scholarly journals The Insensitivity of TASK-3 K2P Channels to External Tetraethylammonium (TEA) Partially Depends on the Cap Structure

2018 ◽  
Vol 19 (8) ◽  
pp. 2437 ◽  
Author(s):  
Guierdy Concha ◽  
Daniel Bustos ◽  
Rafael Zúñiga ◽  
Marcelo Catalán ◽  
Leandro Zúñiga
Keyword(s):  
Functional Role ◽  
Simulation Analysis ◽  
K Channel ◽  
Channel Blockers ◽  
Tyrosine Residue ◽  
K Channels ◽  
Enhanced Sensitivity ◽  
K2p Channels ◽  
Pore Domain

Two-pore domain K+ channels (K2P) display a characteristic extracellular cap structure formed by two M1-P1 linkers, the functional role of which is poorly understood. It has been proposed that the presence of the cap explains the insensitivity of K2P channels to several K+ channel blockers including tetraethylammonium (TEA). We have explored this hypothesis using mutagenesis and functional analysis, followed by molecular simulations. Our results show that the deletion of the cap structure of TASK-3 (TWIK-related acid-sensitive K+ channel) generates a TEA-sensitive channel with an IC50 of 11.8 ± 0.4 mM. The enhanced sensitivity to TEA displayed by the cap-less channel is also explained by the presence of an extra tyrosine residue at position 99. These results were corroborated by molecular simulation analysis, which shows an increased stability in the binding of TEA to the cap-less channel when a ring of four tyrosine is present at the external entrance of the permeation pathway. Consistently, Y99A or Y205A single-residue mutants generated in a cap-less channel backbone resulted in TASK-3 channels with low affinity to external TEA.

scholarly journals Atrial-selective K+ channel blockers: potential antiarrhythmic drugs in atrial fibrillation?

2017 ◽  
Vol 95 (11) ◽  
pp. 1313-1318 ◽  
Author(s):  
Ursula Ravens
Keyword(s):  
Atrial Fibrillation ◽  
Drug Targets ◽  
Antiarrhythmic Drugs ◽  
Drug Effects ◽  
K Channel ◽  
Channel Blockers ◽  
Electrophysiological Properties ◽  
Cardiac Functions ◽  
K2p Channels ◽  
Pore Domain

In the wake of demographic change in Western countries, atrial fibrillation has reached an epidemiological scale, yet current strategies for drug treatment of the arrhythmia lack sufficient efficacy and safety. In search of novel medications, atrial-selective drugs that specifically target atrial over other cardiac functions have been developed. Here, I will address drugs acting on potassium (K+) channels that are either predominantly expressed in atria or possess electrophysiological properties distinct in atria from ventricles. These channels include the ultra-rapidly activating, delayed outward-rectifying Kv1.5 channel conducting IKur, the acetylcholine-activated inward-rectifying Kir3.1/Kir3.4 channel conducting IK,ACh, the Ca2+-activated K+ channels of small conductance (SK) conducting ISK, and the two-pore domain K+ (K2P) channels (tandem of P domains, weak inward-rectifying K+ channels (TWIK-1), TWIK-related acid-sensitive K+ channels (TASK-1 and TASK-3)) that are responsible for voltage-independent background currents ITWIK-1, ITASK-1, and ITASK-3. Direct drug effects on these channels are described and their putative value in treatment of atrial fibrillation is discussed. Although many potential drug targets have emerged in the process of unravelling details of the pathophysiological mechanisms responsible for atrial fibrillation, we do not know whether novel antiarrhythmic drugs will be more successful when modulating many targets or a single specific one. The answer to this riddle can only be solved in a clinical context.

