The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Richard L Lieber - One of the best experts on this subject based on the ideXlab platform.
-
psoas muscle architectural design in vivo sarcomere length range and passive tensile properties support its role as a lumbar spine stabilizer
Spine, 2011Co-Authors: Gilad J Regev, Richard L Lieber, Choll W Kim, Akihito Tomiya, Yu Po Lee, Hossein Ardeschir Ghofrani, Steven R Garfin, Samuel R WardAbstract:STUDY DESIGN Controlled laboratory and cross-sectional study designs. OBJECTIVE To determine psoas major (PM) muscle architectural properties, in vivo sarcomere-length operating range, and passive mechanical properties. SUMMARY OF BACKGROUND DATA PM is an important hip flexor but its role in lumbar spine function is not fully understood. Several investigators have detailed the gross anatomy of PM, but comprehensive architectural data and in vivo Length-Tension and passive mechanical behaviors have not been documented. METHODS PM was isolated in 13 cadaver specimens, permitting architectural measurements of physiological cross-sectional area (PCSA), normalized fiber length (Lf), and Lf:muscle length (Lm) ratio. Sarcomere lengths were measured in vivo from intraoperative biopsies taken with the hip joint in flexed and extended positions. Single-fiber and fiber bundle tensile properties and titin molecular weight were then measured from separate biopsies. RESULTS Architecturally, average PCSA was 18.45 ± 1.32 cm2, average Lf was 12.70 ± 2 cm, and average Lf: Lm was 0.48 ± 0.06. Intraoperative sarcomere length measurements revealed that the muscle operates from 3.18 ± 0.20 μm with hip flexed at 10.7° ± 13.9° to 3.03 ± 0.22 μm with hip flexed at 55.9° ± 21.4°. Passive mechanical data demonstrated that the elastic modulus of the PM muscle fibers was 37.44 ± 9.11 kPa and of fiber bundles was 55.3 ± 11.8 kPa. CONCLUSION Analysis of PM architecture demonstrates that its average Lf and passive biomechanical properties resemble those of the lumbar erector spinae muscles. In addition, PM sarcomere lengths were confined to the descending portion of the Length-Tension Curve allowing the muscle to become stronger as the hip is flexed and the spine assumes a forward leaning posture. These findings suggest that the human PM has architectural and physiologic features that support its role as both a flexor of the hip and a dynamic stabilizer of the lumbar spine.
-
the external anal sphincter operates at short sarcomere length in humans
Neurogastroenterology and Motility, 2011Co-Authors: Ravinder K Mittal, Richard L Lieber, Geoff Sheean, Bikram S Padda, Raj M RajasekaranAbstract:Background The length at which a muscle/sarcomere operates in vivo (operational length) and the length at which it generates maximal stress (optimal length) can be quite different. In a previous study, we found that the rabbit external anal sphincter (EAS) operates on the ascending limb of the length–tension Curve, in other words at lengths shorter than its optimal length (short sarcomere length). In this study, we tested whether the human EAS muscle also operates at a short sarcomere length. Methods The length–tension relationship of the EAS muscle was studied in vivo in 10 healthy nullipara women. EAS muscle length was altered by anal distension using custom-designed probes of 5, 10, 15, and 20 mm diameter. Probes were equipped with a sleeve sensor to measure anal canal pressure. The EAS muscle electromyograph (EMG) was recorded using wire electrodes. Ultrasound images of anal canal were obtained to measure EAS muscle thickness and anal canal diameter. EAS muscle stress was calculated from the anal canal pressure, inner radius, and thickness of the EAS muscle. Key Results Rest and squeeze stress of the anal canal increased with the increase in probe size. Similarly, the change in anal canal stress, i.e. the difference between the rest and the squeeze, which represents the active contribution of EAS to the anal canal stress, increased with the increase in probe size. However, increase in probe size was not associated with an increase in the external anal sphincter EMG activity. Conclusions & Inferences Increase in EAS muscle stress with the increase in probe size, in the presence of constant EMG (neural input), demonstrates that the human EAS muscle operates on the ascending limb of the length–tension Curve or at low sarcomere lengths. We propose that surgically adjusting EAS sarcomere length may represent a novel strategy to treat fecal incontinence in humans.
