Myosin phosphorylation and contraction of feline esophageal smooth muscle

1985 ◽  
Vol 249 (1) ◽  
pp. C9-C14 ◽  
Author(s):  
N. W. Weisbrodt ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Mechanical Activation ◽  
Smooth Muscles ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Muscle Layer ◽  
Field Stimulation ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Isotonic Shortening

We tested the hypothesis that phosphorylation of the 20,000-Da light chain of myosin (LC 20) is related to mechanical activation of esophageal smooth muscle. Circular muscle layer strips of cat esophagus were taken from the lower esophageal sphincter (LES) and the distal esophageal body (EB). The LES strips developed tone spontaneously, and the EB strips were tonically contracted with carbachol. Both tissues relaxed in response to electrical-field stimulation. Phosphorylation of the LC 20 was determined in tissues quick-frozen during relaxation and during stress redevelopment after cessation of field stimulation. Stress and phosphorylation levels were low after 30 s of field stimulation, and a rapid contraction followed field stimulation. Phosphorylation in the LES increased from 0.043 +/- 0.029 to 0.328 +/- 0.043 mol Pi/mol LC 20 within 10 s after stimulation of the inhibitory nerves was terminated, while stress was still rising rapidly. Phosphorylation in the LES then declined to a steady-state value of 0.162 +/- 0.034 mol Pi/mol LC 20 after 10 min. Isotonic shortening velocities at a constant afterload following a quick release showed changes with time that were proportional to the level of phosphorylation. This was also true for values of maximal shortening velocity estimated for zero external load and for the rate of stress redevelopment after a step shortening. Comparable measurements were made in the carbachol-contracted EB. These results indicate that visceral smooth muscles, which normally function tonically (LES) or phasically (EB), exhibit an initial rapid mechanical activation associated with myosin phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the properties of canine colonic smooth muscle in culture

1993 ◽  
Vol 265 (5) ◽  
pp. C1433-C1442 ◽  
Author(s):  
M. J. Rogers ◽  
S. M. Ward ◽  
M. A. Horner ◽  
K. M. Sanders ◽  
B. Horowitz
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscles ◽  
Potential Gradient ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Muscle Layer ◽  
Enteric Neurons ◽  
Resting Potential ◽  
Northern Analysis ◽  
Functional Components

We have developed and characterized an organ culture system that maintains the viability of colonic smooth muscles. Morphological, mechanical, electrical, and molecular properties of cultured canine colonic circular muscles were determined. Strips of circular muscle were cultured for up to 6 days. The smooth muscle phenotype was retained during culture; muscles contracted to agonists and responded to electrical field stimulation, suggesting that intrinsic nerves also survived in culture. Morphological analysis showed identifiable smooth muscle cells, enteric neurons, and interstitial cells, but some alterations in ultrastructure were also observed. Mechanical responses to acetylcholine suggested that the muscles developed supersensitivity during the culture period. The resting membrane potentials of cells near the submucosal surface of the circular muscle layer decreased from -82 mV on day 0 to -55 mV on day 3. Similar changes in the resting potential gradient occur when colonic muscles are treated with inhibitors of the Na(+)-K(+)-ATPase. Resting potentials of day 3 muscles remained constant in low external K+ (0.1 mM), suggesting little contribution of the pump to resting potential. Northern analysis of RNA from muscles cultured up to 6 days showed that the alpha 2-isoform of the pump decreased. The data suggest that organ-cultured strips of smooth muscle may provide a useful tool for evaluating electrical and mechanical events in conjunction with molecular analysis of functional components.

Excitatory and inhibitory responses of Oddi's sphincter in guinea pigs

1991 ◽  
Vol 260 (4) ◽  
pp. G615-G624 ◽  
Author(s):  
T. Hirose ◽  
Y. Ito
Keyword(s):  
Smooth Muscle ◽  
Action Potentials ◽  
Regional Differences ◽  
Longitudinal Muscle ◽  
Smooth Muscles ◽  
Central Area ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Muscle Cells ◽  
Field Stimulation