Enhanced role of K+ channels in relaxations of hypercholesterolemic rabbit carotid artery to NO

1995 ◽  
Vol 269 (3) ◽  
pp. H805-H811 ◽  
Author(s):  
S. Najibi ◽  
R. A. Cohen
Keyword(s):  
Carotid Artery ◽  
Sodium Nitroprusside ◽  
Channel Blocker ◽  
Isometric Tension ◽  
K Channel ◽  
K Channels ◽  
Rabbit Carotid Artery ◽  
Cyclic Monophosphate ◽  
Endothelium Dependent Relaxation

Endothelium-dependent relaxations to acetylcholine remain normal in the carotid artery of hypercholesterolemic rabbits, but unlike endothelium-dependent relaxations of normal rabbits, they are inhibited by charybdotoxin, a specific blocker of Ca(2+)-dependent K+ channels. Because nitric oxide (NO) is the mediator of endothelium-dependent relaxation and can activate Ca(2+)-dependent K+ channels directly or via guanosine 3',5'-cyclic monophosphate, the present study investigated the role of Ca(2+)-dependent K+ channels in relaxations caused by NO, sodium nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Brc-GMP) in hypercholesterolemic rabbit carotid artery. Isometric tension was measured in rabbit carotid artery denuded of endothelium from normal and hypercholesterolemic rabbits which were fed 0.5% cholesterol for 12 wk. Under control conditions, relaxations to all agents were similar in normal and hypercholesterolemic rabbit arteries. Charybdotoxin had no significant effect on relaxations of normal arteries to NO, sodium nitroprusside, or 8-BrcGMP, but the Ca(2+)-dependent K+ channel blocker significantly inhibited the relaxations caused by each of these agents in the arteries from hypercholesterolemic rabbits. By contrast, relaxations to the calcium channel blocker nifedipine were potentiated to a similar extent by charybdotoxin in both groups. In addition, arteries from hypercholesterolemic rabbits relaxed less than normal to sodium nitroprusside when contracted with depolarizing potassium solution. These results indicate that although nitrovasodilator relaxations are normal in the hypercholesterolemic rabbit carotid artery, they are mediated differently, and to a greater extent, by Ca(2+)-dependent K+ channels. These data also suggest that K+ channel-independent mechanism(s) are impaired in hypercholesterolemia.

Effect of Na+ and K+ channel blockade on baseline and anoxia-induced catecholamine release from rat carotid body

1994 ◽  
Vol 77 (6) ◽  
pp. 2606-2611 ◽  
Author(s):  
T. P. Doyle ◽  
D. F. Donnelly
Keyword(s):  
Carotid Body ◽  
K Channel ◽  
Channel Blockers ◽  
Nerve Activity ◽  
Sham Treatment ◽  
K Channels ◽  
Nerve Response ◽  
Carotid Bodies ◽  
Carotid Body Glomus Cells

Ionic membrane currents are hypothesized to play a major role in determining secretion from carotid body glomus cells, and increased secretion likely mediates the increase in nerve activity in response to hypoxia. The hypothesis that Na+ and K+ channels play an important role in determining secretion and nerve activity was tested by measuring single-fiber afferent nerve activity along with an estimate of free tissue catecholamine using Nafion-covered carbon-fiber micro-electrodes placed in rat carotid bodies in vitro. Baseline and anoxia-stimulated (1 min duration; PO2 of approximately 0 Torr at nadir) levels were quantified. Sham treatment had no significant effect. Tetrodotoxin (2 microns) ablated the nerve activity and reduced peak catecholamine (19.5 +/- 3.1 to 14.5 +/- 3.4 microM; P < 0.05). Cesium (10 microns) had no effect on catecholamine but reduced the nerve response (19.8 +/- 2.7 to 7.8 +/- 2.0 Hz; P < 0.05). 4-Aminopyridine (4 mM) significantly reduced the nerve response (17.2 +/- 3.7 to 4.9 +/- 1.9 Hz; P < 0.05) and increased the baseline (0.9 +/- 0.2 to 3.1 +/- 0.8 microM; P < 0.05) and reduced the peak catecholamine (10.0 to 4.3 +/- 0.8 microM; P < 0.05) levels. These results demonstrate that Na+ and K+ channels play an important role in modulating the secretory and nerve responses. However, channel blockers do not emulate severe hypoxia, suggesting that hypoxia transduction procedes, at least in part, through an alternate pathway.

