Functional effects of 20-HETE on human bronchi: hyperpolarization and relaxation due to BKCa channel activation

2007 ◽  
Vol 293 (4) ◽  
pp. L1037-L1044 ◽  
Author(s):  
Caroline Morin ◽  
Marco Sirois ◽  
Vincent Echave ◽  
Marcio M. Gomes ◽  
Eric Rousseau
Keyword(s):  
Isometric Tension ◽  
Bkca Channel ◽  
Channel Activation ◽  
Relaxant Effect ◽  
Electrophysiological Effect ◽  
Resting Tone ◽  
Enzymatic Pathways ◽  
Microelectrode Measurements ◽  
Cytochrome P 450 ◽  
Human Bronchi

Airway smooth muscle (ASM) metabolizes arachidonic acid (AA) through various enzymatic pathways, including cytochrome P-450 (CYP-450) ω-hydroxylase, which leads to the production of 20-hydroxyeicosatetraenoic acid (20-HETE). The goal of this study was to delineate the mode of action of 20-HETE in human ASM cells. Isometric tension measurements demonstrated that 20-HETE induced a concentration-dependent relaxant effect in ASM on bronchi precontracted with either methacholine or AA. Relaxing effects of 20-HETE on resting tone were prevented by 10 nM iberiotoxin (IbTx), a BKCa channel inhibitor. Microelectrode measurements showed that exogenous additions of 20-HETE (0.1–10 μM) hyperpolarized the membrane potential of human ASM cells. This concentration-dependent electrophysiological effect induced by the eicosanoid was prevented by 10 nM IbTx. Complementary experiments, using the planar lipid bilayer reconstitution technique, demonstrated that 20-HETE activated reconstituted BKCa channels at low free Ca2+ concentrations. Together, these results indicate that 20-HETE-dependent activation of BKCa channels is responsible for the hyperpolarization and controlled relaxation of ASM in human distal bronchi.

Relaxing effects of 5-oxo-ETE on human bronchi involve BKCa channel activation

2007 ◽  
Vol 83 (4) ◽  
pp. 311-319 ◽  
Author(s):  
Caroline Morin ◽  
Marco Sirois ◽  
Vincent Échave ◽  
Marcio M. Gomes ◽  
Eric Rousseau
Keyword(s):  
Bkca Channel ◽  
Channel Activation ◽  
Human Bronchi

Inhibitory Effects of Etomidate and Ketamine on Adenosine Triphosphate–Sensitive Potassium Channel Relaxation in Canine Pulmonary Artery

2003 ◽  
Vol 98 (1) ◽  
pp. 104-113 ◽  
Author(s):  
Ju-Tae Sohn ◽  
Paul A. Murray
Keyword(s):  
Adenosine Triphosphate ◽  
Inhibitory Effect ◽  
Isometric Tension ◽  
Relaxation Response ◽  
Inhibitory Effects ◽  
Channel Activation ◽  
K Channels ◽  
Dependent Component ◽  
Pulmonary Arterial ◽  
Relaxation Responses

Background The authors recently demonstrated that etomidate and ketamine attenuated endothelium-dependent pulmonary vasorelaxation mediated by nitric oxide and Ca -activated K + channels. In the current study, they tested the hypothesis that these intravenous anesthetics inhibit pulmonary vasorelaxation mediated by adenosine triphosphate-sensitive potassium (K + ATP ) channel activation. Methods Endothelium intact and denuded pulmonary arterial rings were suspended in organ chambers for isometric tension recording. The effects of etomidate (5 x 10(-6) and 5 x 10(-5) m) and ketamine (5 x 10(-5) and 10(-4) m) on vasorelaxation responses to lemakalim (K + ATP channel activator), prostacyclin, and papaverine were assessed in phenylephrine-precontracted rings. The effect of cyclooxygenase inhibition with indomethacin was assessed in some protocols. Results Etomidate (5 x 10(-6) m) only inhibited the vasorelaxant response to lemakalim in endothelium intact rings, whereas a higher concentration of etomidate (5 x 10(-5) m) inhibited relaxation in both intact and endothelium-denuded rings. Pretreatment with indomethacin abolished the endothelium-dependent attenuation of lemakalim-induced relaxation caused by etomidate. Ketamine (5 x 10(-5) and 10(-5) m) inhibited the relaxation response to lemakalim to the same extent in both endothelium-intact and -denuded rings, and this effect was not prevented by indomethacin pretreatment. Etomidate and ketamine had no effect on the relaxation responses to prostacyclin or papaverine. Conclusions These results indicate that etomidate, but not ketamine, attenuates the endothelium-dependent component of lemakalim-induced pulmonary vasorelaxation an inhibitory effect on the cyclooxygenase pathway. Both anesthetics inhibit K + ATP -mediated pulmonary vasorelaxation a direct effect on pulmonary vascular smooth muscle.