We examined the intrinsic motor innervation of the guinea pig choledochoduodenal junction and actions of cholecystokinin octapeptide (CCK-OP) on contractile and membrane activity of circular and longitudinal smooth muscles from three different areas: close to the choledochal sphincter (I); central area in the ampulla (II); and close to the duodenal papilla (III). In response to electrical field stimulation, circular muscle strips showed an initial twitchlike contraction followed by relaxation in areas I and II and only a transient relaxation in the muscle strips prepared from area III. In the longitudinal strips, the regional differences in response to the field stimulation were not prominent, and biphasic twitchlike contractions were observed in areas I, II, and III. Electric field stimulation evoked excitatory junction potentials (EJPs), inhibitory junction potentials (IJPs), or biphasic membrane response (initial EJP followed by an IJP) in the circular and longitudinal smooth muscle cells. Prominent regional differences were observed in areas I, II, and III. Namely, in area III both the circular and longitudinal muscle layers IJPs predominated, whereas in area I the response was predominantly excitatory. CCK-OP (greater than 10-8M) evoked repetitive action potentials in the circular muscle cells, and CCK-OP increased the frequency of slow waves or the spontaneous action potentials in longitudinal muscle cells. CCK-OP enhanced the amplitude of the IJPs and EJPs in both muscle layers. It would thus appear that bile flow is controlled by complex combinations of contraction and relaxation of the smooth muscle that may be due to regional differences in excitatory and inhibitory innervations.

Origin of Motion in the Human Ureter: Mechanics, Energetics and Kinetics of the Myosin Molecular Motors

2012 ◽  
Vol 79 (2) ◽  
pp. 123-129 ◽  
Author(s):  
Romina Vargiu ◽  
Anna Perinu ◽  
Antonello De Lisa ◽  
Frank Tintrup ◽  
Francesco Manca ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Molecular Motors ◽  
Circular Muscle ◽  
Muscle Layer ◽  
Shortening Velocity ◽  
Smooth Muscle Layer ◽  
Circular Smooth Muscle ◽  
Longitudinal Smooth Muscle ◽  
Human Ureter

Background Ureteral peristalsis is the result of coordinated mechanical motor performance of longitudinal and circular smooth muscle layer of the ureter wall. The main aim of this study was to characterize in smooth muscle of proximal segments of human ureter, the mechanical properties at level of muscle tissue and at level of myosin molecular motors. Methods Ureteral samples were collected from 15 patients, who underwent nephrectomy for renal cancer. Smooth muscle strips longitudinally and circularly oriented from proximal segments of human ureter were used for the in vitro experiments. Mechanical indices including the maximum unloaded shortening velocity (Vmax), and the maximum isometric tension (P0) normalized per cross-sectional area, were determined in vitro determined in electrically evoked contractions of longitudinal and circular smooth muscle strips. Myosin cross-bridge (CB) number per mm2 (Ψ) the elementary force per single CB (Ψ) and kinetic parameters were calculated in muscle strips, using Huxley's equations adapted to nonsarcomeric muscles. Results Longitudinal smooth muscle strips exhibited a significantly (p<0.05) faster Vmax (63%) and a higher P0 (40%), if compared to circular strips. Moreover, longitudinal muscle strips showed a significantly higher unitary force (Ψ) per CB. However, no significant differences were observed in CB number, the attachment (f1) and the detachment (g2) rate constants between longitudinal and circular muscle strips. Conclusions The main result obtained in the present work documents that the mechanical, energetic and unitary forces per CB of longitudinal layer of proximal ureter are better compared to the circular one; these preliminary findings suggested, unlike intestinal smooth muscle, a major role of longitudinal smooth muscle layer in the ureter peristalsis.

Cross-bridge dephosphorylation and relaxation of vascular smooth muscle

1989 ◽  
Vol 256 (2) ◽  
pp. C282-C287 ◽  
Author(s):  
C. M. Hai ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Time Course ◽  
Electrical Field Stimulation ◽  
Shortening Velocity ◽  
Electrical Field ◽  
Cross Bridge ◽  
Time Course Data ◽  
Necessary And Sufficient ◽  
Isotonic Shortening

We tested the hypothesis that relaxation in vascular smooth muscle is the result of inactivation of myosin light chain kinase and cross-bridge dephosphorylation. Fast neurally mediated contractions of swine carotid medial strips were induced by electrical field stimulation. Termination of the stimulus resulted in relaxation with a half time of 2 min. Nifedipine (0.1 microM) increased the relaxation rate without significant effects on the contractile response. Cross-bridge dephosphorylation was much faster than stress decay with basal levels reached within 1 min when 73% of the developed stress remained. The time-course data of dephosphorylation and stress were analyzed with a model that predicted the dependences of stress and isotonic shortening velocity on cross-bridge phosphorylation during contraction. Rate constants resolved from contraction data also fitted the relaxation data when the model's prediction was corrected for estimated errors in the phosphorylation measurements. Because Ca2+-dependent cross-bridge phosphorylation was the only postulated regulatory mechanism in the model, these results are consistent with the hypothesis that cross-bridge dephosphorylation is necessary and sufficient to explain relaxation in the swine carotid media.

