Maternal dexamethasone treatment alters myosin isoform expression and contractile dynamics in fetal arteries

2002 ◽  
Vol 283 (5) ◽  
pp. H1743-H1749 ◽  
Author(s):  
Chi-Ming Hai ◽  
Grazyna Sadowska ◽  
Louise Francois ◽  
Barbara S. Stonestreet
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Myosin Light Chain ◽  
Carotid Arteries ◽  
Dexamethasone Treatment ◽  
Glucocorticoid Treatment ◽  
Relaxation Phase ◽  
Isoform Expression ◽  
Maternal Administration ◽  
Relaxation Rate Constant

We tested the hypothesis that maternal glucocorticoid treatment modulates 17-kDa myosin light chain (myosin LC17) isoform expression and contractile dynamics in fetal ovine carotid arteries. In the single course group, ewes received 6 mg dexamethasone or placebo over 48 h. In the repeated course group, ewes received 6 mg dexamethasone or placebo weekly for 5 wk. In response to 1 μM phenylephrine, arteries from fetuses of dexamethasone-treated ewes exhibited biphasic contractions, characterized by an intermediate relaxation phase. The relaxation rate constant was significantly higher in arteries from the fetuses of dexamethasone than placebo-treated ewes. The observed biphasic contractions suggest the appearance of functional sarcoplasmic reticulum in the arteries from the fetuses of dexamethasone-treated ewes. The myosin LC17a isoform expression was lower in the arteries from the fetuses of the placebo-treated ewes than in those from the ewes. Repeated maternal administration of dexamethasone induced an almost twofold increase in myosin LC17a isoform expression in the fetal arteries. In contrast, maternal myosin LC17a isoform expression was not affected by dexamethasone treatment. We speculate that dexamethasone-induced increases in fetal myosin LC17a isoform expression represent accelerated differentiation of a subpopulation of vascular smooth muscle cells from the fetal to adult phenotype.

Myosin dephosphorylation during rapid relaxation of hog carotid artery smooth muscle

1989 ◽  
Vol 256 (2) ◽  
pp. C315-C321 ◽  
Author(s):  
S. P. Driska ◽  
P. G. Stein ◽  
R. Porter
Keyword(s):  
Smooth Muscle ◽  
Carotid Artery ◽  
Rate Constant ◽  
Light Chain ◽  
Time Course ◽  
Myosin Light Chain ◽  
Force Development ◽  
Relaxation Phase ◽  
Rhythmic Contractions ◽  
Low Levels

Changes in myosin light chain phosphorylation were measured during histamine-induced rhythmic contractions of hog carotid artery smooth muscle strips. Histamine made the muscle strips contract spontaneously every 1-5 min, and this allowed measurement of the time course of phosphorylation in relation to force development under conditions where diffusion of the agonist through tissue would not complicate the interpretation of the data. In the absence of histamine, phosphorylation was low [0.12 +/- 0.04 mol P/mol of the 20,000-Da light chain (LC 20)]. Phosphorylation was slightly (but not significantly) higher in the presence of 10 microM histamine in the relaxed state between contractions (0.20 +/- 0.03 mol P/mol LC 20). In muscle strips frozen during force development, when force had reached half of its peak value, phosphorylation was 0.38 +/- 0.06 mol P/mol LC 20. The highest levels of phosphorylation (0.49 +/- 0.04 mol P/mol LC 20) were found in strips frozen at the peak of the rhythmic contractions. Strips frozen when force had declined to half of the peak force showed low levels of phosphorylation (0.17 +/- 0.07 mol P/mol LC 20), indicating that the myosin light chain phosphatase activity was quite high. Mathematical modeling of the kinase and phosphatase reactions suggested that the apparent first-order phosphatase rate constant was at least 0.08 s-1 under these conditions. To obtain a better estimate of this rate constant, a second series of phosphorylation measurements were made early in the relaxation phase of the rhythmic contractions. The highest phosphatase rate constant obtained from these measurements was 0.23 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Myosin light chain phosphorylation and tension development in stretch-activated arterial smooth muscle.