-
correlation between isometric force and intramuscular pressure in rabbit tibialis anterior muscle with an intact anterior compartment
Muscle & Nerve, 2009Co-Authors: Taylor M Winters, Richard L Lieber, Kenton R Kaufman, Genaro S Sepulveda, Patrick S Cottler, Samuel R WardAbstract:To determine the degree to which intramuscular pressure (IMP) and muscle force are correlated in an intact compartment, a custom pressure transducer was inserted into the rabbit tibialis anterior (TA) while activating the muscle via the peroneal nerve and measuring TA muscle force distal to the ankle retinaculum. In general, IMP was more variable compared to muscle force throughout the entire isometric Length-Tension relationship. In contrast to results obtained on isolated TA muscles, IMP-force relations with the compartment intact were not significantly different between the ascending and descending limbs of the Length-Tension Curve. Specifically, average relative pressure-force coefficients of determination (r2) were 0.76±0.11 for the active ascending limb and 0.98±0.01 for the active descending limb. These data demonstrate that muscle force and IMP are fairly well correlated under isometric conditions and that this relationship is not improved by measuring IMP in an intact environment.
-
architectural analysis and intraoperative measurements demonstrate the unique design of the multifidus muscle for lumbar spine stability
Journal of Bone and Joint Surgery American Volume, 2009Co-Authors: Samuel R Ward, Akihito Tomiya, Steven R Garfin, Lionel Gottschalk, Richard L LieberAbstract:Background: Muscular instability is an important risk factor for lumbar spine injury and chronic low-back pain. Although the lumbar multifidus muscle is considered an important paraspinal muscle, its design features are not completely understood. The purpose of the present study was to determine the architectural properties, in vivo sarcomere length operating range, and passive mechanical properties of the human multifidus muscle. We hypothesized that its architecture would be characterized by short fibers and a large physiological cross-sectional area and that it would operate over a relatively wide range of sarcomere lengths but would have very stiff passive material properties. Methods: The lumbar spines of eight cadaver specimens were excised en bloc from T12 to the sacrum. Multifidus muscles were isolated from each vertebral level, permitting the architectural measurements of mass, sarcomere length, normalized fiber length, physiological cross-sectional area, and fiber length-to-muscle length ratio. To determine the sarcomere length operating range of the muscle, sarcomere lengths were measured from intraoperative biopsy specimens that were obtained with the spine in the flexed and extended positions. The material properties of single muscle fibers were obtained from passive stress-strain tests of excised biopsy specimens. Results: The average muscle mass (and standard error) was 146 ± 8.7 g, and the average sarcomere length was 2.27 ± 0.06 μm, yielding an average normalized fiber length of 5.66 ± 0.65 cm, an average physiological cross-sectional area of 23.9 ± 3.0 cm2, and an average fiber length-to-muscle length ratio of 0.21 ± 0.03. Intraoperative sarcomere length measurements revealed that the muscle operates from 1.98 ± 0.15 μm in extension to 2.70 ± 0.11 μm in flexion. Passive mechanical data suggested that the material properties of the muscle are comparable with those of muscles of the arm or leg. Conclusions: The architectural design (a high cross-sectional area and a low fiber length-to-muscle length ratio) demonstrates that the multifidus muscle is uniquely designed as a stabilizer to produce large forces. Furthermore, multifidus sarcomeres are positioned on the ascending portion of the Length-Tension Curve, allowing the muscle to become stronger as the spine assumes a forward-leaning posture. Clinical Relevance: These findings demonstrate that the human multifidus muscle is designed to function as a dynamic stabilizer of the lumbar spine.
