scholarly journals Neuroleptics antagonize a calcium-activated potassium channel in airway smooth muscle.

1987 ◽  
Vol 89 (2) ◽  
pp. 339-352 ◽  
Author(s):  
J D McCann ◽  
M J Welsh
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Dissociation Constants ◽  
Rank Order ◽  
K Channel ◽  
Airway Smooth Muscle Cells ◽  
Open Probability ◽  
K Channels ◽  
Channel Inhibition ◽  
Equilibrium Dissociation Constants

We examined the effect of neuroleptics on Ca-activated K channels from dog airway smooth muscle cells. Because these agents inhibit a variety of other Ca-mediated processes, it seemed possible that they might also inhibit Ca-activated K channels. In excised, inside-out patches, several neuroleptics potently and reversibly inhibited the K channel from the internal but not the external surface of the patch. Measurements of the effect on open probability and open- and closed-state durations support a simple kinetic model in which neuroleptics bind to and block the open channel. Inhibition by neuroleptics was moderately voltage dependent, with blockers less potent at hyperpolarizing voltages. The relationship between voltage and the dissociation constant for the blocker suggests that the binding site is one-third of the way across the channel's electrical field. Equilibrium dissociation constants for the drug-channel complex were: haloperidol, 1.0 +/- 0.1 microM; trifluoperazine, 1.4 +/- 0.1 microM; thioridazine, 2.4 +/- 0.1 microM; and chlorpromazine, 2.0 microM. This rank-order potency is different from their potency as calmodulin inhibitors, which suggests that neuroleptics bind to the channel rather than a calmodulin-channel complex.

Large conducting potassium channel reconstituted from airway smooth muscle

1992 ◽  
Vol 262 (3) ◽  
pp. L327-L336 ◽  
Author(s):  
D. Savaria ◽  
C. Lanoue ◽  
A. Cadieux ◽  
E. Rousseau
Keyword(s):  
Smooth Muscle ◽  
Lipid Bilayers ◽  
Airway Smooth Muscle ◽  
Single Channel ◽  
Specific Inhibitor ◽  
Physiological Role ◽  
Membrane Receptors ◽  
K Channel ◽  
Open Probability ◽  
K Channels

Microsomal fractions were prepared from canine and bovine airway smooth muscle (ASM) by differential and gradient centrifugations. Surface membrane vesicles were characterized by binding assays and incorporated into planar lipid bilayers. Single-channel activities were recorded in symmetric or asymmetric K+ buffer systems and studied under voltage and Ca2+ clamp conditions. A large-conductance K(+)-selective channel (greater than 220 pS in 150 mM K+) displaying a high Ca2+, low Ba2+, and charybdotoxin (CTX) sensitivity was identified. Time analysis of single-channel recordings revealed a complex kinetic behavior compatible with the previous schemes proposed for Ca(2+)-activated K+ channels in a variety of biological surface membranes. We now report that the open probability of the channel at low Ca2+ concentration is enhanced on in vitro phosphorylation, which is mediated via an adenosine 3',5'-cyclic monophosphate-dependent protein kinase. In addition to this characterization at the molecular level, a second series of pharmacological experiments were designed to assess the putative role of this channel in ASM strips. Our results show that 50 nM CTX, a specific inhibitor of the large conducting Ca(2+)-dependent K+ channel, prevents norepinephrine transient relaxation on carbamylcholine-precontracted ASM strips. It was also shown that CTX reversed the steady-state relaxation induced by vasoactive intestinal peptide and partially antagonized further relaxation induced by cumulative doses of this potent bronchodilatator. Thus it is proposed that the Ca(2+)-activated K+ channels have a physiological role because they are indirectly activated on stimulation of various membrane receptors via intracellular mechanisms.

scholarly journals Estrogen receptors differentially regulate intracellular calcium handling in human nonasthmatic and asthmatic airway smooth muscle cells

2020 ◽  
Vol 318 (1) ◽  
pp. L112-L124 ◽  
Author(s):  
Sangeeta Bhallamudi ◽  
Jennifer Connell ◽  
Christina M Pabelick ◽  
Y. S. Prakash ◽  
Venkatachalem Sathish
Keyword(s):  
Smooth Muscle ◽  
Estrogen Receptors ◽  
Intracellular Calcium ◽  
Airway Smooth Muscle ◽  
Airway Remodeling ◽  
Clinical Findings ◽  
Calcium Handling ◽  
Airway Smooth Muscle Cells ◽  
Adult Women ◽  
Channel Inhibition

