scholarly journals Myosin phosphorylation potentiates steady-state work output without altering contractile economy of mouse fast skeletal muscles

2017 ◽  
Vol 221 (2) ◽  
pp. jeb167742 ◽  
Author(s):  
William Gittings ◽  
Jordan Bunda ◽  
Rene Vandenboom
Keyword(s):  
Steady State ◽  
Skeletal Muscles ◽  
Work Output ◽  
Myosin Phosphorylation ◽  
Contractile Economy

Effects of substrate and inhibition of oxidative metabolism on contraction and myosin phosphorylation in ASM

1993 ◽  
Vol 264 (6) ◽  
pp. L553-L559 ◽  
Author(s):  
C. M. Hai ◽  
C. Watson ◽  
S. J. Wallach ◽  
V. Reyes ◽  
E. Kim ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Airway Smooth Muscle ◽  
Oxidative Metabolism ◽  
Energy Utilization ◽  
Atp Content ◽  
Active Stress ◽  
Myosin Phosphorylation ◽  
Intracellular Calcium Store ◽  
Cross Bridge

Steady-state active stress in smooth muscle is maintained by cross bridges which undergo continuous cycling and myosin phosphorylation, and the two processes both consume ATP. In this study, we investigated whether energy utilization by cross-bridge cycling and myosin phosphorylation is compartmentalized and examined their relative affinities for ATP in airway smooth muscle. We measured active stress, myosin phosphorylation, O2 consumption, and tissue ATP content in bovine tracheal smooth muscle activated by K+ depolarization when glucose was replaced by pyruvate and when oxidative metabolism was inhibited by hypoxia or uncoupled by 2,4-dinitrophenol. The results indicate that ATP produced from both glycolysis and oxidative metabolism is available to both cross-bridge cycling and myosin phosphorylation. However, steady-state myosin phosphorylation was insensitive to the inhibition of oxidative metabolism by hypoxia and mitochondrial uncoupling when steady-state isometric stress and tissue ATP content were significantly reduced. These results suggest that, relative to actomyosin adenosine 5'-triphosphatase, myosin light chain kinase has a higher affinity for ATP in intact airway smooth muscle. However, peak myosin phosphorylation associated with the initial rapid stress development was sensitive to inhibition of oxidative metabolism, probably reflecting a lower content of intracellular calcium store as a result of metabolic inhibition.

Role of myosin phosphorylation in contractility of a platelet aggregate

1985 ◽  
Vol 249 (3) ◽  
pp. C297-C303 ◽  
Author(s):  
M. E. Bromberg ◽  
R. W. Sevy ◽  
J. L. Daniel ◽  
L. Salganicoff
Keyword(s):  
Steady State ◽  
Light Chain ◽  
Myosin Phosphorylation ◽  
Nonmuscle Cells ◽  
Platelet Aggregate ◽  
Steady State Levels ◽  
State Contraction ◽  
The Relationship ◽  
Dose Dependent

The relationship between tension and myosin 20,000-Da light chain phosphorylation in intact nonmuscle cells was investigated using a preparation of thrombin-activated, irreversibly aggregated platelets known as the platelet strip. Steady-state levels of tension generated by the platelet strip were found to be linearly related to the level of myosin phosphorylation. This relationship was observed during dose-dependent relaxation induced by the adenylate cyclase activators prostaglandin (PG) E1 and PGI2, and during contraction induced by ADP, epinephrine, and the prostaglandin endoperoxide analogue U-46619, which did not appreciably alter the basal level of adenosine 3',5'-cyclic monophosphate in the preparation. The fully relaxed platelet strip, in the absence of external Ca2+, was associated with a level of 12% light chain phosphorylation, which increased to 72% on maximal contraction. During both relaxation and contraction, changes in myosin phosphorylation were also found to precede or coincide with tension changes. Furthermore, steady-state contraction induced by ADP was associated with a maintained elevation in the level of myosin phosphorylation. These results support the concept that myosin phosphorylation is an important regulatory mechanism for contractility in platelets.