The relaxant effect of nifedipine in human uterine smooth muscle and the BKCa channel

2008 ◽  
Vol 198 (2) ◽  
pp. 237.e1-237.e8 ◽  
Author(s):  
Audrey T. Moynihan ◽  
Terry J. Smith ◽  
John J. Morrison
Keyword(s):  
Smooth Muscle ◽  
Bkca Channel ◽  
Relaxant Effect ◽  
Uterine Smooth Muscle

EETs relax airway smooth muscle via an EpDHF effect: BKCa channel activation and hyperpolarization

2001 ◽  
Vol 280 (5) ◽  
pp. L965-L973 ◽  
Author(s):  
Catherine Benoit ◽  
Barbara Renaudon ◽  
Dany Salvail ◽  
Eric Rousseau
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Molecular Mechanisms ◽  
Muscle Tone ◽  
Muscle Relaxation ◽  
Smooth Muscle Relaxation ◽  
Epoxyeicosatrienoic Acids ◽  
Bkca Channel ◽  
Channel Activity ◽  
Cytochrome P 450

Epoxyeicosatrienoic acids (EETs) are produced from arachidonic acid via the cytochrome P-450 epoxygenase pathway. EETs are able to modulate smooth muscle tone by increasing K+ conductance, hence generating hyperpolarization of the tissues. However, the molecular mechanisms by which EETs induce smooth muscle relaxation are not fully understood. In the present study, the effects of EETs on airway smooth muscle (ASM) were investigated using three electrophysiological techniques. 8,9-EET and 14,15-EET induced concentration-dependent relaxations of the ASM precontracted with a muscarinc agonist (carbamylcholine chloride), and these relaxations were partly inhibited by 10 nM iberiotoxin (IbTX), a specific large-conductance Ca2+-activated K+ (BKCa) channel blocker. Moreover, 3 μM 8,9- or 14,15-EET induced hyperpolarizations of −12 ± 3.5 and −16 ± 3 mV, with EC50 values of 0.13 and 0.14 μM, respectively, which were either reversed or blocked on addition of 10 nM IbTX. These results indicate that BKCa channels are involved in hyperpolarization and participate in the relaxation of ASM. In addition, complementary experiments demonstrated that 8,9- and 14,15-EET activate reconstituted BKCa channels at low free Ca2+ concentrations without affecting their unitary conductance. These increases in channel activity were IbTX sensitive and correlated well with the IbTX-sensitive hyperpolarization and relaxation of ASM. Together these results support the view that, in ASM, the EETs act through an epithelium-derived hyperpolarizing factorlike effect.

Afferent arteriolar response to arachidonic acid: involvement of metabolic pathways

1996 ◽  
Vol 271 (1) ◽  
pp. F87-F93 ◽  
Author(s):  
J. D. Imig ◽  
L. G. Navar
Keyword(s):  
Arachidonic Acid ◽  
Cyclooxygenase Inhibition ◽  
Lipoxygenase Inhibition ◽  
Vasoconstrictor Response ◽  
Afferent Arterioles ◽  
Renal Microvasculature ◽  
Differential Responses ◽  
Enzymatic Pathways ◽  
Cytochrome P 450