-
correlation between active and passive isometric force and intramuscular pressure in the isolated rabbit tibialis anterior muscle
Journal of Biomechanics, 2003Co-Authors: Jennifer Davis, Kenton R Kaufman, Richard L LieberAbstract:The purpose of this study was to quantify the relationship between intramuscular pressure (IMP) and muscle force during isometric muscle contraction of the rabbit tibialis anterior (TA) absent the effect of either bone or fascia. To quantify this relationship, length–tension experiments were performed on the isolated TA of the New Zealand White rabbit (mass=2.570.5 kg, n ¼ 12). The knee was fixed in a custom jig, the distal tendon of the TA was attached to a servomotor, and a 360mm fiber optic pressure transducer was inserted into the TA. The peroneal nerve was stimulated to define optimal length (L0). The length–tension Curve was created using 40 Hz isometric contractions with 2-min rest intervals between each contraction. Measurements began at L0 � 50%Lf and progressed to L0 þ 50%Lf ; changing the length–tension in 5% Lf increments after each contraction. Qualitatively, the length–tension Curve for isometric contractions was mimicked by the length–pressure Curve for both active and passive conditions. Linear regression was performed individually for each animal for the ascending and descending limb of the length– tension Curve and for active and passive conditions. Pressure–force coefficients of determination ranged from 0.138–0.963 for the active ascending limb and 0.343–0.947 for the active descending limb. Passive pressure coefficients of determination ranged from 0.045–0.842 for the ascending limb and 0.672–0.982 for the descending limb. These data indicate that IMP measurement provide a fairly accurate index of relative muscle force, especially at muscle lengths longer than optimal. r 2003 Elsevier Science Ltd. All rights reserved.
Uwe Proske - One of the best experts on this subject based on the ideXlab platform.
-
Rises in whole muscle passive tension of mammalian muscle after eccentric contractions at different lengths.
Journal of applied physiology (Bethesda Md. : 1985), 2003Co-Authors: Nicholas P Whitehead, David L Morgan, John E Gregory, Uwe ProskeAbstract:This is a report of experiments carried out on the medial gastrocnemius muscle of the anesthetized cat, investigating the effects of eccentric contractions carried out at different muscle lengths on the passive and active Length-Tension relationships. In one series of experiments, the motor supply to the muscle was divided into three approximately equal parts; in the other, whole muscles were used. Fifty eccentric contractions were carried out over different regions of the active Length-Tension Curve for each partial or whole muscle. Active and passive Length-Tension Curves were measured before and after the eccentric contractions. When eccentric contractions were carried out at longer lengths, there was a larger shift of the optimum length for active tension in the direction of longer muscle lengths and a larger fall in peak isometric tension. Passive tension was higher immediately after the eccentric contractions, and if the muscle was left undisturbed for 40 min, it increased further to higher values, particularly after contractions at longer lengths. A series of 20 passive stretches of the same speed and amplitude and covering the same length range as the active stretches, reduced the passive tension which redeveloped over a subsequent 40-min period. It is hypothesized that there are two factors influencing the level of passive tension in a muscle after a series of eccentric contractions. One is injury contractures in damaged muscle fibers tending to raise passive tension; the other is the presence of disrupted sarcomeres in series with still-functioning sarcomeres tending to reduce it.
-
The role of the Length-Tension Curve in the control of movement.
Advances in experimental medicine and biology, 2002Co-Authors: David L Morgan, Camilla Brockett, John E Gregory, Uwe ProskeAbstract:The Length-Tension Curve of muscle is one of the important descriptors of mechanical performance, and also a direct reflection of the underlying structure, particularly the number of sarcomeres connected in series in muscle fibres. This number is one of the most plastic properties of muscle, changing within days after changes in activity patterns. We propose that this adaptation is to prevent eccentric contractions from occurring beyond the optimum length for tension generation, since this is the region of sarcomere instability arid muscle damage. Evidence for this is presented for muscles from rats trained on a treadmill, and from motor units of the gastrocnemius muscle of the cat.