cAMP, myosin dephosphorylation, and isometric relaxation of airway smooth muscle

1988 ◽  
Vol 64 (2) ◽  
pp. 705-709 ◽  
Author(s):  
P. de Lanerolle
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Muscle Relaxation ◽  
Fold Increase ◽  
Treatment Results ◽  
Myosin Phosphorylation ◽  
Temporal Relationships ◽  
Steady State Levels ◽  
Two Parameters ◽  
Camp Levels

The temporal relationships among increases in adenosine 3',5'-cyclic monophosphate (cAMP) levels, myosin dephosphorylation, and relaxation were investigated to clarify the mechanisms of airway muscle relaxation. Canine tracheal muscles isometrically contracted (82% of maximum force) with 10(-6) M methacholine were relaxed by adding either 4 x 10(-7) M atropine or 4 x 10(-5) M forskolin. Atropine had no effect on cAMP levels; myosin phosphorylation and force, however, decayed at the same rates and these two parameters returned to their basal pre-methacholine levels within 5 min. Forskolin treatment results in about a 10-fold increase in cAMP levels; myosin phosphorylation and force decayed simultaneously to their respective steady-state levels by 10 min but neither parameter returned to its pre-methacholine level. The addition of forskolin to muscles maximally contracted with 10(-4) M methacholine leads to about a 30-fold increase in cAMP levels. However, there are minimal decreases in myosin phosphorylation and force in these muscles. Thus myosin dephosphorylation appears to be essential for airway muscle relaxation, whereas an increase in cAMP in the absence of myosin dephosphorylation is insufficient to cause relaxation. Moreover, myosin dephosphorylation appears to be a common step in the cAMP-independent and cAMP-dependent mechanisms for airway muscle relaxation.

Cross-bridge phosphorylation and regulation of latch state in smooth muscle

1988 ◽  
Vol 254 (1) ◽  
pp. C99-C106 ◽  
Author(s):  
C. M. Hai ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Experimental Observation ◽  
Rate Constants ◽  
Regulatory Mechanism ◽  
Myosin Phosphorylation ◽  
Model Simulations ◽  
Cross Bridge ◽  
Cross Bridges ◽  
Latch State

We have developed a minimum kinetic model for cross-bridge interactions with the thin filament in smooth muscle. The model hypothesizes two types of cross-bridge interactions: 1) cycling phosphorylated cross bridges and 2) noncycling dephosphorylated cross bridges ("latch bridges"). The major assumptions are that 1) Ca2+-dependent myosin phosphorylation is the only postulated regulatory mechanism, 2) each myosin head acts independently, and 3) latch bridges are formed by dephosphorylation of an attached cross bridge. Rate constants were resolved by fitting data on the time courses of myosin phosphorylation and stress development. Comparison of the rate constants indicates that latch-bridge detachment is the rate-limiting step. Model simulations predicted a hyperbolic dependence of steady-state stress on myosin phosphorylation, which corresponded with the experimental observation of high values of stress with low levels of phosphorylation in intact tissues. Model simulations also predicted the experimental observation that an initial phosphorylation transient only accelerates stress development, with no effect on the final steady-state levels of stress. Because the only Ca2+-dependent regulatory mechanism in this model was activation of myosin light chain kinase, these results are consistent with the hypothesis that myosin phosphorylation is both necessary and sufficient for the development of the latch state.

scholarly journals Effect of guanosine triphosphate on the release and uptake of Ca2+ in saponin-permeabilized macrophages and the skeletal-muscle sarcoplasmic reticulum

1987 ◽  
Vol 242 (1) ◽  
pp. 253-260 ◽  
Author(s):  
T Hamachi ◽  
M Hirata ◽  
Y Kimura ◽  
T Ikebe ◽  
T Ishimatsu ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Polyethylene Glycol ◽  
Sarcoplasmic Reticulum ◽  
Sustained Release ◽  
Skeletal Muscles ◽  
Guanosine Triphosphate ◽  
Uptake Activity ◽  
Releasing Effect ◽  
Stimulation Of

