Effects of intracellular acidosis on Ca2+ activation, contraction, and relaxation of frog skeletal muscle

1995 ◽  
Vol 268 (1) ◽  
pp. C55-C63 ◽  
Author(s):  
A. J. Baker ◽  
R. Brandes ◽  
M. W. Weiner
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Frog Skeletal Muscle ◽  
Intracellular Acidosis ◽  
Tetanic Force ◽  
Force Relaxation ◽  
Cross Bridges ◽  
Contraction And Relaxation ◽  
Initial Force ◽  
Force Relationship

The goal of this study was to determine the effects of intracellular acidosis (pH approximately 6.3) of frog skeletal muscle on force and on intracellular Ca2+ concentration ([Ca2+]i; measured at 20 degrees C using indo 1 fluorescence). Acidosis reduced tetanic force by only 11 +/- 2% (mean +/- SE, n = 8) but increased tetanic [Ca2+]i by 33 +/- 6%, suggesting that acidosis reduced the maximum Ca(2+)-activated force. During relaxation, the [Ca2+]i at half-maximal force was doubled with acidosis, suggesting that acidosis altered the Ca(2+)-force relationship. Acidosis markedly slowed force relaxation and [Ca2+]i decline (time constants fitted to force and [Ca2+]i during relaxation increased by 133 +/- 20 and 68 +/- 13%, respectively, with acidosis), suggesting that slowed force relaxation with acidosis may arise from slowed Ca2+ clearance from the cytosol. Late in relaxation, at approximately 30% of initial force, there was a transient phase of [Ca2+]i increase that was delayed with acidosis in proportion to the slowing of force relaxation. This is consistent with previous suggestions that dissociation of cross-bridges from the thin filament during relaxation promotes Ca2+ release to the cytosol from troponin. This study concludes that in skeletal muscle acidosis has little effect on tetanic force and that the major effects are decreased Ca2+ sensitivity and slower relaxation.

scholarly journals Intensity changes of the first and second thin-filament layer-lines of a frog skeletal muscle during isometric contraction

2000 ◽  
Vol 40 (supplement) ◽  
pp. S64
Author(s):  
Y. Takezawa ◽  
T. Kobayashi ◽  
Y. Sugimoto ◽  
K. Wakabayashi
Keyword(s):  
Skeletal Muscle ◽  
Isometric Contraction ◽  
Thin Filament ◽  
Frog Skeletal Muscle ◽  
Intensity Changes

Intracellular tetanic calcium signals are reduced in fatigue of whole skeletal muscle

1993 ◽  
Vol 264 (3) ◽  
pp. C577-C582 ◽  
Author(s):  
A. J. Baker ◽  
M. C. Longuemare ◽  
R. Brandes ◽  
M. W. Weiner
Keyword(s):  
Skeletal Muscle ◽  
Intracellular Calcium ◽  
Calcium Handling ◽  
Tetanic Stimulation ◽  
Muscle Contractility ◽  
Calcium Signals ◽  
Tetanic Force ◽  
Force Relaxation ◽  
Calcium Removal ◽  
Whole Muscle

Force and intracellular calcium signals were monitored in whole bullfrog semitendinosus muscles during fatigue produced by intermittent tetanic stimulation. Intracellular calcium signals were monitored using the fluorescent calcium-sensitive indicator indo-1 from the ratio of fluorescence intensities (R) at 400 and 470 nm. Fatiguing stimulation caused 1) proportional decreases of tetanic force and R, suggesting a component of the decreased force during fatigue of whole muscle may be due to insufficient calcium to activate contraction; 2) a progressive slowing of the relaxation of both force and R, suggesting slowed force relaxation may be mediated by slowed calcium removal from the myoplasm; 3) an increase of resting level R, suggesting impaired calcium removal from, or increased leakage to the cytosol; 4) prolongation of the twitch contraction, which was paralleled by changes in R. These findings are consistent with previous single fiber studies and suggest that changes in whole muscle contractility with fatigue may be partially mediated by changes in calcium handling by the cell.

scholarly journals Enhanced Ca2+ transport and muscle relaxation in skeletal muscle from sarcolipin-null mice