-
tension changes in the cat soleus muscle following slow stretch or shortening of the contracting muscle
The Journal of Physiology, 2000Co-Authors: D. L. Morgan, Nicholas P Whitehead, Andrew K Wise, J E Gregory, Uwe ProskeAbstract:The permanent extra tension after a stretch and the deficit of tension after a shortening in the soleus muscle of the anaesthetised cat were measured using distributed nerve stimulation across five channels. At low rates of stimulation the optimum length for a contraction was several millimetres longer than that when higher rates of stimulation were used, so that movements applied over the same length range could be on the descending limb of the full activation Curve but on the ascending limb of the submaximal activation Curve. The extra tension after stretch and the depression after shortening were present only near the peak and on the descending limb of the Length-Tension Curve. Effects on final tension of changing the speed and amplitude of stretches or shortenings were found to be small. Statistical analysis showed that variations in the tension excess or deficit due to changing stimulus rate could be entirely attributed to the effect of stimulus rate on the Length-Tension relation, as when length was expressed relative to optimum for each rate, stimulus rate was no longer a significant determinant of the tension excess or deficit. The extra tension after stretch and the depression after shortening disappeared if stimulation was interrupted and tension briefly fell to zero. These effects were explained in terms of a non-uniform distribution of sarcomere length changes at long muscle lengths. During stretch some sarcomeres are stretched to beyond overlap while others lengthen hardly at all. During shortening some sarcomeres shorten much further than others. These mechanisms have important implications for exercise physiology and sports medicine.
Samuel R Ward - One of the best experts on this subject based on the ideXlab platform.
-
psoas muscle architectural design in vivo sarcomere length range and passive tensile properties support its role as a lumbar spine stabilizer
Spine, 2011Co-Authors: Gilad J Regev, Richard L Lieber, Choll W Kim, Akihito Tomiya, Yu Po Lee, Hossein Ardeschir Ghofrani, Steven R Garfin, Samuel R WardAbstract:STUDY DESIGN Controlled laboratory and cross-sectional study designs. OBJECTIVE To determine psoas major (PM) muscle architectural properties, in vivo sarcomere-length operating range, and passive mechanical properties. SUMMARY OF BACKGROUND DATA PM is an important hip flexor but its role in lumbar spine function is not fully understood. Several investigators have detailed the gross anatomy of PM, but comprehensive architectural data and in vivo Length-Tension and passive mechanical behaviors have not been documented. METHODS PM was isolated in 13 cadaver specimens, permitting architectural measurements of physiological cross-sectional area (PCSA), normalized fiber length (Lf), and Lf:muscle length (Lm) ratio. Sarcomere lengths were measured in vivo from intraoperative biopsies taken with the hip joint in flexed and extended positions. Single-fiber and fiber bundle tensile properties and titin molecular weight were then measured from separate biopsies. RESULTS Architecturally, average PCSA was 18.45 ± 1.32 cm2, average Lf was 12.70 ± 2 cm, and average Lf: Lm was 0.48 ± 0.06. Intraoperative sarcomere length measurements revealed that the muscle operates from 3.18 ± 0.20 μm with hip flexed at 10.7° ± 13.9° to 3.03 ± 0.22 μm with hip flexed at 55.9° ± 21.4°. Passive mechanical data demonstrated that the elastic modulus of the PM muscle fibers was 37.44 ± 9.11 kPa and of fiber bundles was 55.3 ± 11.8 kPa. CONCLUSION Analysis of PM architecture demonstrates that its average Lf and passive biomechanical properties resemble those of the lumbar erector spinae muscles. In addition, PM sarcomere lengths were confined to the descending portion of the Length-Tension Curve allowing the muscle to become stronger as the hip is flexed and the spine assumes a forward leaning posture. These findings suggest that the human PM has architectural and physiologic features that support its role as both a flexor of the hip and a dynamic stabilizer of the lumbar spine.
