Time dependence of shortening velocity in tracheal smooth muscle

1986 ◽  
Vol 251 (3) ◽  
pp. C435-C442 ◽  
Author(s):  
N. L. Stephens ◽  
M. L. Kagan ◽  
C. S. Packer
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Contraction ◽  
Tracheal Smooth Muscle ◽  
Shortening Velocity ◽  
Time Intervals ◽  
Activity Maximum ◽  
Cross Bridge ◽  
Cross Bridges ◽  
Latch State ◽  
Stimulation Of

It seems fairly well established that in the early phase of smooth muscle contraction cross bridges cycle at a relatively rapid rate. Later on these are replaced by very slowly cycling cross bridges or "latch bridges," operating with high economy. We describe a method to identify the time at which the transition occurs. By abruptly applying a light afterload at varying time intervals after stimulation of a canine tracheal smooth muscle, a point in time could be identified when cross-bridge cycling slowed. This was called the transition time. Because this transition was load dependent, the study was repeated with the preload abruptly reduced to zero. This permitted analysis of data in terms of cross-bridge activity. Maximum zero load velocity (Vo) of the contractile machinery was plotted against time and yielded a biphasic curve. The descending limb of the curve was fitted by a curve of the form Vo(t) = alpha e-K1t + beta e-K2t; K1 was almost three times greater than K2. We speculate that the faster rate constant represented activity of the early rapidly cycling cross bridges, and the slower constant reflected cycling rates in the latch state. These results are consistent with the latch bridge hypothesis put forward by Dillon et al. and enable us to provide a first approximation of the relative velocities of the two types of cross bridges.

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

1988 ◽  
Vol 255 (1) ◽  
pp. C86-C94 ◽  
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.

Myosin phosphorylation and regulation of cross-bridge cycle in tracheal smooth muscle

1983 ◽  
Vol 244 (3) ◽  
pp. C182-C187 ◽  
Author(s):  
W. T. Gerthoffer ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Tracheal Smooth Muscle ◽  
Shortening Velocity ◽  
Active Stress ◽  
Myosin Phosphorylation ◽  
Cross Bridge ◽  
Rapid Changes ◽  
Cross Bridges ◽  
Resting Muscle ◽  
Isotonic Shortening

We have tested the hypothesis that phosphorylation of the 20,000-dalton myosin light chains (LC 20) in rabbit tracheal smooth muscle modulates cross-bridge kinetics and isotonic shortening velocity. The thin muscle [190 +/- 10 (SE) microns] allowed detection of rapid changes in carbachol-induced active stress development, LC 20 phosphorylation, and isotonic shortening velocities. Phosphorylation of the LC 20 in resting muscle was 0.12 +/- 0.04 mol Pi/mol LC 20. Carbachol (10(-5) M) increased the level of phosphorylation to 0.46 +/- 0.03 mol Pi/mol LC 20 within 30 s. Phosphorylation then declined significantly as steady-state active stress was reached. A positive correlation was always found between LC 20 phosphorylation and shortening velocity. This result supports the hypothesis that the level of myosin phosphorylation was related to the mean cross-bridge cycling rate rather than the number of cross bridges contributing to the developed stress. Dephosphorylation of LC 20 occurred at about the same rate as the decline in shortening velocity and stress upon stimulus washout.

Cross-bridge regulation by Ca2+-dependent phosphorylation in amphibian smooth muscle

2001 ◽  
Vol 281 (6) ◽  
pp. R1769-R1777 ◽  
Author(s):  
C. J. Wingard ◽  
J. M. Nowocin ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Regulatory Mechanism ◽  
Smooth Muscle Contraction ◽  
Field Stimulation ◽  
Myosin Regulatory Light Chain ◽  
Rapid Rise ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Length Relationship ◽  
Cross Bridges