Asthma is defined as chronic inflammation of the airways and is characterized by airway remodeling, hyperresponsiveness, and acute bronchoconstriction of airway smooth muscle (ASM) cells. Clinical findings suggest a higher incidence and severity of asthma in adult women, indicating a concrete role of sex steroids in modulating the airway tone. Estrogen, a major female sex steroid mediates its role through estrogen receptors (ER) ERα and ERβ, which are shown to be expressed in human ASM, and their expression is upregulated in lung inflammation and asthma. Previous studies suggested rapid, nongenomic signaling of estrogen via ERs reduces intracellular calcium ([Ca2+]i), thereby promoting relaxation of ASM. However, long-term ER activation on [Ca2+]i regulation in human ASM during inflammation or in asthma is still not known. In Fura-2-loaded nonasthmatic and asthmatic human ASM cells, we found that prolonged (24 h) exposure to ERα agonist (PPT) increased [Ca2+]i response to histamine, whereas ERβ activation (WAY) led to decreased [Ca2+] compared with vehicle. This was further confirmed by ER overexpression and knockdown studies using various bronchoconstrictor agents. Interestingly, ERβ activation was more effective than 17β-estradiol in reducing [Ca2+]i responses in the presence of TNF-α or IL-13, while no observable changes were noticed with PPT in the presence of either cytokine. The [Ca2+]i-reducing effects of ERβ were mediated partially via L-type calcium channel inhibition and increased Ca2+ sequestration by sarcoplasmic reticulum. Overall, these data highlight the differential signaling of ERα and ERβ in ASM during inflammation. Specific ERβ activation reduces [Ca2+]i in the inflamed ASM cells and is likely to play a crucial role in regulating ASM contractility, thereby relaxing airways.

Potent inhibition of the aortic smooth muscle maxi-K channel by clinical doses of ethanol

2000 ◽  
Vol 279 (4) ◽  
pp. C1107-C1115 ◽  
Author(s):  
F. S. Walters ◽  
M. Covarrubias ◽  
J. S. Ellingson
Keyword(s):  
Smooth Muscle ◽  
Lipid Bilayers ◽  
Single Channel ◽  
K Channel ◽  
Open Probability ◽  
K Channels ◽  
Aortic Smooth Muscle ◽  
Slope Factor ◽  
The Mean ◽  
Relationship Change

We investigated the effects of clinically relevant ethanol concentrations (5–20 mM) on the single-channel kinetics of bovine aortic smooth muscle maxi-K channels reconstituted in lipid bilayers (1:1 palmitoyl-oleoyl-phosphatidylethanolamine: palmitoyl-oleoyl-phosphatidylcholine). Ethanol at 10 and 20 mM decreased the channel open probability ( P o) by 75 ± 20.3% mainly by increasing the mean closed time (+82 to +960%, n = 7). In some instances, ethanol also decreased the mean open time (−40.8 ± 22.5%). The P o-voltage relation in the presence of 20 mM ethanol exhibited a rightward shift in the midpoint of voltage activation (Δ V ½ ≅ 17 mV), a slightly steeper relationship (change in slope factor, Δ k, ≅ −2.5 mV), and a decreased maximum P o (from ∼0.82 to ∼0.47). Interestingly, channels inhibited by ethanol at low Ca2+ concentrations (2.5 μM) were very resistant to ethanol in the presence of increased Ca2+ (≥ 20 μM). Alcohol consumption in clinically relevant amounts may alter the contribution of maxi-K channels to the regulation of arterial tone.

scholarly journals Inhibitory effects of openers of large-conductance Ca2+-activated K+channels on agonist-induced phasic contractions in rabbit and mouse bronchial smooth muscle

2018 ◽  
Vol 315 (6) ◽  
pp. C818-C829 ◽  
Author(s):  
Eamonn Bradley ◽  
Roddy J. Large ◽  
Viktoriia Volodymyrivna Bihun ◽  
Nicolas D. Mullins ◽  
Mark A. Hollywood ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Airway Smooth Muscle ◽  
Racemic Mixture ◽  
Airway Smooth Muscle Cells ◽  
Inhibitory Effects ◽  
Bronchial Smooth Muscle ◽  
K Channels ◽  
Smooth Muscle Contractions ◽  
Inside Out

Airway smooth muscle expresses abundant BKCachannels, but their role in regulating contractions remains controversial. This study examines the effects of two potent BKCachannel openers on agonist-induced phasic contractions in rabbit and mouse bronchi. First, we demonstrated the ability of 10 μM GoSlo-SR5-130 to activate BKCachannels in inside-out patches from rabbit bronchial myocytes, where it shifted the activation V1/2by −88 ± 11 mV (100 nM Ca2+, n = 7). In mouse airway smooth muscle cells, GoSlo-SR5-130 dose dependently shifted V1/2by 12–83 mV over a concentration range of 1–30 μM. Compound X, a racemic mixture of two enantiomers, reported to be potent BKCachannel openers, shifted V1/2by 20–79 mV over a concentration range of 0.3–3 μM. In rabbit bronchial rings, exposure to histamine (1 μM) induced phasic contractions after a delay of ~35 min. These were abolished by GoSlo-SR5-130 (30 μM). Nifedipine (100 nM) and CaCCinhA01 (10 μM), a TMEM16A blocker, also abolished histamine-induced phasic contractions. In mouse bronchi, similar phasic contractions were evoked by exposure to U46619 (100 nM) and carbachol (100 nM). In each case, these were inhibited by concentrations of GoSlo-SR5-130 and compound X that shifted the activation V1/2of BKCachannels in the order of −80 mV. In conclusion, membrane potential-dependent regulation of L-type Ca2+channels appears to be important for histamine-, U46619-, and carbachol-induced phasic contractions in airway smooth muscle. Contractions can be abolished by BKCachannel openers, suggesting that these channels are potential targets for treating some causes of airway obstruction.