Rat Prl and TSH secretion are regulated differently by K(+)-channel blockers

1994 ◽  
Vol 266 (1) ◽  
pp. E39-E43 ◽  
Author(s):  
X. Wang ◽  
T. Inukai ◽  
M. A. Greer ◽  
S. E. Greer
Keyword(s):  
Channel Blocker ◽  
Cell Types ◽  
Inhibitory Effect ◽  
Thyroid Stimulating Hormone ◽  
K Channel ◽  
Channel Blockers ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
K Channels ◽  
Tsh Secretion

All four different K(+)-channel blockers [tetraethylammonium (TEA), a nonselective K(+)-channel blocker; tolbutamide, an ATP-sensitive K(+)-channel blocker; quinine and 4-aminopyridine, both primarily voltage-dependent K(+)-channel blockers] stimulated prolactin (Prl) secretion by acutely dispersed anterior pituitary cells but had no effect on thyroid-stimulating hormone (TSH) secretion. TEA stimulated Prl secretion in a dose-dependent manner between 1 microM and 20 mM, but even as high as 20 mM, TEA did not induce TSH secretion. Valinomycin (2 microM), a K+ ionophore, inhibited both basal and TEA-induced Prl secretion. TEA-stimulated Prl secretion was abolished by using a Ca(2+)-depleted medium or adding 10 microM dopamine. TEA did not reverse the inhibitory effect of dopamine on thyrotropin-releasing hormone-induced Prl secretion. Our data indicate that K+ channels may play a role in the secretion of adenohypophysial hormones that is idiosyncratic for each hormone. Differences in the role of K+ channels may reflect differences between the various pituitary cell types in plasma membrane ion channel composition, membrane potential, or the mechanism of exocytosis.

Heterogeneous populations of K+ channels mediate EDRF release to flow but not agonists in rabbit aorta

1994 ◽  
Vol 266 (2) ◽  
pp. H590-H596 ◽  
Author(s):  
I. R. Hutcheson ◽  
T. M. Griffith
Keyword(s):  
Shear Stress ◽  
Rabbit Aorta ◽  
Katp Channels ◽  
K Channel ◽  
K Channels ◽  
Kca Channels ◽  
Endothelium Derived Relaxing Factor ◽  
Endothelium Dependent Relaxation ◽  
High Conductance

We have investigated the role of Ca(2+)- and ATP-sensitive K+ channels (KCa and KATP, respectively) in flow- and agonist-stimulated release of endothelium-derived relaxing factor (EDRF). Segments of rabbit abdominal aorta, perfused at constant flow with buffer containing indomethacin, were used as a source of EDRF in cascade bioassay, and responses to endothelium-dependent agonists were studied isometrically in rings of the same tissue in the absence of flow. Apamin, charybdotoxin (ChTX), and tetraethylammonium (TEA) were used to block a variety of low, medium, and high conductance KCa channels, and glibenclamide was used to block KATP channels. The effects of flow pulsatility were studied at pulse frequencies ranging from 0.15 to 9.75 Hz, and time-averaged shear stress was manipulated by adding dextran (80,000 mol wt) to the perfusate to increase its viscosity. Frequency-related EDRF release was maximal at approximately 5 Hz and attenuated by apamin, TEA, and ChTX, but not by glibenclamide. EDRF release stimulated by increased viscosity was attenuated by TEA, ChTX, and glibenclamide, but not by apamin. In marked contrast, EDRF release stimulated by acetylcholine and ATP was unaffected by blockade of either KCa or KATP channels. We conclude that a spectrum of KCa channel subtypes mediates endothelial transduction of the oscillatory component of pulsatile flow and that KATP channels may be additionally involved in the transduction of time-averaged shear stress. In contrast, agonist-stimulated endothelium-dependent relaxation is independent of K+ channel activation in rabbit aorta.

scholarly journals Voltage-sensitive potassium channels in Limulus ventral photoreceptors.