A covalent regulatory mechanism involving Ca2+-dependent cross-bridge phosphorylation determines both the number of cycling cross bridges and cycling kinetics in mammalian smooth muscle. Our objective was to determine whether a similar regulatory mechanism governed smooth muscle contraction from a poikilothermic amphibian in a test of the hypothesis that myosin regulatory light chain (MRLC) phosphorylation could modulate shortening velocity. We measured MRLC phosphorylation of Rana catesbiana urinary bladder strips at 25°C in tonic contractions in response to K+ depolarization, field stimulation, or carbachol stimulation. The force-length relationship was characterized by a steep ascending limb and a shallow descending limb. There was a rapid rise in unloaded shortening velocity early in a contraction, which then fell and was maintained at low rates while high force was maintained. In support of the hypothesis, we found a positive correlation of the level of myosin phosphorylation and an estimate of tissue shortening velocity. These results suggest that MRLC phosphorylation in amphibian smooth muscle modulates both the number of attached cross bridges (force) and the cross-bridge cycling kinetics (shortening velocity) as in mammalian smooth muscle.

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 The latch-bridge hypothesis of smooth muscle contraction

2005 ◽  
Vol 83 (10) ◽  
pp. 857-864 ◽  
Author(s):  
Richard A Murphy ◽  
Christopher M Rembold
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Striated Muscle ◽  
Smooth Muscle Contraction ◽  
Myosin Light Chain Phosphatase ◽  
Shortening Velocity ◽  
General Applicability ◽  
Cross Bridge ◽  
Mechanical Transduction

In contrast to striated muscle, both normalized force and shortening velocities are regulated functions of cross-bridge phosphorylation in smooth muscle. Physiologically this is manifested as relatively fast rates of contraction associated with transiently high levels of cross-bridge phosphorylation. In sustained contractions, Ca2+, cross-bridge phosphorylation, and ATP consumption rates fall, a phenomenon termed "latch". This review focuses on the Hai and Murphy (1988a) model that predicted the highly non-linear dependence of force on phosphorylation and a directly proportional dependence of shortening velocity on phosphorylation. This model hypothesized that (i) cross-bridge phosphorylation was obligatory for cross-bridge attachment, but also that (ii) dephosphorylation of an attached cross-bridge reduced its detachment rate. The resulting variety of cross-bridge cycles as predicted by the model could explain the observed dependencies of force and velocity on cross-bridge phosphorylation. New evidence supports modifications for more general applicability. First, myosin light chain phosphatase activity is regulated. Activation of myosin phosphatase is best demonstrated with inhibitory regulatory mechanisms acting via nitric oxide. The second modification of the model incorporates cooperativity in cross-bridge attachment to predict improved data on the dependence of force on phosphorylation. The molecular basis for cooperativity is unknown, but may involve thin filament proteins absent in striated muscle.Key words: chemo-mechanical transduction, activation-contraction coupling, cross-bridge, myosin light chain kinase, myosin light chain phosphatase, phosphorylation, cooperativity.

Relaxation of smooth muscle

1994 ◽  
Vol 72 (11) ◽  
pp. 1345-1350 ◽  
Author(s):  
N. L. Stephens ◽  
H. Jiang
Keyword(s):  
Smooth Muscle ◽  
Muscle Relaxation ◽  
Late Phase ◽  
Contractile Element ◽  
Smooth Muscle Relaxation ◽  
Shortening Velocity ◽  
Cycling Rate ◽  
Cross Bridge ◽  
Cross Bridges ◽  
And Control