The effects of GTP, with or without polyethylene glycol (PEG), on the release and uptake of Ca2+ were examined by using saponin-treated macrophages and sarcoplasmic reticulum isolated from skeletal muscles. The application of GTP in concentrations in the range 0.1-10 microM induced a gradual, small but sustained release of Ca2+ from the saponin-treated macrophages. The addition of PEG to GTP markedly enhanced the GTP-mediated Ca2+ release. GTP at the same concentration ranges used for Ca2+ release decreased the amount of Ca2+ uptake, at a steady state, but stimulated the rate of Ca2+ accumulation in the presence of oxalate, the Ca2+-precipitating anion. The addition of PEG abolished the GTP-evoked stimulation of Ca2+ accumulation in the presence of oxalate. The stimulating effect on the rate of Ca2+ accumulation by GTP and its elimination by PEG were not due to changes in the permeability of oxalate by either GTP or PEG, or both. The Ca2+-releasing effect of GTP without PEG was enhanced by eliminating the uptake activity by decreasing the content of ATP. These results indicate that GTP has an inherent activity to release Ca2+ from non-mitochondrial intracellular stores of saponin-treated macrophages, and PEG enhances the GTP-mediated Ca2+ release, partly owing to its eliminating effect on GTP-stimulated Ca2+ uptake activity. These effects of GTP observed with saponin-permeabilized macrophages were not apparent in the isolated skeletal-muscle sarcoplasmic reticulum.

Agonist-induced myosin phosphorylation during isometric contraction and unloaded shortening in airway smooth muscle

1992 ◽  
Vol 262 (1) ◽  
pp. L53-L62 ◽  
Author(s):  
C. M. Hai ◽  
B. Szeto
Keyword(s):  
Signal Transduction ◽  
Smooth Muscle ◽  
Steady State ◽  
Airway Smooth Muscle ◽  
Isometric Contraction ◽  
Airway Smooth Muscle Cell ◽  
Myosin Phosphorylation ◽  
Kinase C ◽  
Transduction Mechanisms ◽  
Muscle Cell Membrane

We measured myosin phosphorylation during isometric contraction at optimal length (Lo) and unloaded shortening induced by K(+)-depolarization, electrical stimulation, carbachol, histamine, and phorbol dibutyrate (PDB) in bovine trachealis. Peak myosin phosphorylation during unloaded shortening was lower than that during isometric contraction in response to all stimuli. The lower peak myosin phosphorylation during unloaded shortening appeared to be a stretch-sensitive response because myosin phosphorylation was either equally low or further reduced during the second unloaded shortening of preshortened tissues. Similar to peak myosin phosphorylation, steady-state myosin phosphorylation was also lower during unloaded shortening in carbachol-induced contractions. However, steady-state phosphorylation during unloaded shortening and isometric contraction were not significantly different in histamine- and PDB-induced contractions. Since the coupling between Ca2+ and myosin phosphorylation was not stretch sensitive, these results suggest the coexistence of stretch-sensitive and stretch-insensitive signal transduction mechanisms in the airway smooth muscle cell membrane, and the stretch-insensitive signal transduction mechanism might involve protein phosphorylation by protein kinase C.

Calcium dependence of myosin phosphorylation and airway smooth muscle contraction and relaxation

1986 ◽  
Vol 250 (4) ◽  
pp. C597-C604 ◽  
Author(s):  
W. T. Gerthoffer
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Dose Response ◽  
Time Course ◽  
Physiological Salt Solution ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Calcium Dependence ◽  
Contraction And Relaxation ◽  
Isotonic Shortening

The time course and the steady-state calcium dependence of myosin phosphorylation and isotonic shortening velocity were studied during contraction and relaxation of canine tracheal smooth muscle. Dephosphorylation of myosin coincided with the decay of isotonic shortening velocity during rapid relaxation following agonist washout. However, the decay of shortening velocity preceded dephosphorylation during a slow relaxation induced by Ca2+-free physiological salt solution (PSS). Carbachol dose-response curves for isometric stress development and myosin phosphorylation were superimposable but shifted to the left of the shortening velocity dose-response. The steady-state Ca2+ dependence of myosin phosphorylation was defined using carbachol and K+ as agonists. There was a significant dissociation of dephosphorylation and relaxation following a stepwise reduction of extracellular CaCl2 concentration. This result was related to muscarinic activation because the dissociation of relaxation and dephosphorylation was reduced by atropine in muscles stimulated with K+. Myosin phosphorylation was completely dissociated from contraction when muscles were stimulated with carbachol in Ca2+-free PSS and contracted by readmission of CaCl2. Mechanisms in addition to myosin phosphorylation appear to regulate airway muscle tone and shortening velocity, and two possibilities are discussed.