1978 ◽  
Vol 71 (1) ◽  
pp. 101-120 ◽  
Author(s):  
J S Pepose ◽  
J E Lisman
Keyword(s):  
Functional Role ◽  
Resting Potential ◽  
Reverse Direction ◽  
Voltage Range ◽  
K Channels ◽  
Response Intensity ◽  
Intracellular Injection ◽  
Voltage Dependent ◽  
Ionic Basis

The steady-state slope conductance of Limulus ventral photoreceptors increases markedly when the membrane is depolarized from rest. The ionic basis of this rectification has been examined with a voltage-clamp technique. Tail currents that occur when membrane potential is repolarized after having been depolarized have been identified. The tail currents reverse direction at a voltage that becomes more positive when Ko is increased. Rectification is reduced by extracellular 4-aminopyridine and by intracellular injection of tetra-ethyl-ammonium (TEA). These results indicate that the membrane rectification around resting potential is due primarily to voltage-sensitive K+ channels. The increase in gK caused by depolarization is not mediated by a voltage-dependent rise in in Cai++, since intracellular injection of Ca++ causes a decrease rather than an increase in slope conductance. TEA can be used to examine the functional role of the K+ channels because it blocks them without substantially affecting the light-activated Na+ conductance. The effect of TEA on response-intensity curves shows that the K+ channels serve to compress the voltage range of receptor potentials.

scholarly journals A Conserved Arginine Residue in the Pore Region of an Inward Rectifier K Channel (IRK1) as an External Barrier for Cationic Blockers

1997 ◽  
Vol 110 (6) ◽  
pp. 665-677 ◽  
Author(s):  
Ravshan Z. Sabirov ◽  
Tomoko Tominaga ◽  
Akiko Miwa ◽  
Yasunobu Okada ◽  
Shigetoshi Oiki
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
K Channel ◽  
Channel Blockers ◽  
Channel Activity ◽  
Wild Type ◽  
K Channels ◽  
Blocking Rate ◽  
External Barrier ◽  
Kir2.1 Channel

The number, sign, and distribution of charged residues in the pore-forming H5 domain for inward-rectifying K channels (IRK1) are different from the otherwise homologous H5 domains of other voltage-gated K channels. We have mutated Arg148, which is perfectly conserved in all inward rectifiers, to His in the H5 of IRK1 (Kir2.1). Channel activity was lost by the mutation, but coexpression of the mutant (R148H) along with the wild-type (WT) mRNA revealed populations of channels with reduced single-channel conductances. Long-lasting and flickery sublevels were detected exclusively for the coexpressed channels. These findings indicated that the mutant subunit formed hetero-oligomers with the WT subunit. The permeability ratio was altered by the mutation, while the selectivity sequence (K+ &gt; Rb+ &gt; NH4+ &gt;&gt; Na+) was preserved. The coexpression made the IRK1 channel more sensitive to extracellular block by Mg2+ and Ca2+, and turned this blockade from a voltage-independent to a -dependent process. The sensitivity of the mutant channels to Mg2+ was enhanced at higher pH and by an increased ratio of mutant:WT mRNA, suggesting that the charge on the Arg site controlled the sensitivity. The blocking rate of open channel blockers, such as Cs+ and Ba2+, was facilitated by coexpression without significant change in the steady state block. Evaluation of the electrical distance to the binding site for Mg2+ or Ca2+ and that to the barrier peak for block by Cs+ or Ba2+ suggest that Arg148 is located between the external blocking site for Mg2+ or Ca2+ and the deeper blocking site for Cs+ or Ba2+ in the IRK1 channel. It is concluded that Arg148 serves as a barrier to cationic blockers, keeping Mg2+ and Ca2+ out from the electric field of the membrane.

Transformation of renal tubule epithelial cells by simian virus-40 is associated with emergence of Ca2+-insensitive K+ channels and altered mitogenic sensitivity to K+ channel blockers

1992 ◽  
Vol 151 (1) ◽  
pp. 113-125 ◽  
Author(s):  
Jacques Teulon ◽  
Pierre M. Ronco ◽  
Monique Geniteau-Legendre ◽  
B�atrice Baudouin ◽  
Simone Estrade ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Renal Tubule ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
K Channel ◽  
Channel Blockers ◽  
K Channels
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