size of the lysosomes. These results show that TWIK2 is expressed in lysosomes, further expanding the registry of ion channels expressed in these organelles.
TREK/TRAAK channels are polymodal K
channels that convert very diverse stimuli, including bioactive lipids, mechanical stretch and temperature, into electrical signals. The nature of the structural ...changes that regulate their activity remains an open question. Here, we show that a cytoplasmic domain (the proximal C-ter domain, pCt) exerts antagonistic effects in TREK1 and TRAAK. In basal conditions, pCt favors activity in TREK1 whereas it impairs TRAAK activity. Using the conformation-dependent binding of fluoxetine, we show that TREK1 and TRAAK conformations at rest are different, and under the influence of pCt. Finally, we show that depleting PIP
in live cells has a more pronounced inhibitory effect on TREK1 than on TRAAK. This differential regulation of TREK1 and TRAAK is related to a previously unrecognized PIP
-binding site (R329, R330, and R331) present within TREK1 pCt, but not in TRAAK pCt. Collectively, these new data point out pCt as a major regulatory domain of these channels and suggest that the binding of PIP
to the pCt of TREK1 results in the stabilization of the conductive conformation in basal conditions.
Alteration in the control of bone morphogenetic protein (BMP)-regulated genes and increased expression of endothelin (ET)-1 are both believed to play important roles in the still incompletely ...understood pathobiology of pulmonary vascular remodeling and fibrosis. Recent studies have drawn attention to the contribution of adventitial fibroblast activation in these phenomena. Because chloride channels are involved in the control of physiological function of fibroblasts, we hypothesized that these channels are differentially regulated by BMPs and ET. We measured chloride ion currents by whole-cell path-clamping in cultured primary human pulmonary fibroblasts. The application of BMP2 prevented activation of these currents by hypotonic challenge in a time- and dose-dependent manner, partially via protein kinase C signaling. Maximal inhibition was observed after 45-minute incubation of cells in the presence of 10 ng/ml of BMP2. ET-1 did not activate chloride channels acutely; however, prolonged treatment of cells with ET-1 (100 nM, 2 h) induced the appearance of lysophosphatidic acid-activated chloride currents (a marker of differentiated myofibroblasts), and this induction could be effectively blocked by BMP2 pretreatment (10 ng/ml). BMP2 also prevented stimulation of α-smooth muscle actin gene expression and cell migration of fibroblasts induced by ET-1. We conclude that ET-1 and BMP2 have opposing effects on chloride channel activity in human fibroblasts. This is a potentially relevant mechanism involved in pulmonary vascular remodeling and fibrosis.
Melatonin has been reported to present with vasorelaxant and anti-fibrotic properties. We hypothesized that melatonin may down-regulate volume-regulated anion channels (VRAC) in fibroblasts to limit ...their migration and proliferation. While acute exposure of L929 fibroblasts to melatonin did not result in a significant decrease in VRAC current, pretreatment with 100 μM melatonin for 1 h decreased swelling-dependent activation of anion currents by 83 % as measured by whole-cell perforated patch-clamp technique. This down-regulation of VRAC currents was dose-dependent with a half-maximal inhibition of 3.02 ± 0.48 μM. Overnight treatment of cells with 100 nM melatonin had the same inhibitory potency as a 1-h treatment with 100 μM. A similar down-regulatory effect of melatonin on VRAC was observed in primary rat lung fibroblasts. The effect of melatonin was prevented by luzindole and K185 that suggests implication of MT2 receptor. GF109203X, a protein kinase C inhibitor, blocked melatonin’s action on VRAC, indicating that MT2 receptor activation results in stimulation of PKC. Consequently, melatonin inhibited regulatory volume decrease following hypotonic swelling of cells. Melatonin also decreased the migration of L929 fibroblasts through the same pathways that blocked VRAC. There was no significant inhibition of cell proliferation. Our study suggests that the attenuation of fibrosis and vascular remodeling by melatonin seen in animal models of hypertension and pulmonary fibrosis might be, in part, related to blunted fibroblast migration possibly through protein kinase C-mediated decrease in chloride channel activity.
Background and Purpose
Opioids are effective painkillers. However, their risk–benefit ratio is dampened by numerous adverse effects and opioid misuse has led to a public health crisis. Safer ...alternatives are required, but isolating the antinociceptive effect of opioids from their adverse effects is a pharmacological challenge because activation of the μ opioid receptor triggers both the antinociceptive and adverse effects of opioids.
Experimental Approach
The TREK1 potassium channel is activated downstream of μ receptor and involved in the antinociceptive activity of morphine but not in its adverse effects. Bypassing the μ opioid receptor to directly activate TREK1 could therefore be a safer analgesic strategy.
Key Results
We developed a selective TREK1 activator, RNE28, with antinociceptive activity in naive rodents and in models of inflammatory and neuropathic pain. This activity was lost in TREK1 knockout mice or wild‐type mice treated with the TREK1 blocker spadin, showing that TREK1 is required for the antinociceptive activity of RNE28. RNE28 did not induce respiratory depression, constipation, rewarding effects, or sedation at the analgesic doses tested.
Conclusion and Implications
This proof‐of‐concept study shows that TREK1 activators could constitute a novel class of painkillers, inspired by the mechanism of action of opioids but devoid of their adverse effects.
Inhibitory potassium channels of the TREK1/TRAAK family are integrators of multiple stimuli, including temperature, membrane stretch, polyunsaturated fatty acids and pH. How these signals affect the ...gating of these channels is the subject of intense research. We have previously identified a cytoplasmic domain, pCt, which plays a major role in controlling channel activity. Here, we use pharmacology to show that the effects of pCt, arachidonic acid, and extracellular pH converge to the same gate within the channel. Using a state-dependent inhibitor, fluoxetine, as well as natural and synthetic openers, we provide further evidence that the “up” and “down” conformations identified by crystallography do not correspond to open and closed states of these channels.
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