1984 ◽  
Vol 30 (12) ◽  
pp. 2063-2068 ◽  
Author(s):  
R F Ledvora ◽  
M Bárány ◽  
K Bárány
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Carotid Arteries ◽  
Chelating Agent ◽  
Prolonged Treatment ◽  
Light Chains ◽  
Active Tension ◽  
Two Dimensional Gel Electrophoresis ◽  
Tension Development

Abstract Phosphorylation of the 20 000-Da light chain of myosin in functionally different porcine carotid arteries was determined, with use of two-dimensional gel electrophoresis. Stretching arteries to 1.7 times their resting length resulted in maximal phosphorylation. Intracellular Ca2+ was mobilized for stretch-induced light chain phosphorylation. Releasing the stretch from the arteries produced active tension spontaneously, without the participation of any exogenous stimulating agent. Prolonged treatment of arteries with a chelating agent (EGTA) not only abolished stretch-induced phosphorylation, it also prevented the development of active tension when the stretch was released. However, when the EGTA was washed out and the strips were restretched and again released, the stretch-induced phosphorylation and the stretch-release-induced active tension were restored. Evidently, arteries must contain phosphorylated light chain if they are to produce active tension. The myosin light chain became partly dephosphorylated in arteries that developed active tension when the stretch was released, but more than half of the light chains remained phosphorylated. This result suggests that phosphorylation of light chain is involved, not in the generation of active tension, but rather in activation of smooth muscle.

Determinants of the contractile properties in the embryonic chicken gizzard and aorta

2000 ◽  
Vol 279 (6) ◽  
pp. C1722-C1732 ◽  
Author(s):  
Ozgur Ogut ◽  
Frank V. Brozovich
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Smooth Muscles ◽  
Contractile Properties ◽  
In Vitro Motility ◽  
Force Maintenance ◽  
Isoform Expression ◽  
Force Activation

Smooth muscle is generally grouped into two classes of differing contractile properties. Tonic smooth muscles show slow rates of force activation and relaxation and slow speeds of shortening ( V max) but force maintenance, whereas phasic smooth muscles show poor force maintenance but have fast V max and rapid rates of force activation and relaxation. We characterized the development of gizzard and aortic smooth muscle in embryonic chicks to identify the cellular determinants that define phasic (gizzard) and tonic (aortic) contractile properties. Early during development, tonic contractile properties are the default for both tissues. The gizzard develops phasic contractile properties between embryonic days ( ED) 12 and 20, characterized primarily by rapid rates of force activation and relaxation compared with the aorta. The rapid rate of force activation correlates with expression of the acidic isoform of the 17-kDa essential myosin light chain (MLC17a). Previous data from in vitro motility assays (Rover AS, Frezon Y, and Trybus KM. J Muscle Res Cell Motil 18: 103–110, 1997) have postulated that myosin heavy chain (MHC) isoform expression is a determinant for V max in intact tissues. In the current study, differences in V max did not correlate with previously published differences in MHC or MLC17a isoforms. Rather, V max was increased with thiophosphorylation of the 20-kDa regulatory myosin light chain (MLC20) in the gizzard, suggesting that a significant internal load exists. Furthermore, V max in the gizzard increased during postnatal development without changes in MHC or MLC17 isoforms. Although the rate of MLC20 phosphorylation was similar at ED 20, the rate of MLC20 dephosphorylation was significantly higher in the gizzard versus the aorta, correlating with expression of the M130 isoform of the myosin binding subunit in the myosin light chain phosphatase (MLCP) holoenzyme. These results indicate that unique MLCP and MLC17 isoform expression marks the phasic contractile phenotype.

Nitrovasodilators relax arterial smooth muscle by decreasing [Ca2+]i and uncoupling stress from myosin phosphorylation

1992 ◽  
Vol 263 (2) ◽  
pp. C461-C467 ◽  
Author(s):  
N. L. McDaniel ◽  
X. L. Chen ◽  
H. A. Singer ◽  
R. A. Murphy ◽  
C. M. Rembold
Keyword(s):  
Smooth Muscle ◽  
Myosin Light Chain ◽  
Carotid Arteries ◽  
Muscle Relaxation ◽  
Smooth Muscle Relaxation ◽  
Myosin Light Chain Phosphorylation ◽  
Arterial Smooth Muscle ◽  
Histamine Stimulation ◽  
Myosin Phosphorylation ◽  
Proportional Decrease