We have demonstrated that in dogs antigen sensitization results in alterations of contractile properties. These changes could account for the hyperresponsiveness reported in asthma. The failure of the muscle to relax could be another important factor responsible for maintaining high airway resistance. We therefore developed an index of isotonic relaxation, t1/2,CE (half time for relaxation that is independent of muscle load and initial contractile element length), for evaluation of the relaxation process. Because the maximum shortening velocity at 2 s but not at 10 s was greater in sensitized bronchial smooth muscle than that in controls, studies of relaxation were also undertaken at these two times. The mean half-relaxation time indicated by t1/2,CE showed no difference between sensitized and control muscles after 10 s of stimulation (8.38 ± 0.92 vs. 7.78 ± 0.93 s, means ± SE); however, it was prolonged significantly in the sensitized muscle only stimulated for 1 s (12.74 ± 2.5 s, mean ± SE) compared with the control (6.98 ± 1.01 s). During the late phase of isotonic relaxation, both groups showed an unexpected spontaneous increase in zero-load shortening velocity, which is an index of cross-bridge cycling rate. We conclude that (i) both contraction and relaxation properties of early normally cycling cross bridges are altered after sensitization and these changes may account for the hyperresponsiveness observed in asthmatics and (ii) the cross-bridge cycling rate increases spontaneously during isotonic relaxation, probably as a result of reactivation of the contractile mechanism.Key words: smooth muscle relaxation, isotonic relaxation, spontaneous activation in late relaxation, mechanisms for airway hyperresponsiveness, new index of muscle relaxation.

An expanded latch-bridge model of protein kinase C-mediated smooth muscle contraction

2005 ◽  
Vol 98 (4) ◽  
pp. 1356-1365 ◽  
Author(s):  
Chi-Ming Hai ◽  
Hak Rim Kim
Keyword(s):  
Smooth Muscle ◽  
Atpase Activity ◽  
Thin Filament ◽  
Muscle Mechanics ◽  
Smooth Muscle Contraction ◽  
Myosin Phosphorylation ◽  
Cross Bridge ◽  
Bridge Model ◽  
Cross Bridges ◽  
Smooth Muscle Mechanics

A thin-filament-regulated latch-bridge model of smooth muscle contraction is proposed to integrate thin-filament-based inhibition of actomyosin ATPase activity with myosin phosphorylation in the regulation of smooth muscle mechanics. The model included two latch-bridge cycles, one of which was identical to the four-state model as proposed by Hai and Murphy ( Am J Physiol Cell Physiol 255: C86–C94, 1988), whereas the ultraslow cross-bridge cycle has lower cross-bridge cycling rates. The model-fitted phorbol ester induced slow contractions at constant myosin phosphorylation and predicted steeper dependence of force on myosin phosphorylation in phorbol ester-stimulated smooth muscle. By shifting cross bridges between the two latch-bridge cycles, the model predicts that a smooth muscle cell can either maintain force at extremely low-energy cost or change its contractile state rapidly, if necessary. Depending on the fraction of cross bridges engaged in the ultraslow latch-bridge cycle, the model predicted biphasic kinetics of smooth muscle mechanics and variable steady-state dependencies of force and shortening velocity on myosin phosphorylation. These results suggest that thin-filament-based regulatory proteins may function as tuners of actomyosin ATPase activity, thus allowing a smooth muscle cell to have two discrete cross-bridge cycles with different cross-bridge cycling rates.

Cross-bridge kinetics and shortening in smooth muscle

1994 ◽  
Vol 72 (11) ◽  
pp. 1334-1337 ◽  
Author(s):  
Per Hellstrand
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Isometric Force ◽  
Muscle Mechanics ◽  
Cross Bridge ◽  
Intracellular Ca ◽  
Cross Bridges ◽  
Latch State ◽  
Smooth Muscle Mechanics ◽  
Low Rate

Stiffness measurements were performed on smooth muscle preparations from guinea-pig taenia coli to obtain information on the number of attached cross bridges under varying contractile conditions. The normalized stiffness of the cross-bridge system in smooth muscle may be of a magnitude similar to that assumed in skeletal muscle. Transition from isometric contraction to unloaded shortening was associated with a decrease in stiffness to 50% or less of the isometric value, slightly higher than that found in skeletal muscle fibers. Comparison of phasic (5 s) and tonic (5 min) contractions showed lower Vmax, intracellular [Ca2+], and myosin 20 kDa light chain phosphorylation at 5 min, indicating development of a latch state. Isometric force and stiffness were identical in the two types of contraction. However, stiffness during unloaded shortening was greater in the latch state, which may be the result of the presence of a population of cross bridges with a low rate constant for detachment.Key words: smooth muscle mechanics, cross bridges, latch, myosin phosphorylation.

