Biophysical and Pharmacological Characteristics of Native Two-Pore Domain TASK Channels in Rat Adrenal Glomerulosa Cells

2006 ◽  
Vol 210 (1) ◽  
pp. 51-70 ◽  
Author(s):  
David P. Lotshaw
Keyword(s):  
Task Channels ◽  
Glomerulosa Cells ◽  
Pore Domain

Inhibition of TASK-1 potassium channel by phospholipase C

2001 ◽  
Vol 281 (2) ◽  
pp. C700-C708 ◽  
Author(s):  
Gábor Czirják ◽  
Gábor L. Petheő ◽  
András Spät ◽  
Péter Enyedi
Keyword(s):  
Phospholipase C ◽  
Lysophosphatidic Acid ◽  
Protein S ◽  
Receptor Activation ◽  
Xenopus Laevis Oocytes ◽  
Ang Ii ◽  
Inositol 1,4,5 Trisphosphate ◽  
Glomerulosa Cells ◽  
Pore Domain ◽  
Stimulation Of

The two-pore-domain K+ channel, TASK-1, was recently shown to be a target of receptor-mediated regulation in neurons and in adrenal glomerulosa cells. Here, we demonstrate that TASK-1 expressed in Xenopus laevis oocytes is inhibited by different Ca2+-mobilizing agonists. Lysophosphatidic acid, via its endogenous receptor, and ANG II and carbachol, via their heterologously expressed ANG II type 1a and M1 muscarinic receptors, respectively, inhibit TASK-1. This effect can be mimicked by guanosine 5′- O-(3-thiotriphosphate), indicating the involvement of GTP-binding protein(s). The phospholipase C inhibitor U-73122 reduced the receptor-mediated inhibition of TASK-1. Downstream signals of phospholipase C action (inositol 1,4,5-trisphosphate, cytoplasmic Ca2+ concentration, and diacylglycerol) do not mediate the inhibition. Unlike the Gq-coupled receptors, stimulation of the Gi-activating M2 muscarinic receptor coexpressed with TASK-1 results in an only minimal decrease of the TASK-1 current. However, additional coexpression of phospholipase C-β2 (which is responsive also to Giβγ-subunits) renders M2 receptor activation effective. This indicates the significance of phospholipase C activity in the receptor-mediated inhibition of TASK-1.

Gating of two-pore domain K+ channels by extracellular pH

2006 ◽  
Vol 34 (5) ◽  
pp. 899-902 ◽  
Author(s):  
M.I. Niemeyer ◽  
F.D. González-Nilo ◽  
L. Zúñiga ◽  
W. González ◽  
L.P. Cid ◽  
...  
Keyword(s):  
Extracellular Ph ◽  
Selectivity Filter ◽  
Open Probability ◽  
K Channels ◽  
Task Channels ◽  
Pore Mouth ◽  
Inactivation Gating ◽  
Opening And Closing ◽  
Pore Domain ◽  
And Task

Potassium channels have a conserved selectivity filter that is important in determining which ions are conducted and at what rate. Although K+ channels of different conductance characteristics are known, they differ more widely in the way their opening and closing, the gating, is governed. TASK and TALK subfamily proteins are two-pore region KCNK K+ channels gated open by extracellular pH. We discuss the mechanism for this gating in terms of electrostatic effects on the pore changing the occupancy and open probability of the channels in a way reminiscent of C-type inactivation gating at the selectivity filter. Essential to this proposed mechanism is the replacement of two highly conserved aspartate residues at the pore mouth by asparagine or histidine residues in the TALK and TASK channels.

scholarly journals A unique lower X-gate in TASK channels traps inhibitors within the vestibule

2019 ◽  
Author(s):  
Karin E. J. Rödström ◽  
Aytuğ K. Kiper ◽  
Wei Zhang ◽  
Susanne Rinné ◽  
Ashley C. W. Pike ◽  
...  
Keyword(s):  
Potassium Channels ◽  
Selectivity Filter ◽  
Resting Membrane Potential ◽  
Transmembrane Helices ◽  
Volatile Anaesthetics ◽  
Open Probability ◽  
High Affinity ◽  
Obstructive Sleep ◽  
Task Channels ◽  
Pore Domain

TASK channels are unusual members of the two-pore domain potassium (K2P) channel family, with unique and unexplained physiological and pharmacological characteristics. TASKs are found in neurons1,2, cardiomyocytes3–5 and vascular smooth muscle cells6 where they are involved in regulation of heart rate7, pulmonary artery tone6,8, sleep/wake cycles9 and responses to volatile anaesthetics9–12. K2P channels regulate the resting membrane potential, providing background K+ currents controlled by numerous physiological stimuli13,14. Unlike other K2P channels, TASK channels have the capacity to bind inhibitors with high affinity, exceptional selectivity and very slow compound washout rates. These characteristics make the TASK channels some of the the most easily druggable potassium channels, and indeed TASK-1 inhibitors are currently in clinical trials for obstructive sleep apnea (OSA) and atrial fibrillation (Afib)15 (The DOCTOS and SANDMAN Trials). Generally, potassium channels have an intramembrane vestibule with a selectivity filter above and a gate with four parallel helices below. However, K2P channels studied to date all lack a lower gate. Here we present the structure of TASK-1, revealing a unique lower gate created by interaction of the two crossed C-terminal M4 transmembrane helices at the vestibule entrance, which we designate as an ‟X-gate”. This structure is formed by six residues (V243LRFMT248) that are essential for responses to volatile anaesthetics11, neuro-transmitters16 and G-protein coupled receptors16. Interestingly, mutations within the X-gate and surrounding regions drastically affect both open probability and activation by anaesthetics. Structures of TASK-1 with two novel, high-affinity blockers, shows both inhibitors bound below the selectivity filter, trapped in the vestibule by the X-gate, thus explaining their exceptionally low wash-out rates. Thus, the presence of the X-gate in TASK channels explains many aspects of their unusual physiological and pharmacological behaviour, which is invaluable for future development and optimization of TASK modulators for treatment of heart, lung and sleep disorders.

