scholarly journals Augmented KCa2.3 Channel Feedback Regulation of Oxytocin Stimulated Uterine Strips from Nonpregnant Mice

2021 ◽  
Vol 22 (24) ◽  
pp. 13585
Author(s):  
Megan Zak ◽  
Bri Kestler ◽  
Trudy Cornwell ◽  
Mark S. Taylor
Keyword(s):  
Smooth Muscle ◽  
Isometric Force ◽  
Significant Risk ◽  
Feedback Regulation ◽  
Cyclopiazonic Acid ◽  
Uterine Contractions ◽  
Close Proximity ◽  
Force Myography ◽  
Channel Feedback ◽  
New Strategies

Uterine contractions prior to 37 weeks gestation can result in preterm labor with significant risk to the infant. Current tocolytic therapies aimed at suppressing premature uterine contractions are largely ineffective and cause serious side effects. Calcium (Ca2+) dependent contractions of uterine smooth muscle are physiologically limited by the opening of membrane potassium (K+) channels. Exploiting such inherent negative feedback mechanisms may offer new strategies to delay labor and reduce risk. Positive modulation of small conductance Ca2+-activated K+ (KCa2.3) channels with cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA), effectively decreases uterine contractions. This study investigates whether the receptor agonist oxytocin might solicit KCa2.3 channel feedback that facilitates CyPPA suppression of uterine contractions. Using isometric force myography, we found that spontaneous phasic contractions of myometrial tissue from nonpregnant mice were suppressed by CyPPA and, in the presence of CyPPA, oxytocin failed to augment contractions. In tissues exposed to oxytocin, depletion of internal Ca2+ stores with cyclopiazonic acid (CPA) impaired CyPPA relaxation, whereas blockade of nonselective cation channels (NSCC) using gadolinium (Gd3+) had no significant effect. Immunofluorescence revealed close proximity of KCa2.3 channels and ER inositol trisphosphate receptors (IP3Rs) within myometrial smooth muscle cells. The findings suggest internal Ca2+ stores play a role in KCa2.3-dependent feedback control of uterine contraction and offer new insights for tocolytic therapies.

scholarly journals Mechanical signals and mechanosensitive modulation of intracellular [Ca2+] in smooth muscle

2000 ◽  
Vol 279 (5) ◽  
pp. C1375-C1384 ◽  
Author(s):  
Steven S. An ◽  
Chi-Ming Hai
Keyword(s):  
Smooth Muscle ◽  
Isometric Force ◽  
Muscle Length ◽  
Cyclopiazonic Acid ◽  
Underlying Mechanism ◽  
Optimal Length ◽  
Mechanical Signal ◽  
Intracellular Ca ◽  
Data Points ◽  
Isotonic Shortening

We tested the hypothesis that strain is the primary mechanical signal in the mechanosensitive modulation of intracellular Ca2+concentration ([Ca2+]i) in airway smooth muscle. We found that [Ca2+]i was significantly correlated with muscle length during isotonic shortening against 20% isometric force (Fiso). When the isotonic load was changed to 50% Fiso, data points from the 20 and 50% Fiso experiments overlapped in the length-[Ca2+]i relationship. Similarly, data points from the 80% Fiso experiments clustered near those from the 50% Fiso experiments. Therefore, despite 2.5- and 4-fold differences in external load, [Ca2+]idid not deviate much from the length-[Ca2+]irelation that fitted the 20% Fiso data. Maximal inhibition of sarcoplasmic reticular (SR) Ca2+ uptake by 10 μM cyclopiazonic acid (CPA) did not significantly change [Ca2+]i in carbachol-induced isometric contractions and isotonic shortening. CPA also did not significantly change myosin light-chain phosphorylation or force redevelopment when carbachol-activated muscle strips were quickly released from optimal length ( L o) to 0.5 L o. These results are consistent with the hypothesis and suggest that SR Ca2+ uptake is not the underlying mechanism.

scholarly journals CyPPA, a positive modulator of small-conductance Ca2+-activated K+ channels, inhibits phasic uterine contractions and delays preterm birth in mice

2011 ◽  
Vol 301 (5) ◽  
pp. C1027-C1035 ◽  
Author(s):  
Dana V. Skarra ◽  
Trudy Cornwell ◽  
Viktoriya Solodushko ◽  
Amber Brown ◽  
Mark S. Taylor
Keyword(s):  
Smooth Muscle ◽  
Preterm Birth ◽  
Preterm Labor ◽  
Feedback Regulation ◽  
Fold Increase ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Negative Feedback Regulation ◽  
Uterine Contractions ◽  
Small Conductance

