Slowly cycling Rho kinase-dependent actomyosin cross-bridge “slippage” explains intrinsic high compliance of detrusor smooth muscle

Biological soft tissues are viscoelastic because they display time-independent pseudoelasticity and time-dependent viscosity. However, there is evidence that the bladder may also display plasticity, defined as an increase in strain that is unrecoverable unless work is done by the muscle. In the present study, an electronic lever was used to induce controlled changes in stress and strain to determine whether rabbit detrusor smooth muscle (rDSM) is best described as viscoelastic or viscoelastic plastic. Using sequential ramp loading and unloading cycles, stress-strain and stiffness-stress analyses revealed that rDSM displayed reversible viscoelasticity, and that the viscous component was responsible for establishing a high stiffness at low stresses that increased only modestly with increasing stress compared with the large increase produced when the viscosity was absent and only pseudoelasticity governed tissue behavior. The study also revealed that rDSM underwent softening correlating with plastic deformation and creep that was reversed slowly when tissues were incubated in a Ca2+-containing solution. Together, the data support a model of DSM as a viscoelastic-plastic material, with the plasticity resulting from motor protein activation. This model explains the mechanism of intrinsic bladder compliance as “slipping” cross bridges, predicts that wall tension is dependent not only on vesicle pressure and radius but also on actomyosin cross-bridge activity, and identifies a novel molecular target for compliance regulation, both physiologically and therapeutically.

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272 RHO-KINASE PATHWAY DIMINISHES THE RELAXATION EFFECT OF CYCLIC ADENOSINE MONOPHOSPHATE ON CARBACHOL-INDUCED CALCIUM SENSITIZATION IN CONTRACTION OF HUMAN DETRUSOR SMOOTH MUSCLE

The Journal of Urology ◽

10.1016/j.juro.2012.02.329 ◽

2012 ◽

Vol 187 (4S) ◽

Author(s):

Nouval Shahab ◽

Shunichi Kajioka ◽

Maya Hayashi ◽

Takakazu Yunoki ◽

Seiji Naito

Keyword(s):

Smooth Muscle ◽

Rho Kinase ◽

Cyclic Adenosine Monophosphate ◽

Relaxation Effect ◽

Adenosine Monophosphate ◽

Detrusor Smooth Muscle ◽

Calcium Sensitization ◽

Human Detrusor ◽

Kinase Pathway

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Reversible plasticity of detrusor smooth muscle: evidence for a key role of “slipping” actomyosin cross-bridges in the control of urinary bladder compliance

AJP Renal Physiology ◽

10.1152/ajprenal.00227.2017 ◽

2017 ◽

Vol 313 (4) ◽

pp. F862-F863

Author(s):

Thomas J. Eddinger

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Detrusor Smooth Muscle ◽

Bladder Compliance ◽

Cross Bridges

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Cooperative attachment of cross bridges predicts regulation of smooth muscle force by myosin phosphorylation

AJP Cell Physiology ◽

10.1152/ajpcell.00082.2004 ◽

2004 ◽

Vol 287 (3) ◽

pp. C594-C602 ◽

Cited By ~ 35

Author(s):

Christopher M. Rembold ◽

Robert L. Wardle ◽

Christopher J. Wingard ◽

Timothy W. Batts ◽

Elaine F. Etter ◽

...

Keyword(s):