Sr2+ activates cross-bridge phosphorylation and latch state in smooth muscle

1988 ◽  
Vol 255 (3) ◽  
pp. C401-C407 ◽  
Author(s):  
C. M. Hai ◽  
R. A. Murphy
Keyword(s):  
Steady State ◽  
Induced Responses ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Stress Development ◽  
Cross Bridge ◽  
Induced Stress ◽  
Latch State ◽  
State Stress ◽  
Isotonic Shortening

Sr2+ induced myosin phosphorylation and stress development in both skinned and K+-depolarized, Ca2+-depleted, intact swine carotid media. Although higher concentrations of Sr2+ than Ca2+ were required for phosphorylation and stress development, the dependence of stress on phosphorylation was the same in intact tissues. K+ depolarization in the presence of 5 mM Sr2+ produced a transient in phosphorylation (53.2 +/- 5.1% at 1 min, falling to a steady-state value of 21.7 +/- 2.0%) in Ca2+-depleted tissues in which intracellular stores were refilled with Sr2+. Stress developed without a transient (T1/2 = 0.70 min) to a steady state of 89.7 +/- 2.0% of the stress induced by K+ depolarization in the presence of 1.6 mM Ca2+ (K-PSS). Cross-bridge cycling rate as measured by isotonic shortening velocity was proportional to myosin phosphorylation throughout the contraction. When intracellular stores were not refilled with Sr2+, phosphorylation rose to a sustained value of 28.8 +/- 2.7% and stress developed slowly (T1/2 = 2.9 min) to a steady state of 95.9 +/- 1.5% K-PSS-induced stress. Therefore, an initial phosphorylation transient induced by intracellular Sr2+ release only accelerated stress development without significant effects on steady-state stress or phosphorylation (as was true for Ca2+- induced responses). We concluded that Sr2+ substitutes for Ca2+ in phosphorylation and regulation of the latch state in the swine carotid media.

Phosphorylation of myosin in permeabilized mammalian cardiac and skeletal muscle cells

1986 ◽  
Vol 250 (4) ◽  
pp. C657-C660 ◽  
Author(s):  
H. L. Sweeney ◽  
J. T. Stull
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Muscle ◽  
Light Chain ◽  
Myosin Light Chain Kinase ◽  
Skeletal Muscles ◽  
Myosin Light Chain ◽  
Muscle Cells ◽  
Ventricular Muscle ◽  
Myosin Phosphorylation ◽  
Maximal Activation

The effect of myosin phosphorylation on tension production at less than 50% maximal activation by Ca2+ was examined in rabbit psoas and ventricular muscle. For psoas fibers, tension was determined at pCa 6.0, 5.8, 5.6, 5.5, and 5.4. Myosin light chain kinase (0.15 microM) and calmodulin (2 microM) were added, and the fibers were incubated at pCa 5.4, which resulted in an increase in light chain phosphorylation (P-light chain) from 5-10 to 60-75%. After 5 min, the sequence of pCa activations was repeated. An identical protocol was followed for cardiac muscle, except the activation solutions were pCa 6.2, 6.0, 5.9, 5.8, and 5.6. Phosphorylation of P-light chain increased tension in both permeabilized cardiac and skeletal muscle fibers. The effect manifested itself as a leftward shift in the pCa-tension relationship at levels below 50% maximal activation, with a decrease in the slope of the pCa-tension relationship. These results indicate that P-light chain phosphorylation affects actin-myosin interactions in cardiac and skeletal muscles at submaximal levels of Ca2+ activation

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