Organized uterine contractions, including those necessary for parturition, are dependent on calcium entry through voltage-gated calcium channels in myometrial smooth muscle cells. Recent evidence suggests that small-conductance Ca2+-activated potassium channels (KCa2), specifically isoforms KCa2.2 and 2.3, may control these contractions through negative feedback regulation of Ca2+ entry. We tested whether selective pharmacologic activation of KCa2.2/2.3 channels might depress uterine contractions, providing a new strategy for preterm labor intervention. Western blot analysis and immunofluorescence microscopy revealed expression of both KCa2.2 and KCa2.3 in the myometrium of nonpregnant (NP) and pregnant (gestation day 10 and 16; D10 and D16, respectively) mice. Spontaneous phasic contractions of isolated NP, D10, and D16 uterine strips were all suppressed by the KCa2.2/2.3-selective activator CyPPA in a concentration-dependent manner. This effect was antagonized by the selective KCa2 inhibitor apamin. Whereas CyPPA sensitivity was reduced in D10 and D16 versus NP strips (pIC50 5.33 ± 0.09, 4.64 ± 0.03, 4.72 ± 0.10, respectively), all contractions were abolished between 30 and 60 μM. Blunted contractions were associated with CyPPA depression of spontaneous Ca2+ events in myometrial smooth muscle bundles. Augmentation of uterine contractions with oxytocin or prostaglandin F2α did not reduce CyPPA sensitivity or efficacy. Finally, in an RU486-induced preterm labor model, CyPPA significantly delayed time to delivery by 3.4 h and caused a 2.5-fold increase in pup retention. These data indicate that pharmacologic stimulation of myometrial KCa2.2/2.3 channels effectively suppresses Ca2+-mediated uterine contractions and delays preterm birth in mice, supporting the potential utility of this approach in tocolytic therapies.

Mechanisms of Direct Inhibitory Action of Isoflurane on Vascular Smooth Muscle of Mesenteric Resistance Arteries

2003 ◽  
Vol 99 (3) ◽  
pp. 666-677 ◽  
Author(s):  
Takashi Akata ◽  
Tomoo Kanna ◽  
Jun Yoshino ◽  
Shosuke Takahashi
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Vascular Reactivity ◽  
Channel Blocker ◽  
Isometric Force ◽  
Systemic Resistance ◽  
Resistance Arteries ◽  
Voltage Gated ◽  
Fura 2 ◽  
Force Relation

Background Isoflurane has been shown to directly inhibit vascular reactivity. However, less information is available regarding its underlying mechanisms in systemic resistance arteries. Methods Endothelium-denuded smooth muscle strips were prepared from rat mesenteric resistance arteries. Isometric force and intracellular Ca2+ concentration ([Ca2+]i) were measured simultaneously in the fura-2-loaded strips, whereas only the force was measured in the beta-escin membrane-permeabilized strips. Results Isoflurane (3-5%) inhibited the increases in both [Ca2+]i and force induced by either norepinephrine (0.5 microM) or KCl (40 mM). These inhibitions were similarly observed after depletion of intracellular Ca2+ stores by ryanodine. Regardless of the presence of ryanodine, after washout of isoflurane, its inhibition of the norepinephrine response (both [Ca2+]i and force) was significantly prolonged, whereas that of the KCl response was quickly restored. In the ryanodine-treated strips, the norepinephrine- and KCl-induced increases in [Ca2+]i were both eliminated by nifedipine, a voltage-gated Ca2+ channel blocker, whereas only the former was inhibited by niflumic acid, a Ca2+-activated Cl- channel blocker. Isoflurane caused a rightward shift of the Ca2+-force relation only in the fura-2-loaded strips but not in the beta-escin-permeabilized strips. Conclusions In mesenteric resistance arteries, isoflurane depresses vascular smooth muscle reactivity by directly inhibiting both Ca2+ mobilization and myofilament Ca2+ sensitivity. Isoflurane inhibits both norepinephrine- and KCl-induced voltage-gated Ca2+ influx. During stimulation with norepinephrine, isoflurane may prevent activation of Ca2+-activated Cl- channels and thereby inhibit voltage-gated Ca2+ influx in a prolonged manner. The presence of the plasma membrane appears essential for its inhibition of the myofilament Ca2+ sensitivity.