Skeletal Muscle ◽

Smooth Muscle ◽

Time Course ◽

Muscle Force ◽

Regulatory System ◽

Force Development ◽

Cross Bridge ◽

Cross Bridges ◽

The Relationship ◽

Cooperative Activation

Serine 19 phosphorylation of the myosin regulatory light chain (MRLC) appears to be the primary determinant of smooth muscle force development. The relationship between MRLC phosphorylation and force is nonlinear, showing that phosphorylation is not a simple switch regulating the number of cycling cross bridges. We reexamined the MRLC phosphorylation-force relationship in slow, tonic swine carotid media; fast, phasic rabbit urinary bladder detrusor; and very fast, tonic rat anococcygeus. We found a sigmoidal dependence of force on MRLC phosphorylation in all three tissues with a threshold for force development of ∼0.15 mol Pi/mol MRLC. This behavior suggests that force is regulated in a highly cooperative manner. We then determined whether a model that employs both the latch-bridge hypothesis and cooperative activation could reproduce the relationship between Ser19-MRLC phosphorylation and force without the need for a second regulatory system. We based this model on skeletal muscle in which attached cross bridges cooperatively activate thin filaments to facilitate cross-bridge attachment. We found that such a model describes both the steady-state and time-course relationship between Ser19-MRLC phosphorylation and force. The model required both cooperative activation and latch-bridge formation to predict force. The best fit of the model occurred when binding of a cross bridge cooperatively activated seven myosin binding sites on the thin filament. This result suggests cooperative mechanisms analogous to skeletal muscle that will require testing.

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Regulation of shortening velocity by cross-bridge phosphorylation in smooth muscle

AJP Cell Physiology ◽

10.1152/ajpcell.1988.255.1.c86 ◽

1988 ◽

Vol 255 (1) ◽

pp. C86-C94 ◽

Cited By ~ 118

Author(s):

C. M. Hai ◽

R. A. Murphy

Keyword(s):

Smooth Muscle ◽

Shortening Velocity ◽

Internal Load ◽

Cross Bridge ◽

Bridge Model ◽

The Family ◽

Cross Bridges ◽

Latch State ◽

The Relationship ◽

State Stress

We have proposed a model that incorporates a dephosphorylated "latch bridge" to explain the mechanics and energetics of smooth muscle. Cross-bridge phosphorylation is proposed as a prerequisite for cross-bridge attachment and rapid cycling. Features of the model are 1) myosin light chain kinase and phosphatase can act on both free and attached cross bridges, 2) dephosphorylation of an attached phosphorylated cross bridge produces a noncycling "latch bridge," and 3) latch bridges have a slow detachment rate. This model quantitatively predicts the latch state: stress maintenance with reduced phosphorylation, cross-bridge cycling rates, and ATP consumption. In this study, we adapted A. F. Huxley's formulation of crossbridge cycling (A. F. Huxley, Progr. Biophys. Mol. Biol. 7: 255-318, 1957) to the latch-bridge model to predict the relationship between isotonic shortening velocity and phosphorylation. The model successfully predicted the linear dependence of maximum shortening velocity at zero external load (V0) on phosphorylation, as well as the family of stress-velocity curves determined at different times during a contraction when phosphorylation values varied. The model implies that it is unnecessary to invoke an internal load or multiple regulatory mechanisms to explain regulation of V0 in smooth muscle.

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Dependence of stress on cross-bridge phosphorylation in vascular smooth muscle

AJP Cell Physiology ◽

10.1152/ajpcell.1989.256.1.c96 ◽

1989 ◽

Vol 256 (1) ◽

pp. C96-C100 ◽

Cited By ~ 43

Author(s):

P. H. Ratz ◽

C. M. Hai ◽

R. A. Murphy

Keyword(s):