Arachidonic acid (AA) metabolites have been implicated in the control of renal hemodynamics, but the nature of the metabolites produced by renal cells when AA is released has remained uncertain. Experiments were performed using the in vitro perfused juxtamedullary nephron preparation to examine the effects of perfusion and superfusion of AA on the renal microvasculature. Extraluminal exposure of the vessels by superfusion with solutions containing 0.1, 1.0, and 10 microM AA decreased afferent arteriolar diameter by 8 +/- 2, 16 +/- 3, and 20 +/- 3%, respectively. The same doses of AA added to the perfusate produced a similar afferent arteriolar vasoconstriction. Inhibition of the major enzymatic pathways unmasked differential responses of AA that were dependent on the direction from which the vasculature was exposed to AA. 17-Octadecynoic acid (1 microM), an inhibitor of the cytochrome P-450 pathway, eliminated the vasoconstrictor response to superfused AA but had little effect on the response to perfused AA. Lipoxygenase inhibition with baicalein (0.5 microM) did not alter the afferent arteriolar vasoconstriction during superfusion with AA but did attenuate the vasoconstrictor response to perfused AA by 34%. Cyclooxygenase inhibition with 10 microM indomethacin reduced the afferent arteriolar response to superfusion with 10 microM AA by 46%, but the responses to perfusion with AA were reversed, leading to the unmasking of a 17% afferent arteriolar dilation. The AA-induced vasorelaxation observed during cyclooxygenase inhibition was prevented by the subsequent addition of a P-450 inhibitor. Additionally, after endothelial removal with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), the vasodilatory response reverted to a vasoconstriction. The results of this study demonstrate that in the rat, AA metabolites exert predominant actions on afferent arterioles, but differential responses are mediated via different enzymatic pathways depending on the origin of AA. Increased AA availability of intraluminal origin leads to production of cyclooxygenase-derived vasoconstrictor metabolites and also to endothelial-derived cytochrome P-450 vasodilatory metabolites. In contrast, increased AA availability of interstitial origin leads to production of vasoconstrictor cytochrome P-450 metabolites.

BKCa channel activation by membrane-associated cGMP kinase may contribute to uterine quiescence in pregnancy

2000 ◽  
Vol 279 (6) ◽  
pp. C1751-C1759 ◽  
Author(s):  
Xiao-Bo Zhou ◽  
Ge-Xin Wang ◽  
Peter Ruth ◽  
Bernd Hüneke ◽  
Michael Korth
Keyword(s):  
Bkca Channel ◽  
Channel Activity ◽  
Inhibitory Peptide ◽  
Channel Activation ◽  
Myometrial Cells ◽  
Maximal Activation ◽  
Channel Expression ◽  
Membrane Bound ◽  
Calcium Activated Potassium Channel ◽  
Inside Out

We investigated the influence of pregnancy on large-conductance calcium-activated potassium channel (BKCa) activity ( NP o) and on channel expression in membranes of isolated human myometrial smooth muscle cells. NP o in inside-out patches was higher in pregnant myometria (PM) compared with nonpregnant myometria (NPM), and the half-maximal activation potential was shifted by 39 mV to more negative potentials. This effect was not due to an enhanced BKCachannel expression. In the presence of cAMP kinase (PKA) or cGMP kinase (PKG), NP o increased in patches from PM but decreased in those from NPM. Western blot analysis and use of a specific PKG inhibitor (1 μM KT-5823) verified the existence of a partially active membrane-associated PKG. Inhibition of PKA by 100 nM PKI, the inhibitory peptide of PKA, had no effect on NP o. 8- p-Chlorophenylthio-cGMP (8-pCPT-cGMP) hyperpolarized cells from PM. This effect was abolished by iberiotoxin, a specific blocker of BKCachannels. It is concluded that an endogenous, membrane-bound PKG in myometrial cells specifically enhances BKCa channel activity during pregnancy and thus may contribute to uterine quiescence during pregnancy.

scholarly journals The β1 Subunit Enhances Oxidative Regulation of Large-Conductance Calcium-activated K+ Channels

2004 ◽  
Vol 124 (4) ◽  
pp. 357-370 ◽  
Author(s):  
Lindsey Ciali Santarelli ◽  
Jianguo Chen ◽  
Stefan H. Heinemann ◽  
Toshinori Hoshi
Keyword(s):  
Bkca Channel ◽  
Open Probability ◽  
Bkca Channels ◽  
Additional Increase ◽  
Channel Activation ◽  
Α Subunit ◽  
Voltage Range ◽  
Virtual Absence ◽  
Methionine Residues ◽  
Oxidative Regulation

