scholarly journals Myofilament-generated tension oscillations during partial calcium activation and activation dependence of the sarcomere length-tension relation of skinned cardiac cells.

1978 ◽  
Vol 72 (5) ◽  
pp. 667-699 ◽  
Author(s):  
A Fabiato ◽  
F Fabiato
Keyword(s):  
Sarcomere Length ◽  
Rapid Decrease ◽  
Cardiac Cells ◽  
Maximal Velocity ◽  
Active Tension ◽  
Velocity Of Shortening ◽  
Rigor Tension ◽  
The Mean ◽  
Rat Ventricle ◽  
Full Activation

During partial Ca2+ activation, skinned cardiac cells with sarcoplasmic reticulum destroyed by detergent developed spontaneous tension oscillations consisting of cycles (0.1-1 Hz) of rapid decrease of tension corresponding to the yield of some sarcomeres and slow redevelopment of tension corresponding to the reshortening of these sarcomeres. Such myofilament-generated tension oscillations were never observed during the full activation induced by a saturating [free Ca2+] or during the rigor tension induced by decreasing [MgATP] in the absence of free Ca2+ or when the mean sarcomere length (SL) of the preparation was greater than 3.10 microm during partial Ca2+ activation. A stiff parallel elastic element borne by a structure that could be digested by elastase hindered the study of the SL--active tension diagram in 8-13-microm-wide skinned cells from the rat ventricle, but this study was possible in 2-7-microm-wide myofibril bundles from the frog or dog ventricle. During rigor the tension decreased linearly when SL was increased from 2.35 to 3.80 microm. During full Ca2+ activation the tension decreased by less than 20% when SL was increased from 2.35 to approximately 3.10 microm. During partial Ca2+ activation the tension increased when SL was increased from 2.35 to 3.00 microm. From this observation of an apparent increase in the sensitivity of the myofilaments to Ca2+ induced by increasing SL during partial Ca2+ activation, a model was proposed that describes the tension oscillations and permits the derivation of the maximal velocity of shortening (Vmax). Vmax was increased by increasing [free Ca2+] or decreasing [free Mg2+] but not by increasing SL.

Direct observation of radial intracellular P O 2 gradients in a single cardiomyocyte of the rat

1998 ◽  
Vol 275 (1) ◽  
pp. H225-H233 ◽  
Author(s):  
Eiji Takahashi ◽  
Keiko Sato ◽  
Hiroshi Endoh ◽  
Zhe-Long Xu ◽  
Katsuhiko Doi
Keyword(s):  
Oxygen Consumption ◽  
Cardiac Cells ◽  
Facilitated Diffusion ◽  
Single Individual ◽  
Radial Profiles ◽  
Carbonyl Cyanide ◽  
Increase Oxygen Consumption ◽  
The Mean ◽  
Rat Ventricle

The purpose of the present study was to directly visualize radial gradients of intracellular [Formula: see text] in a single individual cardiomyocyte isolated from the rat ventricle. Microspectrophotometry with the use of cytosolic myoglobin as an oxygen probe was conducted at 410 nm. When the quiescent cell was incubated with 1 μM carbonyl cyanide m-chlorophenylhydrazone to increase oxygen consumption approximately eightfold, gradual decreases in myoglobin oxygen saturation (SMb) were demonstrated toward the core of the cell, whereas these decreases disappeared when the cell was treated with 2 mM NaCN. These results highlighted the importance of diffusional oxygen transport in determining intracellular oxygenation in cardiac cells. From the measured SMb, we assessed the profile of radial changes in intracellular [Formula: see text]at the mean SMb comparable to that in vivo (∼0.5). Quite steep [Formula: see text]gradients were demonstrated in the vicinity of the sarcolemma that were rapidly attenuated toward the cell core. These radial profiles of intracellular [Formula: see text] demonstrate the significance of myoglobin-facilitated diffusion of oxygen. Furthermore, the shallow gradients of [Formula: see text] near the center of the cell might arise from partial depression of oxygen consumption near the cell core.