-
the morphology of the masticatory apparatus facilitates muscle force production at wide jaw gapes in tree gouging common marmosets callithrix jacchus
The Journal of Experimental Biology, 2009Co-Authors: Carolyn M Eng, Samuel R Ward, Christopher J Vinyard, Andrea B TaylorAbstract:Common marmosets ( Callithrix jacchus ) generate wide jaw gapes when gouging trees with their anterior teeth to elicit tree exudate flow. Closely related cotton-top tamarins ( Saguinus oedipus ) do not gouge trees but share similar diets including exudates. Maximizing jaw opening theoretically compromises the bite forces that marmosets can generate during gouging. To investigate how jaw-muscle architecture and craniofacial position impact muscle performance during gouging, we combine skull and jaw-muscle architectural features to model muscle force production across a range of jaw gapes in these two species. We incorporate joint mechanics, resting sarcomere length and muscle architecture estimates from the masseter and temporalis to model muscle excursion, sarcomere length and relative tension as a function of joint angle. Muscle excursion from occlusion to an estimated maximum functional gape of 55 deg. was smaller in all regions of the masseter and temporalis of C. jacchus compared with S. oedipus except the posterior temporalis. As a consequence of reduced muscle excursion distributed over more sarcomeres in series (i.e. longer fibers), sarcomere length operating ranges are smaller in C. jacchus jaw muscles across this range of gapes. This configuration allows C. jacchus to act on a more favorable portion of the length—tension Curve at larger gapes and thereby generate relatively greater tension in these muscles compared with S. oedipus . Our results suggest that biting performance during tree gouging in common marmosets is improved by a musculoskeletal configuration that reduces muscle stretch at wide gapes while simultaneously facilitating comparatively large muscle forces at the extremes of jaw opening. * ASM : anterior superficial masseter AT : anterior temporalis DM : deep masseter L : muscle—tendon excursion L f : normalized muscle fiber length L f′ : measured muscle fiber length L m : muscle length L s : sarcomere length L s′ : measured sarcomere length L T : total tendon length L—T Curve : length—tension Curve M : mass MT : middle temporalis PCSA : physiological cross-sectional area PSM : posterior superficial masseter PT : posterior temporalis r : radius of the arc ROM : range of motion S n : sarcomere number ρ : density Φ : joint angular rotation θ : pennation angle
-
correlation between isometric force and intramuscular pressure in rabbit tibialis anterior muscle with an intact anterior compartment
Muscle & Nerve, 2009Co-Authors: Taylor M Winters, Richard L Lieber, Kenton R Kaufman, Genaro S Sepulveda, Patrick S Cottler, Samuel R WardAbstract:To determine the degree to which intramuscular pressure (IMP) and muscle force are correlated in an intact compartment, a custom pressure transducer was inserted into the rabbit tibialis anterior (TA) while activating the muscle via the peroneal nerve and measuring TA muscle force distal to the ankle retinaculum. In general, IMP was more variable compared to muscle force throughout the entire isometric Length-Tension relationship. In contrast to results obtained on isolated TA muscles, IMP-force relations with the compartment intact were not significantly different between the ascending and descending limbs of the Length-Tension Curve. Specifically, average relative pressure-force coefficients of determination (r2) were 0.76±0.11 for the active ascending limb and 0.98±0.01 for the active descending limb. These data demonstrate that muscle force and IMP are fairly well correlated under isometric conditions and that this relationship is not improved by measuring IMP in an intact environment.