PKG-I alpha phosphorylates the alpha-subunit and upregulates reconstituted GKCa channels from tracheal smooth muscle

1995 ◽  
Vol 268 (6) ◽  
pp. L1057-L1063 ◽  
Author(s):  
A. Alioua ◽  
J. P. Huggins ◽  
E. Rousseau
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Smooth Muscles ◽  
Muscle Cells ◽  
Tracheal Smooth Muscle ◽  
Alpha Subunit ◽  
K Channel ◽  
Relative Molecular Mass ◽  
Airway Smooth Muscle Cells ◽  
Open Probability

Modulation of Ca(2+)-dependent K+ channel (GKCa) activities in airway smooth muscles (ASM) by guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (PKG) is thought to play a central role in mediating the effect of some bronchodilator agents that elevate cytoplasmic basal cGMP concentrations. However, no direct evidence supports this hypothesis in ASM. In the present work, we provide evidence that PKG-I alpha upregulates GKCa channels derived from bovine tracheal smooth muscle cells and reconstituted into planar lipid bilayers. In two different experimental approaches, PKG increased the open probability as well as the mean open time of GKCa channels, without any effect on unitary current amplitudes and unit conductance. Our results indicate that the kinetics of GKCa channels are controlled by a phosphorylation step mediated by PKG, and thus might be modulated by intracellular cGMP. Biochemical assays demonstrated that PKG phosphorylates several protein bands in the membrane fraction. Two of those proteins co-migrate with the same relative molecular mass as the 62- and 30-kDa components of the purified channel complex, identified as GKCa-alpha and -beta subunits, respectively. Our results also indicate that PKG phosphorylates the GKCa-alpha subunit with an apparent stoichiometry of 0.89, which would be consistent with the presence of a single PKG-sensitive phosphorylating site within its amino acid sequence. Furthermore, these results demonstrate for the first time that PKG directly phosphorylates GKCa from airway smooth muscle cells and thereby activates the channels at negative voltage or at low free Ca2+ concentrations.

Interaction of iberiotoxin with beta-adrenoceptor agonists and sodium nitroprusside on guinea pig trachea

1993 ◽  
Vol 74 (4) ◽  
pp. 1879-1884 ◽  
Author(s):  
T. R. Jones ◽  
L. Charette ◽  
M. L. Garcia ◽  
G. J. Kaczorowski
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Sodium Nitroprusside ◽  
Airway Smooth Muscle ◽  
Plasma Membranes ◽  
K Channel ◽  
K Channels ◽  
Beta Adrenoceptor ◽  
Adrenoceptor Agonists ◽  
Beta Adrenoceptor Agonists

Airway smooth muscle plasma membranes contain a variety of functional K+ channels. In particular, there is a predominance of Ca(2+)-activated K+ channels (maxi-K). Inhibition of these K+ channels has been postulated to account for the ability of charybdotoxin (ChTX) to produce contraction of airway smooth muscle and to modify the relaxant effects of beta-adrenoceptor agonists and sodium nitroprusside (SNP). Iberiotoxin (IbTX) is more selective and more potent than ChTX at blocking maxi-K channels. In this study, pharmacological experiments were performed on guinea pig trachea to determine whether IbTX produced effects similar to ChTX. The concentration-response curves to salbutamol were markedly affected by IbTX, with a > 60-fold rightward shift being produced with 20 nM IbTX. The maximal relaxation to salbutamol was reduced to 49.3 +/- 0.9, 22.3 +/- 4.7, and 15.0 +/- 2.7% of control maximum in the presence of 20, 60, and 180 nM IbTX, respectively. Similar to salbutamol, the maximal relaxation to SNP was reduced to 80 +/- 1.6, 19 +/- 1.7, and 12 +/- 2.1% of control maximum in the presence of 20, 60, and 180 nM IbTX, respectively. IbTX (180 nM) failed to produce a significant alteration of relaxation to the ATP-dependent K+ channel agonist BRL-34915. Exposure of tissues to K(+)-rich medium (80 mM) inhibited responses to salbutamol > or = SNP > isoproterenol. These results confirm and extend our earlier observations that maxi-K channels may be involved in regulating tone and relaxation of carbachol-contracted guinea pig tracheal smooth muscle. This mechanism is of particular importance for beta 2-adrenoceptor- and SNP-induced relaxation.

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