Myosin filaments have non-phosphorylated light chains in relaxed smooth muscle

Somlyo, Avril V.; Butler, Thomas M.; Bond, Meredith; Somlyo, Andrew P.

doi:10.1038/294567a0

Cited by 152 publications

(63 citation statements)

References 19 publications

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“…The presence of myosin filaments and cross-bridges in smooth muscle (A. P. Somlyo et ai., 1973;Ashton et al, 1975;A. V. Somlyo et al, 1981) is consistent with the sliding filament mechanism of contraction mediated by cyclic attachment of myosin cross-bridges to actin filaments, which has been characterized in striated muscle (A. F. Huxley and Niedergerke, 1954;H.…”

Section: Introductionmentioning

confidence: 57%

Cross-bridge kinetics, cooperativity, and negatively strained cross-bridges in vertebrate smooth muscle. A laser-flash photolysis study.

Somlyo

Goldman

Fujimori

et al. 1988

The Journal of General Physiology

138

106

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A B STR ACT The effects of laser-flash photolytic release of ATP from caged ATP [P3-1(2-nitrophenyl)ethyladenosine-5'-triphosphate] on stiffness and tension transients were studied in permeabilized guinea pig portal vein smooth muscle. During rigor, induced by removing ATP from the relaxed or contracting muscles, stiffness was greater than in relaxed muscle, and electron microscopy showed cross-bridges attached to actin filaments at an -45 ~ angle. In the absence of Ca 2+, liberation of ATP (0.1-1 mM) into muscles in rigor caused relaxation, with kinetics indicating cooperative reattachment of some crossbridges. Inorganic phosphate (Pi; 20 mM) accelerated relaxation. A rapid phase of force development, accompanied by a decline in stiffness and unaffected by 20 mM P~, was observed upon liberation of ATP in muscles that were released by 0.5-1.0% just before the laser pulse. This force increment observed upon detachment suggests that the cross-bridges can bear a negative tension. The second-order rate constant for detachment of rigor cross-bridges by ATP, in the absence of Ca 2+, was estimated to be 0.1-2.5 x 105 M-~s -~, which indicates that this reaction is too fast to limit the rate of ATP hydrolysis during physiological contractions. In the presence of Ca "+, force development occurred at a rate (0.4 s -~) similar to that of intact, electrically stimulated tissue. The rate of force development was an order of magnitude faster in muscles that had been thiophosphorylated with ATP~,S before the photochemical liberation of ATP, which indicates that under physiological conditions, in non-thiophosphorylated muscles, light-chain phosphorylation, rather than intrinsic properties of the actomyosin cross-bridges, limits the rate of force development. The release of micromolar ATP or CTP from caged ATP or caged CTP caused force development of up to 40% of maximal active tension in the absence of Ca 2+, consistent Address reprint requests to Dr. Avril V. Somlyo,

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Section: Introductionmentioning

confidence: 57%

Cross-bridge kinetics, cooperativity, and negatively strained cross-bridges in vertebrate smooth muscle. A laser-flash photolysis study.

Somlyo

Goldman

Fujimori

et al. 1988

The Journal of General Physiology

138

106

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“…However, this does not mean that dephosphorylation of the light chain will cause total dissolution of the thick filaments. Thick filaments have been found in relaxed, dephosphorylated muscles (10,12). Results from the present study also indicate that thick filaments exist in relaxed airway smooth muscle, even after removal of extracellular calcium and in the presence of the calcium-chelating agent EGTA.…”

Section: Discussionmentioning

confidence: 99%

Influence of calcium on myosin thick filament formation in intact airway smooth muscle