-
architectural analysis and intraoperative measurements demonstrate the unique design of the multifidus muscle for lumbar spine stability
Journal of Bone and Joint Surgery American Volume, 2009Co-Authors: Samuel R Ward, Akihito Tomiya, Steven R Garfin, Lionel Gottschalk, Richard L LieberAbstract:Background: Muscular instability is an important risk factor for lumbar spine injury and chronic low-back pain. Although the lumbar multifidus muscle is considered an important paraspinal muscle, its design features are not completely understood. The purpose of the present study was to determine the architectural properties, in vivo sarcomere length operating range, and passive mechanical properties of the human multifidus muscle. We hypothesized that its architecture would be characterized by short fibers and a large physiological cross-sectional area and that it would operate over a relatively wide range of sarcomere lengths but would have very stiff passive material properties. Methods: The lumbar spines of eight cadaver specimens were excised en bloc from T12 to the sacrum. Multifidus muscles were isolated from each vertebral level, permitting the architectural measurements of mass, sarcomere length, normalized fiber length, physiological cross-sectional area, and fiber length-to-muscle length ratio. To determine the sarcomere length operating range of the muscle, sarcomere lengths were measured from intraoperative biopsy specimens that were obtained with the spine in the flexed and extended positions. The material properties of single muscle fibers were obtained from passive stress-strain tests of excised biopsy specimens. Results: The average muscle mass (and standard error) was 146 ± 8.7 g, and the average sarcomere length was 2.27 ± 0.06 μm, yielding an average normalized fiber length of 5.66 ± 0.65 cm, an average physiological cross-sectional area of 23.9 ± 3.0 cm2, and an average fiber length-to-muscle length ratio of 0.21 ± 0.03. Intraoperative sarcomere length measurements revealed that the muscle operates from 1.98 ± 0.15 μm in extension to 2.70 ± 0.11 μm in flexion. Passive mechanical data suggested that the material properties of the muscle are comparable with those of muscles of the arm or leg. Conclusions: The architectural design (a high cross-sectional area and a low fiber length-to-muscle length ratio) demonstrates that the multifidus muscle is uniquely designed as a stabilizer to produce large forces. Furthermore, multifidus sarcomeres are positioned on the ascending portion of the Length-Tension Curve, allowing the muscle to become stronger as the spine assumes a forward-leaning posture. Clinical Relevance: These findings demonstrate that the human multifidus muscle is designed to function as a dynamic stabilizer of the lumbar spine.
Thomas L Daniel - One of the best experts on this subject based on the ideXlab platform.
-
the length tension Curve in muscle depends on lattice spacing
Proceedings of The Royal Society B: Biological Sciences, 2013Co-Authors: David C Williams, Mary K Salcedo, Thomas C Irving, Michael Regnier, Thomas L DanielAbstract:Classic interpretations of the striated muscle length–tension Curve focus on how force varies with overlap of thin (actin) and thick (myosin) filaments. New models of sarcomere geometry and experiments with skinned synchronous insect flight muscle suggest that changes in the radial distance between the actin and myosin filaments, the filament lattice spacing, are responsible for between 20% and 50% of the change in force seen between sarcomere lengths of 1.4 and 3.4 µm. Thus, lattice spacing is a significant force regulator, increasing the slope of muscle's force–length dependence.
-
The length–tension Curve in muscle depends on lattice spacing
Proceedings. Biological sciences, 2013Co-Authors: C. David Williams, Mary K Salcedo, Thomas C Irving, Michael Regnier, Thomas L DanielAbstract:Classic interpretations of the striated muscle length–tension Curve focus on how force varies with overlap of thin (actin) and thick (myosin) filaments. New models of sarcomere geometry and experiments with skinned synchronous insect flight muscle suggest that changes in the radial distance between the actin and myosin filaments, the filament lattice spacing, are responsible for between 20% and 50% of the change in force seen between sarcomere lengths of 1.4 and 3.4 µm. Thus, lattice spacing is a significant force regulator, increasing the slope of muscle's force–length dependence.
