Inhibition of Ca2+-activated tension and myosin light chain phosphorylation in skinned smooth muscle strips by the phenothiazines

1980 ◽  
Vol 387 (2) ◽  
pp. 115-120 ◽  
Author(s):  
P. Cassidy ◽  
P. E. Hoar ◽  
W. G. L. Kerrick
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Myosin Light Chain Phosphorylation ◽  
Skinned Smooth Muscle

Effects of Ca2+, Mg2+, and myosin phosphorylation on skinned smooth muscle fibers

1987 ◽  
Vol 252 (5) ◽  
pp. C543-C554 ◽  
Author(s):  
R. J. Barsotti ◽  
M. Ikebe ◽  
D. J. Hartshorne
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Isometric Tension ◽  
Skinned Fibers ◽  
Myosin Light Chain Phosphorylation ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Chicken Gizzard ◽  
Skinned Smooth Muscle

Isometric tension, unloaded shortening velocity (Vus), and myosin light chain phosphorylation were measured with skinned chicken gizzard fibers at various Ca2+ concentrations and at two concentrations of free Mg2+, 0.7 and 2.2 mM. At low free Mg2+, an increase in Ca2+ from pCa 8.0 to 6.4 resulted in an increase of all three parameters. Between pCa 6.4 and 5.0, isometric tension and phosphorylation remained constant but Vus continued to increase. At low free Mg2+, therefore, Vus showed a dependence both on phosphorylation and on Ca2+. At high free Mg2+, tension and Vus increased as phosphorylation increased and both were maximum at pCa 6.4, where phosphorylation became constant. Therefore, at high free Mg2+, Vus was dependent only on phosphorylation and did not show an additional Ca2+ dependence. Incubation of the Ca2+-independent kinase (approximately 3 microM) with skinned fibers under various conditions resulted in a constant level of phosphorylation (49-58%). At high free Mg2+ plus the Ca2+-independent kinase Vus was independent of Ca2+, whereas at low free Mg2+ Vus increased from pCa 6.4 to 5.0. These data are consistent with the hypothesis that Ca2+ binding to the Ca2+-Mg2+ sites of myosin increase Vus and that this occurs at Ca2+ concentrations higher than those necessary to saturate calmodulin.

scholarly journals Arteriolar vasodilation involves actin depolymerization

2018 ◽  
Vol 315 (2) ◽  
pp. H423-H428
Author(s):  
Philip S. Clifford ◽  
Brian S. Ferguson ◽  
Jeffrey L. Jasperse ◽  
Michael A. Hill
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Sodium Nitroprusside ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Muscle Relaxation ◽  
Nitric Oxide Donor ◽  
Smooth Muscle Relaxation ◽  
Myosin Light Chain Phosphorylation ◽  
Actin Depolymerization

It is generally assumed that relaxation of arteriolar vascular smooth muscle occurs through hyperpolarization of the cell membrane, reduction in intracellular Ca2+ concentration, and activation of myosin light chain phosphatase/inactivation of myosin light chain kinase. We hypothesized that vasodilation is related to depolymerization of F-actin. Cremaster muscles were dissected in rats under pentobarbital sodium anesthesia (50 mg/kg). First-order arterioles were dissected, cannulated on glass micropipettes, pressurized, and warmed to 34°C. Internal diameter was monitored with an electronic video caliper. The concentration of G-actin was determined in flash-frozen intact segments of arterioles by ultracentrifugation and Western blot analyses. Arterioles dilated by ~40% of initial diameter in response to pinacidil (1 × 10−6 mM) and sodium nitroprusside (5 × 10−5 mM). The G-actin-to-smooth muscle 22α ratio was 0.67 ± 0.09 in arterioles with myogenic tone and increased significantly to 1.32 ± 0.34 ( P < 0.01) when arterioles were dilated with pinacidil and 1.14 ± 0.18 ( P < 0.01) with sodium nitroprusside, indicating actin depolymerization. Compared with control vessels (49 ± 5%), the percentage of phosphorylated myosin light chain was significantly reduced by pinacidil (24 ± 2%, P < 0.01) but not sodium nitroprusside (42 ± 4%). These findings suggest that actin depolymerization is an important mechanism for vasodilation of resistance arterioles to external agonists. Furthermore, pinacidil produces smooth muscle relaxation via both decreases in myosin light chain phosphorylation and actin depolymerization, whereas sodium nitroprusside produces smooth muscle relaxation primarily via actin depolymerization. NEW & NOTEWORTHY This article adds to the accumulating evidence on the contribution of the actin cytoskeleton to the regulation of vascular smooth muscle tone in resistance arterioles. Actin depolymerization appears to be an important mechanism for vasodilation of resistance arterioles to pharmacological agonists. Dilation to the K+ channel opener pinacidil is produced by decreases in myosin light chain phosphorylation and actin depolymerization, whereas dilation to the nitric oxide donor sodium nitroprusside occurs primarily via actin depolymerization. Listen to this article’s corresponding podcast at https://ajpheart.podbean.com/e/vascular-smooth-muscle-actin-depolymerization/ .