Functional coupling between the Na+/Ca2+ exchanger and nonselective cation channels during histamine stimulation in guinea pig tracheal smooth muscle

2007 ◽  
Vol 293 (1) ◽  
pp. L191-L198 ◽  
Author(s):  
Paola Algara-Suárez ◽  
Catalina Romero-Méndez ◽  
Tom Chrones ◽  
Sergio Sánchez-Armass ◽  
Ulises Meza ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Force Measurement ◽  
Isometric Force ◽  
Sustained Response ◽  
Functional Coupling ◽  
Channel Activation ◽  
Histamine Stimulation ◽  
Nonselective Cation Channels ◽  
Intracellular Ca

Airway smooth muscle (ASM) contracts partly due to an increase in cytosolic Ca2+. In this work, we found that the contraction caused by histamine depends on external Na+, possibly involving nonselective cationic channels (NSCC) and the Na+/Ca2+ exchanger (NCX). We performed various protocols using isometric force measurement of guinea pig tracheal rings stimulated by histamine. We observed that force reached 53 ± 1% of control during external Na+ substitution by N-methyl-d-glucamine+, whereas substitution by Li+ led to no significant change (91 ± 1%). Preincubation with KB-R7943 decreased the maximal force developed (52.3 ± 5.6%), whereas preincubation with nifedipine did not (89.7 ± 1.8%). Also, application of the nonspecific NCX blocker KB-R7943 and nifedipine on histamine-precontracted tracheal rings reduced force to 1 ± 3%, significantly different from nifedipine alone (49 ± 6%). Moreover, nonspecific NSCC inhibitors SKF-96365 and 2-aminoethyldiphenyl borate reduced force to 1 ± 1% and 19 ± 7%, respectively. Intracellular Ca2+ measurements in isolated ASM cells showed that KB-R7943 and SKF-96365 reduced the peak and sustained response to histamine (0.20 ± 0.1 and 0.19 ± 0.09 for KB-R, 0.43 ± 0.16 and 0.47 ± 0.18 for SKF, expressed as mean of differences). Moreover, Na+-free solution only inhibited the sustained response (0.54 ± 0.25). These data support an important role for NSCC and NCX during histamine stimulation. We speculate that histamine induces Na+ influx through NSCC that promotes the Ca2+ entry mode of NCX and CaV1.2 channel activation, thereby causing contraction.

scholarly journals The Na,K-ATPase-Dependent Src Kinase Signaling Changes with Mesenteric Artery Diameter

2018 ◽  
Vol 19 (9) ◽  
pp. 2489 ◽  
Author(s):  
Lin Zhang ◽  
Christian Aalkjaer ◽  
Vladimir Matchkov
Keyword(s):  
Smooth Muscle ◽  
Binding Sites ◽  
Isometric Force ◽  
Src Kinase ◽  
Ouabain Binding ◽  
Arterial Diameter ◽  
Small Arteries ◽  
Functional Changes ◽  
High Affinity ◽  
Different Diameters

Inhibition of the Na,K-ATPase by ouabain potentiates vascular tone and agonist-induced contraction. These effects of ouabain varies between different reports. In this study, we assessed whether the pro-contractile effect of ouabain changes with arterial diameter and the molecular mechanism behind it. Rat mesenteric small arteries of different diameters (150–350 µm) were studied for noradrenaline-induced changes of isometric force and intracellular Ca2+ in smooth muscle cells. These functional changes were correlated to total Src kinase and Src phosphorylation assessed immunohistochemically. High-affinity ouabain-binding sites were semi-quantified with fluorescent ouabain. We found that potentiation of noradrenaline-sensitivity by ouabain correlates positively with an increase in arterial diameter. This was not due to differences in intracellular Ca2+ responses but due to sensitization of smooth muscle cell contractile machinery to Ca2+. This was associated with ouabain-induced Src activation, which increases with increasing arterial diameter. Total Src expression was similar in arteries of different diameters but the density of high-affinity ouabain binding sites increased with increasing arterial diameters. We suggested that ouabain binding induces more Src kinase activity in mesenteric small arteries with larger diameter leading to enhanced sensitization of the contractile machinery to Ca2+.

Myosin thick filament lability induced by mechanical strain in airway smooth muscle

2001 ◽  
Vol 90 (5) ◽  
pp. 1811-1816 ◽  
Author(s):  
Kuo-Hsing Kuo ◽  
Lu Wang ◽  
Peter D. Paré ◽  
Lincoln E. Ford ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Cross Sections ◽  
Structural Changes ◽  
Isometric Force ◽  
Mechanical Strain ◽  
Thick Filament ◽  
Functional Changes ◽  
Thick Filaments ◽  
Length Changes

Airway smooth muscle adapts to different lengths with functional changes that suggest plastic alterations in the filament lattice. To look for structural changes that might be associated with this plasticity, we studied the relationship between isometric force generation and myosin thick filament density in cell cross sections, measured by electron microscope, after length oscillations applied to the relaxed porcine trachealis muscle. Muscles were stimulated regularly for 12 s every 5 min. Between two stimulations, the muscles were submitted to repeated passive ±30% length changes. This caused tetanic force and thick-filament density to fall by 21 and 27%, respectively. However, in subsequent tetani, both force and filament density recovered to preoscillation levels. These findings indicate that thick filaments in airway smooth muscle are labile, depolymerization of the myosin filaments can be induced by mechanical strain, and repolymerization of the thick filaments underlies force recovery after the oscillation. This thick-filament lability would greatly facilitate plastic changes of lattice length and explain why airway smooth muscle is able to function over a large length range.