Diffusion and electrogenic components of the resting potential in explanted neonatal rat ventricle cells

1987 ◽  
Vol 65 (10) ◽  
pp. 2110-2116
Author(s):  
Martine LeFloch ◽  
Otto F. Schanne ◽  
Elena Ruiz-Ceretti
Keyword(s):  
Cardiac Cells ◽  
Neonatal Rat ◽  
Resting Potential ◽  
Channel Blockers ◽  
Ca Channel ◽  
High K ◽  
The Mean ◽  
The Difference ◽  
Rat Ventricle ◽  
Steady Potential

Spontaneously beating explanted neonatal rat ventricle cells stop beating and show a steady potential (the mean resting potential, −46.2 mV at 6.0 mM Ko) when exposed to 10 mM Cao or 4 mM Mn. When Ko was increased, resting potential changed only slightly between 3 and 15 mM, but the resting potential versus Ko characteristically approached the slope of a K electrode at high Ko Elimination of Cl from the medium did not alter the K dependence of the resting potential. However, a hyperpolarization of 9 mV per 10-fold change was observed when Nao was decreased from 50 to 4 mM. Ouabain (10−4 M) depolarized the membrane within 2 min to a stable level of about −30 mV in spontaneously beating cells and in those treated with Ca channel blockers. This potential was considered as the diffusion component of the membrane potential, Vdiff. Consequently the difference between resting potential and Vdiff represents the ouabain-sensitive or the electrogenic component of the resting potential. Using linearized versions of the Mullins and Noda as well as the Goldman – Hodgkin – Katz equations, we calculated that a PNa/PK between 0.25 and 0.35, a Na/K exchange ratio of 2.0, and a Ki of 160 mM adequately described the K dependence of the resting potential. We demonstrated the contribution of electrogenic Na extrusion to the resting potential of mammalian cardiac cells in culture. Therefore the existence of a composite resting potential precludes the direct comparison of potential measurements obtained under conditions liable to independently modify either the diffusion or the electrogenic component.

Stretch-induced growth in chicken wing muscles: myofibrillar proliferation

1981 ◽  
Vol 241 (3) ◽  
pp. C93-C97 ◽  
Author(s):  
C. R. Ashmore ◽  
P. J. Summers
Keyword(s):  
Electron Microscopy ◽  
Sarcomere Length ◽  
Experimental Period ◽  
Active Tension ◽  
Sectional Area ◽  
Cross Sectional ◽  
Mean Diameter ◽  
Rna And Protein Synthesis ◽  
Sarcotubular System ◽  
The Mean

The patigialis muscle (PAT) in the wing of the chicken can be induced to grow rapidly in length and in diameter by passively stretching the muscle with a spring-loaded aluminum bar (Holly et al., Am. J. Physiol. 238 (Cell Physiol. 7): C62–C71, 1980). Rates of DNA, RNA, and protein synthesis are accelerated. Sarcomere length falls from 3.19 micrometers after 1 day of stretch to only 10% above control values at 7 days of stretch. Myofibrils are wavy and misaligned. Electron microscopy of cross-sectioned muscles shows that the fraction of cell volume occupied by myofibrils remains constant throughout the experimental period, even though cross-sectional area of the muscle fibers increases by 55%. The mean diameter of myofibrils in stretched muscle increases by more than 25%. The number of splitting myofibrils increases from 15% before stretching to 45% after 1 wk of stretch. Splits appear to originate in the center of the I band, and then progress to the A band and the periphery of the myofibril. Elements of the sarcotubular system develop quickly at the origin of the fractures. It is concluded that rapid growth of the myofibril is required for initiation of splitting. Neither neurally mediated active tension nor muscle contraction are required.