Herrera

Kuo

Seow

2002

American Journal of Physiology-Cell Physiology

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Myosin thick filaments have been shown to be structurally labile in intact smooth muscles. Although the mechanism of thick filament assembly/disassembly for purified myosins in solution has been well described, regulation of thick filament formation in intact muscle is still poorly understood. The present study investigates the effect of resting calcium level on thick filament maintenance in intact airway smooth muscle and on thick filament formation during activation. Cross-sectional density of the thick filaments measured electron microscopically showed that the density increased substantially (144%) when the muscle was activated. The abundance of filamentous myosins in relaxed muscle was calcium sensitive; in the absence of calcium (with EGTA), the filament density deceased by 35%. Length oscillation imposed on the muscle under zero-calcium conditions produced no further reduction in the density. Isometric force and filament density recovered fully after reincubation of the muscle in normal physiological saline. The results suggest that in airway smooth muscle, filamentous myosins exist in equilibrium with monomeric myosins; muscle activation favors filament formation, and the resting calcium level is crucial for preservation of the filaments in the relaxed state. electron microscopy; muscle contraction; ethylene glycolbis(␤-aminoethyl ether)-N,N,NЈ,NЈ-tetraacetic acid; muscle plasticity IT HAS BEEN SUGGESTED that myosin thick filaments in relaxed smooth muscle are partially dissolved and reaggregate upon activation (2,3,14,15). Functional studies of airway smooth muscle have shown that thick filament lengthening could account for the increase in isometric force and the decrease in shortening velocity during the sustained phase of contraction (9). It was observed in airway smooth muscle that within at least a threefold length range and when the muscle was allowed to adapt to the lengths at which it was studied, isometric force was independent of muscle length, and shortening velocity and power output were positively correlated to muscle length (7). The observations suggest that the number of in-series contractile units (of which myosin thick filaments are an essential component) could be variable. We observed in a recent study that the thick filaments in intact airway smooth muscle dissolved partially when subjected to mechanical perturbation (5). There are, therefore, many lines of evidence supporting a notion that myosin thick filaments in smooth muscle are labile; partial disassembly/reassembly of the thick filaments could allow the muscle to quickly adapt to externally imposed mechanical strains that reshape the cell. As a first step toward understanding what regulates cellular plasticity in terms of thick filament formation, the present study was carried out to examine myosin evanescence during activation and to determine the stability of the thick filaments in relaxed airway smooth muscle depleted of calcium and subjected to mechanical perturbation. METHODS Tissue PreparationPorcine tracheal smooth musc...

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“…Because folded myosin cannot form thick filament, it has been hypothesized that phosphorylation could dynamically control filament assembly in certain cell types (7,13), whereas assembly͞disassembly is unlikely to play a major role in regulating the contraction͞relaxation cycle in smooth muscle cells (40,41). Several studies have revealed the molecular basis of the conformational transition which is unique to smooth muscle and nonmuscle myosins.…”

Section: Discussionmentioning

confidence: 99%

The motor domain and the regulatory domain of myosin solely dictate enzymatic activity and phosphorylation-dependent regulation, respectively

Sata

Stafford

Mabuchi

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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While the structures of skeletal and smooth muscle myosins are homologous, they differ functionally from each other in several respects, i.e., motor activities and regulation. To investigate the molecular basis for these differences, we have produced a skeletal͞smooth chimeric myosin molecule and analyzed the motor activities and regulation of this myosin. The produced chimeric myosin is composed of the globular motor domain of skeletal muscle myosin (Met 1 -Gly 773 ) and the C-terminal long ␣-helix domain of myosin subfragment 1 as well as myosin subfragment 2 (Gly 773 -Ser 1104 ) and light chains of smooth muscle myosin. Both the actin-activated ATPase activity and the actin-translocating activity of the chimeric myosin were completely regulated by light chain phosphorylation. On the other hand, the maximum actin-activated ATPase activity of the chimeric myosin was the same as skeletal myosin and thus much higher than smooth myosin. These results show that the C-terminal light chainassociated domain of myosin head solely confers regulation by light chain phosphorylation, whereas the motor domain determines the rate of ATP hydrolysis. This is the first report, to our knowledge, that directly determines the function of the two structurally separated domains in myosin head.

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Myosin filaments have non-phosphorylated light chains in relaxed smooth muscle

Cited by 152 publications

References 19 publications

Cross-bridge kinetics, cooperativity, and negatively strained cross-bridges in vertebrate smooth muscle. A laser-flash photolysis study.

Cross-bridge kinetics, cooperativity, and negatively strained cross-bridges in vertebrate smooth muscle. A laser-flash photolysis study.

Influence of calcium on myosin thick filament formation in intact airway smooth muscle

The motor domain and the regulatory domain of myosin solely dictate enzymatic activity and phosphorylation-dependent regulation, respectively

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