Mechanisms of cyclic nucleotide-induced relaxation in canine tracheal smooth muscle

1995 ◽  
Vol 268 (3) ◽  
pp. L407-L413 ◽  
Author(s):  
I. McGrogan ◽  
S. Lu ◽  
S. Hipworth ◽  
L. Sormaz ◽  
R. Eng ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Cyclic Nucleotide ◽  
Cyclopiazonic Acid ◽  
Inhibitory Effect ◽  
Beta Agonist ◽  
Cyclic Monophosphate ◽  
Median Effective Concentration ◽  
Camp Levels ◽  
Ca2 Channels

The effects of exogeneous cyclopiazonic acid (CPA, 10 microM), a selective inhibitor of the sarcoplasmic reticulum (SR) Ca2+ adenosinetriphosphatase, on cyclic nucleotide-induced relaxations of canine airway smooth muscle were examined. Strips of tracheal muscle were precontracted with carbachol (50% median effective concentration, 0.1 microM) or with 60 mM KCl. The beta-agonist isoproterenol (ISO, 10 microM) relaxed the tissue by approximately 50%. The relaxation was reduced in the presence of CPA when L-type Ca2+ channels were available but not when these were blocked by 0.1 microM nifedipine. Forskolin (1.0 microM), an adenylate cyclase activator, was less effective at inhibiting the contraction than ISO, and addition of CPA did not block its inhibitory effect as effectively as when ISO was used. Radioimmunoassay indicated that both these agents raised adenosine 3',5'-cyclic monophosphate (cAMP) levels to the same degree. Very little relaxation of the precontracted smooth muscle was elicited by 3 mM 8-bromo-adenosine 3',5'-cyclic monophosphate (8-BrcAMP), and addition of CPA had no effect. Sodium nitroprusside (100 microM) and 8-bromo-guanosine 3',5'-cyclic monophosphate (10 mM) inhibited contraction to a greater degree than any agent that raised cAMP. These inhibitions were greatly reduced in the presence of CPA when L-type Ca2+ channels were available. We conclude that pumping of Ca2+ into SR plays a major role guanosine 3',5'-cyclic monophosphate-produced but not cAMP-induced relaxation; L-type Ca2+ channels must be available for the relaxant role of Ca2+ pumping into the SR to be expressed; and ISO-induced relaxation may not involve primarily elevation of the cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of Rho/ROCK signaling in airway smooth muscle by membrane potential and [Ca2+]i

2005 ◽  
Vol 289 (4) ◽  
pp. L574-L582 ◽  
Author(s):  
Caiqiong Liu ◽  
Jianmin Zuo ◽  
Evi Pertens ◽  
Peter B. Helli ◽  
Luke J. Janssen
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase ◽  
Signal Transduction Pathway ◽  
Cyclopiazonic Acid ◽  
Membrane Depolarization ◽  
Rock Inhibitor ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
G Protein Coupled ◽  
Evoked Contractions

Recently, we have shown that Rho and Rho-activated kinase (ROCK) may become activated by high-millimolar KCl, which had previously been widely assumed to act solely through opening of voltage-dependent Ca2+ channels. In this study, we explored in more detail the relationship between membrane depolarization, Ca2+ currents, and activation of Rho/ROCK in bovine tracheal smooth muscle. Ca2+ currents began to activate at membrane voltages more positive than −40 mV and were maximally activated above 0 mV; at the same time, these underwent time- and voltage-dependent inactivation. Depolarizing intact tissues by KCl challenge evoked contractions that were blocked equally, and in a nonadditive fashion, by nifedipine or by the ROCK inhibitor Y-27632. Other agents that elevate intracellular calcium concentration ([Ca2+]i) by pathways independent of G protein-coupled receptors, namely the SERCA-pump inhibitor cyclopiazonic acid and the Ca2+ ionophore A-23187, evoked contractions that were also largely reduced by Y-27632. KCl directly increased Rho and ROCK activities in a concentration-dependent fashion that paralleled closely the effect of KCl on tone and [Ca2+]i, as well as the voltage-dependent Ca2+ currents that were measured over the voltage ranges that are evoked by 0–120 mM KCl. Through the use of various pharmacological inhibitors, we ruled out roles for Ca2+/calmodulin-dependent CaM kinase II, protein kinase C, and protein kinase A in mediating the KCl-stimulated changes in tone and Rho/ROCK activities. In conclusion, Rho is activated by elevation of [Ca2+]i (although the signal transduction pathway underlying this Ca2+ dependence is still unclear) and possibly also by membrane depolarization per se.

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