Mechanical load-dependent regulation of satellite cell and fiber size in rat soleus muscle

2006 ◽  
Vol 290 (4) ◽  
pp. C981-C989 ◽  
Author(s):  
X. D. Wang ◽  
F. Kawano ◽  
Y. Matsuoka ◽  
K. Fukunaga ◽  
M. Terada ◽  
...  
Keyword(s):  
Satellite Cell ◽  
Muscle Fiber ◽  
Satellite Cells ◽  
Central Region ◽  
Sarcomere Length ◽  
Sectional Area ◽  
Cross Sectional ◽  
Fiber Properties ◽  
Rat Soleus Muscle ◽  
The Mean

The effects of mechanical unloading and reloading on the properties of rat soleus muscle fibers were investigated in male Wistar Hannover rats. Satellite cells in the fibers of control rats were distributed evenly throughout the fiber length. After 16 days of hindlimb unloading, the number of satellite cells in the central, but not the proximal or distal, region of the fiber was decreased. The number of satellite cells in the central region gradually increased during the 16-day period of reloading. The mean sarcomere length in the central region of the fibers was passively shortened during unloading due to the plantarflexed position at the ankle joint: sarcomere length was maintained at <2.1 μm, which is a critical length for tension development. Myonuclear number and domain size, fiber cross-sectional area, and the total number of mitotically active and quiescent satellite cells of whole muscle fibers were lower than control fibers after 16 days of unloading. These values then returned to control values after 16 days of reloading. These results suggest that satellite cells play an important role in the regulation of muscle fiber properties. The data also indicate that the satellite cell-related regulation of muscle fiber properties is dependent on the level of mechanical loading, which, in turn, is influenced by the mean sarcomere length. However, it is still unclear why the region-specific responses, which were obvious in satellite cells, were not induced in myonuclear number and fiber cross-sectional area.

Comparative force-velocity relation and analyses of myosin of dog atria and ventricles

1982 ◽  
Vol 243 (3) ◽  
pp. H391-H397 ◽  
Author(s):  
J. Wikman-Coffelt ◽  
H. Refsum ◽  
G. Hollosi ◽  
L. Rouleau ◽  
L. Chuck ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Calcium Concentration ◽  
Maximum Velocity ◽  
Calcium Sensitivity ◽  
Myofibrillar Proteins ◽  
Maximal Velocity ◽  
Velocity Of Shortening ◽  
Force Velocity ◽  
Normal Calcium ◽  
Actin Concentration

The isolated muscle and purified myofibrillar proteins of canine atria and ventricles were compared relative to force-velocity relations and rate of adenosine 5'-triphosphatase (ATPase) activity as a function of calcium concentrations. The maximal stress development of isolated trabeculae of canine atria was similar to that of canine right ventricular papillary muscles when analyzed at saturating calcium concentrations (7.5 mM); however, stress was less in the atria when studied at normal calcium concentrations (2.5 mM). The maximal velocity of shortening of atrial trabeculae was about 2.3 times higher than that of ventricular muscle. Regulated actomyosin characterized from the myofibrillar proteins of the two tissues gave directionally similar calcium sensitivity. The maximum velocity of shortening for actin-activated atrial myosin of the dog was approximately 1.8 times higher when the latter was analyzed as a function of actin concentration. Both maximal tension of isolated muscle and regulated actomyosin ATPase activity were dependent on calcium concentration.

Dependence of the contractile activation of skinned cardiac cells on the sarcomere length

Nature ◽  
1975 ◽  
Vol 256 (5512) ◽  
pp. 54-56 ◽  
Author(s):  
ALEXANDRE FABIATO ◽  
FRANÇOISE FABIATO
Keyword(s):  
Sarcomere Length ◽  
Cardiac Cells ◽  
Contractile Activation

Tracheal smooth muscle mechanics in vivo

1990 ◽  
Vol 68 (1) ◽  
pp. 209-219 ◽  
Author(s):  
M. Okazawa ◽  
P. Pare ◽  
J. Road
Keyword(s):  
Smooth Muscle ◽  
Muscle Mechanics ◽  
Muscle Length ◽  
Base Line ◽  
Maximal Velocity ◽  
Velocity Of Shortening ◽  
Length Changes ◽  
Trachealis Muscle