269 EXPRESSION OF TANDEM-PORE DOMAIN K+ CHANNELS IN BOVINE OOCYTES AND PRE-IMPLANTATION EMBRYOS

2007 ◽  
Vol 19 (1) ◽  
pp. 251
Author(s):  
C. G. Hur ◽  
D. Kang ◽  
J. Y. Park ◽  
S. G. Hong ◽  
J. Han
Keyword(s):  
Germinal Vesicle ◽  
Human Myometrium ◽  
Resting Membrane Potential ◽  
Rt Pcr ◽  
Cellular Functions ◽  
Cell Stage ◽  
K Channels ◽  
Task Channels ◽  
Pore Domain ◽  
Bovine Oocytes

Tandem-pore domain K+ (K2P) channels that contribute to setting the resting membrane potential of excitable and nonexcitable cells are expressed in many kinds of cells and tissues. Recent studies have shown that TASK [TWIK (Tandem of P domains in Weak Inward rectifying K+ channels)-related acid-sensitive K+ channels] and TREK (TWIK-Related K+ channels), members of K2P channel family that are involved in a variety of cellular functions, are expressed in human myometrium, placenta, and cytotrophoblast cells. However, their expression in bovine oocytes and embryos has not yet been reported. In this study, we examined whether TASK and TREK channels are expressed in bovine immature (germinal vesicle-stage) and mature (metaphase II-stage) oocytes and in pre-implantation (2-cell- and 16-cell-stage) embryos using RT-PCR and immunocytochemistry. RT-PCR data showed that TASK-1, TASK-3, TREK-1, TREK-2, and TRAAK channels were expressed in bovine immature and mature oocytes. Interestingly, the expression levels of TREK channels were 2-fold higher than those of TASK channels as judged by semiquantitative RT-PCR and real-time PCR with cDNA synthesized from 50 individual immature and mature oocytes (P < 0.05, n = 4). Intensity of genes was normalized with respect to that of GAPDH. Consistent with RT-PCR data, immunocytochemical data showed that TASK-1, TASK-3, TREK-1, TREK-2, and TRAAK channels were expressed in bovine immature and mature oocytes. The fluorescence intensity of TREK channels was higher than that of TASK channels (P < 0.05, n = 5). TASK and TREK channels were also expressed in pre-implantation embryos. Of TREK channels, the TREK-2 channel was strongly expressed in immature and mature oocytes and in pre-implantation embryos (P < 0.05, n = 5). For statistics, Student's t-test was used, with P < 0.05 as the criterion for significance. Our results show that TASK-1, TASK-3, TREK-1, TREK-2, and TRAAK channels were expressed in bovine immature and mature oocytes and pre-implantation embryos. These results suggest that TASK and TREK channels could be involved in various physiological processes in mammalian oocytes and embryos.

scholarly journals A “Target Class” Screen to Identify Activators of Two-Pore Domain Potassium (K2P) Channels

2020 ◽  
pp. 247255522097612
Author(s):  
David McCoull ◽  
Emma Ococks ◽  
Jonathan M. Large ◽  
David C. Tickle ◽  
Alistair Mathie ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Point Of View ◽  
Resting Membrane Potential ◽  
Small Molecule Activation ◽  
Target Class ◽  
Index Set ◽  
Diverse Range ◽  
K2p Channels ◽  
Additional Approach ◽  
Pore Domain

Two-pore domain potassium (K2P) channels carry background (or leak) potassium current and play a key role in regulating resting membrane potential and cellular excitability. Accumulating evidence points to a role for K2Ps in human pathophysiologies, most notably in pain and migraine, making them attractive targets for therapeutic intervention. However, there remains a lack of selective pharmacological tools. The aim of this work was to apply a “target class” approach to investigate the K2P superfamily and identify novel activators across all the described subclasses of K2P channels. Target class drug discovery allows for the leveraging of accumulated knowledge and maximizing synergies across a family of targets and serves as an additional approach to standard target-based screening. A common assay platform using baculovirus (BacMam) to transiently express K2P channels in mammalian cells and a thallium flux assay to determine channel activity was developed, allowing the simultaneous screening of multiple targets. Importantly, this system, by allowing precise titration of channel function, allows optimization to facilitate the identification of activators. A representative set of channels (THIK-1, TWIK-1, TREK-2, TASK-3, and TASK-2) were screened against a library of Food and Drug Administration (FDA)-approved compounds and the LifeArc Index Set. Activators were then analyzed in concentration–response format across all channels to assess selectivity. Using the target class approach to investigate the K2P channels has enabled us to determine which of the K2Ps are amenable to small-molecule activation, de-risk multiple channels from a technical point of view, and identify a diverse range of previously undescribed pharmacology.

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