Physiological antagonism caused by adrenergic stimulation of canine tracheal muscle

1986 ◽  
Vol 60 (1) ◽  
pp. 216-224 ◽  
Author(s):  
A. R. Leff ◽  
J. Tallet ◽  
N. M. Munoz ◽  
N. Shoulberg
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Contraction ◽  
Tracheal Smooth Muscle ◽  
Adrenergic Blockade ◽  
Adrenergic Stimulation ◽  
Beta Adrenergic ◽  
Beta Adrenoceptor ◽  
Response Characteristics ◽  
Stimulation Of

We studied the simultaneous alpha- and beta-adrenergic response characteristics of canine tracheal smooth muscle in 398 strips from 67 dogs in vitro. Experiments were performed to determine the effects of beta-adrenergic blockade on the expression of the alpha-adrenoceptor contractile responses elicited by norepinephrine (NE), phenylephrine (PE), and clonidine (CLO). Maximal active tension caused by NE increased from 39.1 +/- 27.0 to 241 +/- 75.0 g/cm2 as the concentration of propranolol (PROP) was increased from 10(-6) to 10(-4) M. Augmentation of tracheal smooth muscle contraction caused by PE and CLO was also observed with progressive beta-adrenoceptor blockade; contraction to NE, PE, and CLO was blocked selectively with 3 X 10(-5) M phentolamine (PA) and phenoxybenzamine (PBZ). The beta-adrenergic relaxing properties of the same three agonists were also studied. After alpha-adrenergic blockade with PA or PBZ, all three agonists caused relaxation (NE greater than CLO greater than PE) of methacholine-induced contraction of tracheal smooth muscle that was reversed selectively with PROP. We demonstrate that NE, PE, and CLO cause simultaneous stimulation of both the alpha- and beta-adrenergic receptors in tracheal smooth muscle; the net response elicited is the result of adrenergic physiological antagonism and depends on the relative degree of alpha- and/or beta-adrenoceptor blockade.

Role of myosin light-chain phosphorylation in guinea pig gallbladder smooth muscle contraction

1994 ◽  
Vol 266 (3) ◽  
pp. G469-G474 ◽  
Author(s):  
R. J. Washabau ◽  
M. B. Wang ◽  
C. Dorst ◽  
J. P. Ryan
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Smooth Muscle Contraction ◽  
Myosin Light Chain Phosphorylation ◽  
Shortening Velocity ◽  
Cross Bridges ◽  
Isotonic Shortening

In acetylcholine (ACh)-stimulated gallbladder smooth muscle, we have previously shown that phosphorylation of the 20,000-Da myosin light chains is necessary for the initiation of contraction, that myosin is stably phosphorylated at steady state, and that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates during the period of steady-state isometric stress. The present studies were undertaken to determine whether 1) K+ (60 or 80 mM) or cholecystokinin (CCK, 10(-8) M) stimulation is accompanied by changes in myosin light-chain phosphorylation in gallbladder smooth muscle and 2) dephosphorylated noncycling cross bridges exist in K(+)- or CCK-stimulated gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light-chain phosphorylation were determined during contraction with K+ or CCK. Steady-state isometric stress was reached within 2.5 min of stimulation with K+ or CCK and was maintained for the duration of the stimulation. Stimulation with K+ or CCK was associated with rapid increases in myosin light-chain phosphorylation and maintenance of myosin light-chain phosphorylation during the stimulation. In contrast, isotonic shortening velocity was maximal at 1 min of stimulation with either K+ or CCK and then declined significantly to values that were only 26-32% of the peak velocity. These data, along with data from previous experiments with ACh, suggest that myosin light-chain phosphorylation is essential in the initiation of contraction in gallbladder smooth muscle, regardless of the source of Ca2+ or of the contractile agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

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