Mechanism of galanin-induced contraction of longitudinal smooth muscle of the rat jejunum

1998 ◽  
Vol 274 (2) ◽  
pp. G306-G313 ◽  
Author(s):  
Simon A. Ahtaridis ◽  
Surender S. Katoch ◽  
Robert S. Moreland
Keyword(s):  
Smooth Muscle ◽  
Pertussis Toxin ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Effective Concentration ◽  
Rat Jejunum ◽  
Myosin Light Chain Phosphorylation ◽  
Half Maximum ◽  
Longitudinal Smooth Muscle ◽  
Intracellular Ca

Intact and α-toxin-permeabilized longitudinal smooth muscle were mounted for measurement of force and myosin light chain phosphorylation. Galanin contracted intact jejunum with a half-maximum effective concentration of 9.2 ± 0.1 nM. Neither atropine, hexamethonium, guanethidine, nor tetrodotoxin affected the contraction. The contraction was also unaffected by depletion of intracellular Ca2+ or by addition of thapsigargin; removal of extracellular Ca2+ or addition of nifedipine abolished the contraction. Galanin increased myosin light chain phosphorylation levels concomitantly with force. During continued tissue stimulation, force fell to suprabasal values, whereas myosin light chain phosphorylation levels remained elevated. Galanin increased Ca2+ sensitivity of contraction in α-toxin-permeabilized tissues, and this was reversed by either guanosine 5′- O-(2-thiodiphosphate) or pertussis toxin. These results suggest that galanin-induced contraction of longitudinal jejunal smooth muscle is dependent on a pertussis toxin-sensitive G protein that is apparently not coupled to the release of intracellular Ca2+but to the influx of extracellular Ca2+ and involves an initial myofilament Ca2+ sensitization followed by Ca2+ desensitization.

Communication between tyrosine kinase pathway and myosin light chain kinase pathway in smooth muscle

1996 ◽  
Vol 271 (4) ◽  
pp. H1348-H1355 ◽  
Author(s):  
N. Jin ◽  
R. A. Siddiqui ◽  
D. English ◽  
R. A. Rhoades
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Tyrosine Kinase ◽  
Tyrosine Phosphorylation ◽  
Light Chain ◽  
Tyrosine Kinases ◽  
Myosin Light Chain ◽  
Smooth Muscle Contraction ◽  
Myosin Light Chain Phosphorylation ◽  
Kinase Pathway

Two separate signal transduction pathways exist in vascular smooth muscle: one for cell growth, proliferation, and differentiation and the other for contraction. Although activation of protein tyrosine kinases is intimately involved in the signaling pathway that induces cell growth, proliferation, and differentiation, activation of myosin light chain kinase (MLCK) is an important step in the pathway leading to smooth muscle contraction. Indirect evidence suggests that “cross talk” exists between these two signaling pathways, but the common intermediates are not well defined. The purpose of this study was to determine whether a vasoconstrictor and a mitogen initiate crossover signaling between the tyrosine kinase pathway and the MLCK pathway in vascular smooth muscle. Rat aorta and pulmonary arteries were isolated and stimulated with either fetal calf serum (FCS) or phenylephrine in the presence or absence of a tyrosine kinase inhibitor (genistein) or tyrosine phosphatase inhibitor [sodium o-vanadate (Na3 VO4)]. Isometric force was recorded as a function of time; myosin light chain phosphorylation, protein tyrosine phosphorylation, and mitogen-activated protein kinase (MAPK) mobility were determined by immunoblotting. The results demonstrate that FCS, which contains a variety of growth factors known to activate tyrosine kinases, induced myosin light chain phosphorylation and contraction in vascular smooth muscle. Phenylephrine, a vasoconstrictor known to activate MLCK, induced tyrosine phosphorylation of a 42-kDa protein identified as MAPK. Tyrosine phosphorylation of this protein was inhibited by genistein and enhanced by vanadate. Genistein significantly inhibited both serum- and phenylephrine-induced myosin light chain phosphorylation as well as the serum- and phenylephrine-induced force generation, whereas vanadate enhanced these responses. These data demonstrate interrelationship between activation of the tyrosine kinase pathway and the MLCK pathway in vascular smooth muscle. These interactions may influence smooth muscle contraction and be important in the regulation of smooth muscle cell proliferation.

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