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.

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.

Contraction history modulates isotonic shortening velocity in smooth muscle

1993 ◽  
Vol 265 (2) ◽  
pp. C467-C476 ◽  
Author(s):  
S. J. Gunst ◽  
M. F. Wu ◽  
D. D. Smith
Keyword(s):  
Smooth Muscle ◽  
Muscle Length ◽  
Electrical Field Stimulation ◽  
Contractile Element ◽  
Shortening Velocity ◽  
Linear Rate ◽  
Velocity Relationship ◽  
Force Velocity ◽  
Contractile Activation ◽  
Isotonic Shortening

The effect of contraction history on the isotonic shortening velocity of canine tracheal smooth muscle was investigated. Muscles were contracted isometrically for 20 s at initial lengths of L(o) (length of maximal active force), 85% L(o), or 70% L(o) using electrical field stimulation. Muscles were then allowed to shorten isotonically under different afterloads either with or without first being subjected to a step decrease in length to 70% L(o). Instantaneous velocities were plotted against instantaneous muscle length during isotonic shortening. Regardless of protocol, the velocity at any muscle length during shortening was lower when the muscle was initially activated at a longer length. The isotonic shortening velocity decreased progressively during shortening at a nearly linear rate with respect to instantaneous muscle length under all conditions. Results suggest that a longer muscle length at the time of activation leads to the development of higher loads on the contractile element during subsequent shortening, resulting in a slower shortening velocity. This plasticity of the force-velocity relationship may result from cytostructural reorganization of the smooth muscle cells in response to contractile activation at different muscle lengths.

Stimulus-response relationships for isotonic shortening and isometric tension generation in rabbit trachealis

1994 ◽  
Vol 77 (4) ◽  
pp. 1638-1643 ◽  
Author(s):  
A. Opazo-Saez ◽  
P. D. Pare
Keyword(s):  
Smooth Muscle ◽  
Isometric Force ◽  
Electrical Field Stimulation ◽  
Isometric Tension ◽  
Maximal Response ◽  
Field Stimulation ◽  
Electrical Field ◽  
Increased Sensitivity ◽  
Isotonic Shortening

Nonspecific bronchial hyperresponsiveness in asthma is characterized by increased maximal airway narrowing (reactivity) and increased sensitivity of the airways. A decreased load on airway smooth muscle (ASM) has been suggested as a mechanism of increased reactivity. We hypothesized that decreased ASM load can also cause a leftward shift in the dose-response curve and explain increased sensitivity. We tested this hypothesis using rabbit tracheal smooth muscle strips in vitro by measuring isotonic shortening and isometric force during electrical field stimulation (1–100 Hz) at the length at which maximal active tension developed (Lmax), 90% Lmax, and 110% Lmax The frequency-response relationships expressed as frequency vs. percent maximal shortening or tension were not different at Lmax or 110% Lmax, but at 90% Lmax the frequency vs. shortening relationship was significantly shifted leftward relative to the frequency vs. tension relationship (P < 0.05). The electrical field stimulation frequencies that produced 50% maximal response for isometric tension and for isotonic shortening, respectively, were 6.7 +/- 1.9 and 3.9 +/- 0.7 Hz at 90% Lmax, 9.2 +/- 2.1 and 7.5 +/- 1.9 Hz at 100% Lmax, and 2.8 +/- 1.0 and 1.2 +/- 0.5 Hz at 110% Lmax. We conclude that, at lengths below Lmax, isotonic shortening is facilitated compared with isometric tension and therefore decreased ASM load in vivo may result in increased sensitivity.