Oxidative stress may alter the functions of many proteins including the Slo1 large conductance calcium-activated potassium channel (BKCa). Previous results demonstrated that in the virtual absence of Ca2+, the oxidant chloramine-T (Ch-T), without the involvement of cysteine oxidation, increases the open probability and slows the deactivation of BKCa channels formed by human Slo1 (hSlo1) α subunits alone. Because native BKCa channel complexes may include the auxiliary subunit β1, we investigated whether β1 influences the oxidative regulation of hSlo1. Oxidation by Ch-T with β1 present shifted the half-activation voltage much further in the hyperpolarizing direction (−75 mV) as compared with that with α alone (−30 mV). This shift was eliminated in the presence of high [Ca2+]i, but the increase in open probability in the virtual absence of Ca2+ remained significant at physiologically relevant voltages. Furthermore, the slowing of channel deactivation after oxidation was even more dramatic in the presence of β1. Oxidation of cysteine and methionine residues within β1 was not involved in these potentiated effects because expression of mutant β1 subunits lacking cysteine or methionine residues produced results similar to those with wild-type β1. Unlike the results with α alone, oxidation by Ch-T caused a significant acceleration of channel activation only when β1 was present. The β1 M177 mutation disrupted normal channel activation and prevented the Ch-T–induced acceleration of activation. Overall, the functional effects of oxidation of the hSlo1 pore-forming α subunit are greatly amplified by the presence of β1, which leads to the additional increase in channel open probability and the slowing of deactivation. Furthermore, M177 within β1 is a critical structural determinant of channel activation and oxidative sensitivity. Together, the oxidized BKCa channel complex with β1 has a considerable chance of being open within the physiological voltage range even at low [Ca2+]i.

Rivaroxaban-Mediated Vascular Relaxation As a Potential Cause of Headaches and Dizziness

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 2334-2334
Author(s):  
Jon Mabley ◽  
Greg Scutt ◽  
Kathryn Jane Lang ◽  
Jignesh P Patel ◽  
Roopen Arya
Keyword(s):  
Thoracic Aorta ◽  
Research Funding ◽  
Adult Population ◽  
Underlying Mechanism ◽  
Physiological Effect ◽  
Isometric Tension ◽  
Common Side Effect ◽  
Sprague Dawley ◽  
Relaxant Effect ◽  
Rat Thoracic Aorta

Abstract The availability of the direct Xa inhibitors apixaban, edoxaban and rivaroxaban in clinical practice is leading a paradigm shift in anticoagulation for the management of venous thromboembolism (VTE) and stroke prophylaxis in the context of non-valvular atrial fibrillation (AF). A common side effect experienced by patients receiving rivaroxaban in clinical trials was dizziness and headache, with a reported incidence of between 1 in 10 and 1 in 100 patients. Clinical experience has seen patients reporting rivaroxaban associated headaches and dizziness, leading to discontinuation of therapy. Given that widespread use of these agents is likely to be within an older adult population, it is important to understand the mechanism behind clinical observations which may then allow us to determine why some patients are affected more than others. We hypothesise that rivaroxaban directly causes vascular arteriodilation, resulting in headaches and dizziness requiring discontinuation of treatment. To test this hypothesis the effects of rivaroxaban on phenylephrine pre-contracted rat aortic rings was investigated. Thoracic aorta from male Sprague-Dawley rats (180-220g) were dissected and cut into rings of 2-3mm prior to being mounted under a preload tension of 1.5g in Krebs filled organ baths. Isometric tension of the rings was measured with isometric transducers (Danish Myo Technology, Aarhus, Denmark) digitised using a Power lab system. Following a phenylephrine dose-response curve the aortic rings were pre-contracted with 1 µM phenylephrine before measuring the relaxant effect of rivaroxaban (0.001-0.3 µM) or a similar volume of the vehicle dimethyl sulfoxide (DMSO). Statistical analysis was carried out using two-way ANOVA with Bonferroni's correction, where p<0.05 was considered significant. Exposure of aortic rings to both rivaroxaban and the vehicle DMSO caused relaxation. However, the relaxation observed with rivaroxaban was significantly greater than that observed with the vehicle (Fig 1). Our preliminary data suggests that rivaroxaban may have a direct arteriodilatory effect. This arteriodilatory effect of rivaroxaban may provide a possible explanation for dizziness and headaches experienced by some rivaroxaban treated patients. Further work is required to determine the underlying mechanism of rivaroxaban-mediated vaso-relaxant effect as well as determining if the other Xa inhibitors apixaban and edoxaban also share this physiological effect, and if so, to what extent. Figure 1. Exposure of rat thoracic aorta rings to rivaroxaban and the vehicle DMSO caused relaxation. Rivaroxaban produced significantly more relaxation as compared to DMSO alone (p<0.05). Data is expressed as mean ± SEM from 12 animals; †p<0.05 vs. DMSO alone Figure 1. Exposure of rat thoracic aorta rings to rivaroxaban and the vehicle DMSO caused relaxation. Rivaroxaban produced significantly more relaxation as compared to DMSO alone (p<0.05). Data is expressed as mean ± SEM from 12 animals; †p<0.05 vs. DMSO alone Disclosures Patel: Bayer plc: Research Funding. Arya:Bayer plc: Research Funding.