-
cardiac like behavior of an insect flight muscle
The Journal of Experimental Biology, 2004Co-Authors: Thomas L DanielAbstract:The synchronous wing depressor muscles of the hawkmoth Manduca sexta undergo large amplitude motions at lengths that lie entirely on the ascending region of their twitch Length-Tension Curve. Moreover, these muscles bear a striking functional resemblance to mammalian cardiac muscle in both the shape of their Length-Tension Curve and in their working length range. Although operation on the ascending region of the twitch Length-Tension Curve sacrifices maximal force, it does permit the generation of larger forces at greater strains. In the case of cardiac muscle, this mechanical behavior is critical for accommodating the increasing stresses associated with greater ventricular filling. Similar characteristics in moth flight muscle suggest an analogous regulatory mechanism for skeletal muscles performing repetitive oscillatory work; the strong length dependence of force over their working length range should give the wing depressors the capacity to generate larger forces as wing stroke amplitude increases. These results support the notion that the Length-Tension relationship of muscle can be tuned to function in locomotor muscles.
Paul H Ratz - One of the best experts on this subject based on the ideXlab platform.
-
active tension adaptation at a shortened arterial muscle length inhibition by cytochalasin d
American Journal of Physiology-heart and Circulatory Physiology, 2011Co-Authors: Melissa L Bednarek, John E Speich, Amy S Miner, Paul H RatzAbstract:Unlike the static Length-Tension Curve of striated muscle, airway and urinary bladder smooth muscles display a dynamic Length-Tension Curve. Much less is known about the plasticity of the length-te...
-
Active tension adaptation at a shortened arterial muscle length: inhibition by cytochalasin-D.
American journal of physiology. Heart and circulatory physiology, 2011Co-Authors: Melissa L Bednarek, John E Speich, Amy S Miner, Paul H RatzAbstract:Unlike the static Length-Tension Curve of striated muscle, airway and urinary bladder smooth muscles display a dynamic Length-Tension Curve. Much less is known about the plasticity of the Length-Tension Curve of vascular smooth muscle. The present study demonstrates that there were significant increases of ∼15% in the phasic phase and ∼10% in the tonic phase of a third KCl-induced contraction of a rabbit femoral artery ring relative to the first contraction after a 20% decrease in length from an optimal muscle length (L(0)) to 0.8-fold L(0). Typically, three repeated contractions were necessary for full length adaptation to occur. The tonic phase of a third KCl-induced contraction was increased by ∼50% after the release of tissues from 1.25-fold to 0.75-fold L(o). The mechanism for this phenomenon did not appear to lie in thick filament regulation because there was no increase in myosin light chain (MLC) phosphorylation to support the increase in tension nor was length adaptation abolished when Ca(2+) entry was limited by nifedipine and when Rho kinase (ROCK) was blocked by H-1152. However, length adaptation of both the phasic and tonic phases was abolished when actin polymerization was inhibited through blockade of the plus end of actin by cytochalasin-D. Interestingly, inhibition of actin polymerization when G-actin monomers were sequestered by latrunculin-B increased the phasic phase and had no effect on the tonic phase of contraction during length adaptation. These data suggest that for a given level of cytosolic free Ca(2+), active tension in the femoral artery can be sensitized not only by regulation of MLC phosphatase via ROCK and protein kinase C, as has been reported by others, but also by a nonmyosin regulatory mechanism involving actin polymerization. Dysregulation of this form of active tension modulation may provide insight into alterations of large artery stiffness in hypertension.
-
Adjustable passive Length-Tension Curve in rabbit detrusor smooth muscle
Journal of applied physiology (Bethesda Md. : 1985), 2007Co-Authors: John E Speich, Christopher R. Dosier, Lindsey Borgsmiller, Kevin Quintero, Harry P. Koo, Paul H RatzAbstract:Until the 1990s, the passive and active Length-Tension (L-T) relationships of smooth muscle were believed to be static, with a single passive force value and a single maximum active force value for...