Elevations in guanosine 3',5'-cyclic monophosphate concentration ([cGMP]) are proposed to induce arterial smooth muscle relaxation by either 1) decreasing myoplasmic [Ca2+] ([Ca2+]i), 2) decreasing the [Ca2+]i sensitivity of phosphorylation, or 3) uncoupling force from myosin phosphorylation. We evaluated the importance of each of these mechanisms by measuring changes in [cGMP], aequorin- and fura-2-estimated [Ca2+]i, myosin light chain phosphorylation, and stress in histamine-stimulated swine carotid arteries. In tissues submaximally stimulated with 3 microM histamine, nitroprusside (NP) induced a proportional decrease in myoplasmic [Ca2+] and myosin phosphorylation, suggesting that the relaxation was at least partially induced by decreases in [Ca2+]i without a change in the [Ca2+]i sensitivity of phosphorylation. In tissues maximally stimulated with 10 microM histamine, NP and nitroglycerin produced significant relaxations that were not associated with significant sustained reductions in [Ca2+]i or myosin phosphorylation. With both submaximal and maximal histamine stimulation, nitrovasodilators produced more substantial relaxation than that expected from the nitrovasodilator-induced reduction in myosin phosphorylation. These results suggest that nitrovasodilators relax histamine-stimulated swine arterial smooth muscle by at least two mechanisms: 1) reducing [Ca2+]i, an effect observed in submaximally stimulated tissues, and 2) uncoupling of stress from myosin phosphorylation.

scholarly journals Contributions of VEGF to age-dependent transmural gradients in contractile protein expression in ovine carotid arteries

2011 ◽  
Vol 301 (3) ◽  
pp. C653-C666 ◽  
Author(s):  
Stacy M. Butler ◽  
Jenna M. Abrassart ◽  
Margaret C. Hubbell ◽  
Olayemi Adeoye ◽  
Andrew Semotiuk ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Light Chain ◽  
Relative Position ◽  
Myosin Light Chain ◽  
Carotid Arteries ◽  
Muscle Cells ◽  
Mrna Levels ◽  
Dependent Manner ◽  
Age Dependent

The present study explores the hypothesis that arterial smooth muscle cells are organized into layers with similar phenotypic characteristics that vary with the relative position between the lumen and the adventitia due to transmural gradients in vasotrophic factors. A corollary hypothesis is that vascular endothelial growth factor (VEGF) is a factor that helps establish transmural variations in smooth muscle phenotype. Organ culture of endothelium-denuded ovine carotid arteries with 3 ng/ml VEGF-A165 for 24 h differentially and significantly influenced potassium-induced (55% increase) and stretch-induced (36% decrease) stress-strain relations in adult ( n = 18) but not term fetal ( n = 21) arteries, suggesting that smooth muscle reactivity to VEGF is acquired during postnatal maturation. Because inclusion of fetal bovine serum significantly inhibited all contractile effects of VEGF (adult: n = 11; fetus: n = 11), it was excluded in all cultures. When assessed in relation to the distance between the lumen and the adventitia in immunohistochemically stained coronal artery sections, expression of smooth muscle α-actin (SMαA), myosin light chain kinase (MLCK), and 20-kDa regulatory myosin light chain exhibited distinct protein-dependent and age-dependent gradients across the artery wall. VEGF depressed regional SMαA abundance up to 15% in adult ( n = 6) but not in fetal ( n = 6) arteries, increased regional MLCK abundance up to 140% in fetal ( n = 8) but not in adult ( n = 10) arteries, and increased regional MLC20 abundance up to 28% in fetal arteries ( n = 7) but decreased it by 17% in adult arteries ( n = 9). Measurements of mRNA levels verified that VEGF receptor transcripts for both Flt-1 and kinase insert domain receptor (KDR) were expressed in both fetal and adult arteries. Overall, the present data support the unique hypothesis that smooth muscle cells are organized into lamina of similar phenotype with characteristics that depend on the relative position between the lumen and the adventitia and involve the direct effects of growth factors such as VEGF, which acts independently of the vascular endothelium in an age-dependent manner.

Electron Probe Analysis of Muscle

1982 ◽  
Vol 40 ◽  
pp. 398-401
Author(s):  
A. V. Somlyo ◽  
H. Shuman ◽  
A. P. Somlyo
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Resting State ◽  
Binding Sites ◽  
Electron Probe ◽  
Frog Skeletal Muscle ◽  
Electron Probe Analysis ◽  
Probe Analysis

Electron probe analysis of frozen dried cryosections of frog skeletal muscle, rabbit vascular smooth muscle and of isolated, hyperpermeab1 e rabbit cardiac myocytes has been used to determine the composition of the cytoplasm and organelles in the resting state as well as during contraction. The concentration of elements within the organelles reflects the permeabilities of the organelle membranes to the cytoplasmic ions as well as binding sites. The measurements of [Ca] in the sarcoplasmic reticulum (SR) and mitochondria at rest and during contraction, have direct bearing on their role as release and/or storage sites for Ca in situ.

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