scholarly journals BKCa channel activation increases cardiac contractile recovery following hypothermic ischemia/reperfusion

2015 ◽  
Vol 309 (4) ◽  
pp. H625-H633 ◽  
Author(s):  
Brenda Cordeiro ◽  
Dmitry Terentyev ◽  
Richard T. Clements
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Mitochondrial Membrane ◽  
Left Ventricular ◽  
Bkca Channel ◽  
Ros Generation ◽  
H9c2 Cells ◽  
Bkca Channels ◽  
Channel Activation

Mitochondrial Ca2+-activated large-conductance K+ (BKCa) channels are thought to provide protection during ischemic insults in the heart. Rottlerin (mallotoxin) has been implicated as a potent BKCa activator. The purpose of this study was twofold: 1) to investigate the efficacy of BKCa channel activation as a cardioprotective strategy during ischemic cardioplegic arrest and reperfusion (CP/R) and 2) to assess the specificity of rottlerin for BKCa channels. Wild-type (WT) and BKCa knockout (KO) mice were subjected to an isolated heart model of ischemic CP/R. A mechanism of rottlerin-induced cardioprotection was also investigated using H9c2 cells subjected to in vitro CP/reoxygenation and assessed for mitochondrial membrane potential and reactive oxygen species (ROS) production. CP/R decreased left ventricular developed pressure, positive and negative first derivatives of left ventricular pressure, and coronary flow (CF) in WT mice. Rottlerin dose dependently increased the recovery of left ventricular function and CF to near baseline levels. BKCa KO hearts treated with or without 500 nM rottlerin were similar to WT CP hearts. H9c2 cells subjected to in vitro CP/R displayed reduced mitochondrial membrane potential and increased ROS generation, both of which were significantly normalized by rottlerin. We conclude that activation of BKCa channels rescues ischemic damage associated with CP/R, likely via effects on improved mitochondrial membrane potential and reduced ROS generation.

scholarly journals Type 1 IP3 receptors activate BKCa channels via local molecular coupling in arterial smooth muscle cells

2010 ◽  
Vol 136 (3) ◽  
pp. 283-291 ◽  
Author(s):  
Guiling Zhao ◽  
Zachary P. Neeb ◽  
M. Dennis Leo ◽  
Judith Pachuau ◽  
Adebowale Adebiyi ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Bkca Channel ◽  
Ip3 Receptors ◽  
Arterial Smooth Muscle ◽  
Bkca Channels ◽  
Channel Activation ◽  
Arterial Smooth Muscle Cells

Plasma membrane large-conductance Ca2+-activated K+ (BKCa) channels and sarcoplasmic reticulum inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) are expressed in a wide variety of cell types, including arterial smooth muscle cells. Here, we studied BKCa channel regulation by IP3 and IP3Rs in rat and mouse cerebral artery smooth muscle cells. IP3 activated BKCa channels both in intact cells and in excised inside-out membrane patches. IP3 caused concentration-dependent BKCa channel activation with an apparent dissociation constant (Kd) of ∼4 µM at physiological voltage (−40 mV) and intracellular Ca2+ concentration ([Ca2+]i; 10 µM). IP3 also caused a leftward-shift in BKCa channel apparent Ca2+ sensitivity and reduced the Kd for free [Ca2+]i from ∼20 to 12 µM, but did not alter the slope or maximal Po. BAPTA, a fast Ca2+ buffer, or an elevation in extracellular Ca2+ concentration did not alter IP3-induced BKCa channel activation. Heparin, an IP3R inhibitor, and a monoclonal type 1 IP3R (IP3R1) antibody blocked IP3-induced BKCa channel activation. Adenophostin A, an IP3R agonist, also activated BKCa channels. IP3 activated BKCa channels in inside-out patches from wild-type (IP3R1+/+) mouse arterial smooth muscle cells, but had no effect on BKCa channels of IP3R1-deficient (IP3R1−/−) mice. Immunofluorescence resonance energy transfer microscopy indicated that IP3R1 is located in close spatial proximity to BKCa α subunits. The IP3R1 monoclonal antibody coimmunoprecipitated IP3R1 and BKCa channel α and β1 subunits from cerebral arteries. In summary, data indicate that IP3R1 activation elevates BKCa channel apparent Ca2+ sensitivity through local molecular coupling in arterial smooth muscle cells.

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