We applied the technique of sonomicrometry to directly measure length changes of the trachealis muscle in vivo. Pairs of small 1-mm piezoelectric transducers were placed in parallel with the muscle fibers in the posterior tracheal wall in seven anesthetized dogs. Length changes were recorded during mechanical ventilation and during complete pressure-volume curves of the lung. The trachealis muscle showed spontaneous fluctuations in base-line length that disappeared after vagotomy. Before vagotomy passive pressure-length curves showed marked hysteresis and length changed by 18.5 +/- 13.2% (SD) resting length at functional residual capacity (LFRC) from FRC to total lung capacity (TLC) and by 28.2 +/- 16.2% LFRC from FRC to residual volume (RV). After vagotomy hysteresis decreased considerably and length now changed by 10.4 +/- 3.7% LFRC from FRC to TLC and by 32.5 +/- 14.6% LFRC from FRC to RV. Bilateral supramaximal vagal stimulation produced a mean maximal active shortening of 28.8 +/- 14.2% resting length at any lung volume (LR) and shortening decreased at lengths above FRC. The mean maximal velocity of shortening was 4.2 +/- 3.9% LR.S-1. We conclude that sonomicrometry may be used to record smooth muscle length in vivo. Vagal tone strongly influences passive length change. In vivo active shortening and velocity of shortening are less than in vitro, implying that there are significant loads impeding shortening in vivo.

scholarly journals Quasar Evolution and the Growth of Black Holes in the Nuclei of Active Galaxies

1989 ◽  
Vol 134 ◽  
pp. 233-239
Author(s):  
R. D. Blandford
Keyword(s):  
Black Holes ◽  
Active Galactic Nuclei ◽  
Radiation Pressure ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Rapid Decrease ◽  
Active Galaxies ◽  
Host Galaxy ◽  
Nearby Galaxies ◽  
The Mean

The observed evolutionary behavior of active galactic nuclei is compatible with a model in which black holes form in the nuclei of new-born galaxies and then grow at a rate limited by both radiation pressure and the supply of gas. Individual sources become more luminous with time as long as they are being fueled. However, the rapid decrease in the mean rate of supply of gas causes a strong decline in the space density of active objects. Nearby galaxies should harbor modest size (∼ 106 – 108 M⊙) black holes. It is suggested that the gas that fuels high redshift quasars is mostly derived from the host galaxy.

scholarly journals Energy balance studies in frog skeletal muscles shortening at one-half maximal velocity.

1984 ◽  
Vol 84 (3) ◽  
pp. 347-359 ◽  
Author(s):  
E Homsher ◽  
T Yamada ◽  
A Wallner ◽  
J Tsai
Keyword(s):  
Skeletal Muscles ◽  
Maximum Velocity ◽  
High Energy ◽  
Sartorius Muscle ◽  
Maximal Velocity ◽  
High Energy Phosphate ◽  
The Mean ◽  
S Period ◽  
High Energy Phosphate Metabolism ◽  
Frog Sartorius

High-energy phosphate metabolism and energy liberated as heat and work were measured in 3-s tetani of frog sartorius muscle at 0 degree C. Two contraction periods were studied: (a) a 0.35-s period of shortening near half-maximum velocity beginning after 2 s of isometric stimulation, and (b) a 0.65-s isometric period immediately following the shortening. There were no significant changes in levels of ATP, ADP, or AMP in the two contraction periods. The observed changes in inorganic phosphate and creatine levels indicated that the only significant reaction occurring was phosphocreatine splitting. The mean rate of high-energy phosphate splitting during the shortening, 1.60 +/- 0.23 mumol X g-1 X s-1 (n = 24), was about fivefold higher than that in the 1-s period in the isometric tetanus, 0.32 +/- 0.11 mumol X g-1 X s-1 (n = 17), observed in our previous study. The mean rate in the post-shortening period, 0.46 +/- 0.13 mumol X g-1 X s-1 (n = 17), was not significantly different from that in the 1-s period in the isometric tetanus. A large amount of heat plus work was produced during the shortening period, and this could be accounted for by simultaneous chemical changes. In the post-shortening period, the observed enthalpy was also accounted for by simultaneous chemical reactions. Thus, the present result is in sharp contrast to that obtained from a similar study performed at a shortening at Vmax, where an enthalpy excess was produced during shortening and an enthalpy deficit was produced during the period following the shortening.

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