Smooth Muscle ◽

Steady State ◽

Vascular Smooth Muscle ◽

Light Chain ◽

Phorbol Esters ◽

Receptor Activation ◽

Bay K 8644 ◽

Cross Bridge ◽

Cross Bridges ◽

State Stress

Cross-bridge phosphorylation associated with agonist-stimulated contraction of vascular smooth muscle is often transiently elevated. Such observations led to the concept that phosphorylation of the 20-kDa myosin regulatory light chain (Mp) was required for initial activation and cross-bridge cycling but might not be necessary for steady-state maintenance of stress in the latch state. The possibility that stress maintenance is not regulated by phosphorylation has received some experimental support in contractions induced by phorbol esters and the calcium channel activator BAY K 8644 in which significant increases in Mp were not detected. Our aim was to test the hypothesis that phosphorylation is both necessary and sufficient for activation and for maintenance of steady-state stress. Activation of swine carotid media using agents that bypass receptor activation and elevate Ca2+ influx without mobilizing intracellular Ca2+ stores (BAY K 8644 and ionomycin) produced monotonic increases in both stress and Mp. Transient initial peaks in Mp were absent. Steady-state stress induced by both receptor- and nonreceptor-mediated activation was dependent on small increases in Mp. Increases in Mp greater than 0.3 mol Pi/mol myosin light chain had small effects on stress but produced large increases in the maximum rate of cross-bridge cycling at zero load (Vo). The experimentally determined dependence of stress on Mp was quantitatively predicted by our working hypothesis. This model proposes that Ca2+-stimulated cross-bridge phosphorylation is obligatory for cross-bridge attachment. However, dephosphorylation of attached cross bridges to form noncycling "latch bridges" allows stress maintenance with reduced Mp and cycling.

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Series-to-parallel transition in the filament lattice of airway smooth muscle

Journal of Applied Physiology ◽

10.1152/jappl.2000.89.3.869 ◽

2000 ◽

Vol 89 (3) ◽

pp. 869-876 ◽

Cited By ~ 80

Author(s):

Chun Y. Seow ◽

Victor R. Pratusevich ◽

Lincoln E. Ford

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Muscle Length ◽

Thick Filament ◽

Cycling Rate ◽

Cross Bridge ◽

Parallel Change ◽

Force Velocity ◽

Cross Bridges ◽

Trachealis Muscle

Force-velocity curves measured at different times during tetani of sheep trachealis muscle were analyzed to assess whether velocity slowing could be explained by thick-filament lengthening. Such lengthening increases force by placing more cross bridges in parallel on longer filaments and decreases velocity by reducing the number of filaments spanning muscle length. From 2 s after the onset of stimulation, when force had achieved 42% of it final value, to 28 s, when force had been at its tetanic plateau for ∼15 s, velocity decreases were exactly matched by force increases when force was adjusted for changes in activation, as assessed from the maximum power value in the force-velocity curves. A twofold change in velocity could be quantitatively explained by a series-to-parallel change in the filament lattice without any need to postulate a change in cross-bridge cycling rate.

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Agonist activation modulates cross-bridge states in single vascular smooth muscle cells

AJP Cell Physiology ◽

10.1152/ajpcell.1993.264.1.c103 ◽

1993 ◽

Vol 264 (1) ◽

pp. C103-C108 ◽

Cited By ~ 10

Author(s):

F. V. Brozovich ◽

M. Yamakawa

Keyword(s):

Smooth Muscle ◽

Steady State ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Vascular Smooth Muscle Cells ◽

Muscle Cells ◽

Relative Population ◽

Cross Bridge ◽

Cross Bridges ◽

State Force

To determine cross-bridge properties during agonist-stimulated contractions, steady-state force and relative steady-state stiffness were recorded at rest (pCa 9) and during both full (pCa 4) and partial (pCa 7) Ca2+ activations of isolated single alpha-toxin permeabilized vascular smooth muscle cells. For pCa 4 and pCa 7, agonist (1 microM histamine) activation resulted in significant (P < 0.05) increases in both force and stiffness. The agonist-induced increase of steady-state force was significantly (P < 0.05) greater than that of stiffness; at pCa 4, there was a 48% increase for force vs. 17% for stiffness, and, at pCa 7, there was a 160% increase for force vs. 57% for stiffness. The increase in force and stiffness after agonist prestimulation implies that the number of attached cross bridges has increased. However, after agonist prestimulation, we found that the increase of force was greater (P < 0.05) than that of stiffness, resulting in a greater force at any given level of stiffness. Thus these data indicate that agonist activation, presumably via activation of a G protein, increases the relative force per attached cross bridge, possibly by modulating the kinetics of the actomyosin adenosinetriphosphatase to increase in the relative population of cross bridges in force-producing states [actinomyosin (AM) or AM.ADP].

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

AJP Cell Physiology ◽

10.1152/ajpcell.1988.254.1.c99 ◽

1988 ◽

Vol 254 (1) ◽

pp. C99-C106 ◽

Cited By ~ 292

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.

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