Nitric oxide as a mediator of nonadrenergic noncholinergic neurotransmission

1992 ◽  
Vol 262 (3) ◽  
pp. G379-G392 ◽  
Author(s):  
K. M. Sanders ◽  
S. M. Ward
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Nerve Stimulation ◽  
Smooth Muscles ◽  
Extracellular Fluid ◽  
Electrical Field Stimulation ◽  
Enteric Neurons ◽  
Field Stimulation ◽  
Gi Tract

Part of the regulation of gastrointestinal (GI) smooth muscles is provided by nonadrenergic noncholinergic (NANC) nerves. Stimulation of these nerves, either by field stimulation or via neural reflex pathways, elicits hyperpolarization of postjunctional smooth muscle membranes referred to as inhibitory junction potentials and relaxation. The transmitter(s) that mediate NANC inhibitory neural transmission have been a controversial topic for nearly 30 years. Recent evidence suggests that nitric oxide (NO) may serve as a NANC inhibitory transmitter in the GI tract. This hypothesis is supported by the following. 1) Immunohistochemical studies have shown that the enzyme necessary for NO synthesis is expressed in enteric neurons. In vitro studies of muscles from nearly all levels of GI tract have also shown that arginine analogues, which inhibit NO synthesis, reduce inhibitory effects of NANC neurotransmission. Effects of arginine analogues can be restored by addition of excess L-arginine, the substrate for NO synthesis. These data suggest that NO can be synthesized by enteric nerves. 2) Bioassays have demonstrated nerve-evoked release of a substance that has been identified as NO during NANC nerve stimulation. Oxyhemoglobin, known to bind to and sequester NO, also blocks NANC responses. These data suggest that NO is released into extracellular fluid during nerve stimulation. 3) Addition of NO causes rapid hyperpolarization of GI smooth muscle cells and relaxes muscles strips. These effects are similar to NANC nerve responses. NO and electrical field stimulation also increase tissue guanosine 3',5'-cyclic monophosphate, which may be the second messenger involved in NANC responses. 4) Removal of NO is easily accomplished by its rapid spontaneous breakdown in physiological solutions. 5) The pharmacology of NO and the NANC neurotransmitter in many preparations is similar, e.g., oxyhemoglobin blocks responses to NANC nerve stimulation and to exogenous NO. In summary, it would appear that many of the criteria necessary for NO to be considered a neurotransmitter have been satisfied.

scholarly journals Dissociation between hysteresivity and tension in constricted tracheal and parenchymal strips

1998 ◽  
Vol 85 (1) ◽  
pp. 91-97 ◽  
Author(s):  
Francesco G. Salerno ◽  
Mara S. Ludwig
Keyword(s):  
Smooth Muscle ◽  
Electrical Field Stimulation ◽  
Lung Parenchyma ◽  
Hysteretic Behavior ◽  
Contractile Element ◽  
Organ Bath ◽  
Field Stimulation ◽  
Shortening Velocity ◽  
Electrical Field ◽  
Contractile State

The object of this study was to investigate how changes in the contractile state of smooth muscle would modify oscillatory mechanics of tracheal muscle and lung parenchyma during agonist challenge. Guinea pig tracheal and parenchymal lung strips were suspended in an organ bath. Measurements of length ( L) and tension (T) were recorded during sinusoidal oscillations under baseline conditions and after challenge with 1 mM ACh. Measurements were also obtained in strips pretreated with the calmodulin inhibitor calmidazolium (Cmz) or staurosporine (Stauro), a protein kinase C inhibitor. Elastance (E) and resistance (R) were calculated by fitting changes in T, L, and Δ L/Δ tto the equation of motion. Hysteresivity (η) was obtained from the following equation: η = (R/E)2π f, where f is frequency. Finally, maximal unloaded shortening velocity during electrical field stimulation was measured in Cmz-pretreated and control tracheal strips. In tracheal strips, pretreatment with Cmz caused a significant decrease in the η response to ACh challenge and in maximal unloaded shortening velocity measured during electrical field stimulation; Stauro decreased the T, E, and R response to ACh. In parenchymal strips, Cmz decreased the η response, whereas Stauro had no effect. These results suggest that modifications in the contractile state of the smooth muscle are reflected in changes in the hysteretic behavior and that T and η may be controlled independently. Second, inasmuch as changes in η were similar in parenchymal and tracheal strips, the contractile element is implicated as the structure responsible for constriction-induced changes in the mechanical behavior of the lung periphery.

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