2011 ◽  
Vol 301 (4) ◽  
pp. C841-C849 ◽  
Author(s):  
A. Russell Tupling ◽  
Eric Bombardier ◽  
Subash C. Gupta ◽  
Dawar Hussain ◽  
Chris Vigna ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Relaxation ◽  
Force Frequency ◽  
Relaxation Rates ◽  
Wild Type ◽  
Inhibitory Effects ◽  
Tetanic Force ◽  
Plasmic Reticulum ◽  
Force Relaxation ◽  
Frequency Curves

Sarcolipin (SLN) inhibits sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) pumps. To evaluate the physiological significance of SLN in skeletal muscle, we compared muscle contractility and SERCA activity between Sln-null and wild-type mice. SLN protein expression in wild-type mice was abundant in soleus and red gastrocnemius (RG), low in extensor digitorum longus (EDL), and absent from white gastrocnemius (WG). SERCA activity rates were increased in soleus and RG, but not in EDL or WG, from Sln-null muscles, compared with wild type. No differences were seen between wild-type and Sln-null EDL muscles in force-frequency curves or maximum rates of force development (+dF/d t). Maximum relaxation rates (−dF/d t) of EDL were higher in Sln-null than wild type across a range of submaximal stimulation frequencies, but not during a twitch or peak tetanic contraction. For soleus, no differences were seen between wild type and Sln-null in peak tetanic force or +dF/d t; however, force-frequency curves showed that peak force during a twitch and 10-Hz contraction was lower in Sln-null. Changes in the soleus force-frequency curve corresponded with faster rates of force relaxation at nearly all stimulation frequencies in Sln-null compared with wild type. Repeated tetanic stimulation of soleus caused increased (−dF/d t) in wild type, but not in Sln-null. No compensatory responses were detected in analysis of other Ca2+ regulatory proteins using Western blotting and immunohistochemistry or myosin heavy chain expression using immunofluorescence. These results show that 1) SLN regulates Ca2+-ATPase activity thereby regulating contractile kinetics in at least some skeletal muscles, 2) the functional significance of SLN is graded to the endogenous SLN expression level, and 3) SLN inhibitory effects on SERCA function are relieved in response to repeated contractions thus enhancing relaxation rates.

scholarly journals Troponin and Titin Coordinately Regulate Length-dependent Activation in Skinned Porcine Ventricular Muscle

2008 ◽  
Vol 131 (3) ◽  
pp. 275-283 ◽  
Author(s):  
Takako Terui ◽  
Munguntsetseg Sodnomtseren ◽  
Douchi Matsuba ◽  
Jun Udaka ◽  
Shin'ichi Ishiwata ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Left Ventricular ◽  
Ventricular Muscle ◽  
Passive Force ◽  
Active Force ◽  
Fast Skeletal Muscle ◽  
Thin Filaments ◽  
Cross Bridges ◽  
Length Dependent Activation

We investigated the molecular mechanism by which troponin (Tn) regulates the Frank-Starling mechanism of the heart. Quasi-complete reconstitution of thin filaments with rabbit fast skeletal Tn (sTn) attenuated length-dependent activation in skinned porcine left ventricular muscle, to a magnitude similar to that observed in rabbit fast skeletal muscle. The rate of force redevelopment increased upon sTn reconstitution at submaximal levels, coupled with an increase in Ca2+ sensitivity of force, suggesting the acceleration of cross-bridge formation and, accordingly, a reduction in the fraction of resting cross-bridges that can potentially produce additional active force. An increase in titin-based passive force, induced by manipulating the prehistory of stretch, enhanced length-dependent activation, in both control and sTn-reconstituted muscles. Furthermore, reconstitution of rabbit fast skeletal muscle with porcine left ventricular Tn enhanced length-dependent activation, accompanied by a decrease in Ca2+ sensitivity of force. These findings demonstrate that Tn plays an important role in the Frank-Starling mechanism of the heart via on–off switching of the thin filament state, in concert with titin-based regulation.

scholarly journals Effects of ramp shortening during linear phase of relaxation on [Ca2+]i in intact skeletal muscle fibers

1999 ◽  
Vol 276 (1) ◽  
pp. C152-C160 ◽  
Author(s):  
Yandong Jiang ◽  
Fred J. Julian
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Sarcomere Length ◽  
Muscle Fibers ◽  
Linear Phase ◽  
Fixed Size ◽  
Skeletal Muscle Fibers ◽  
Straight Line ◽  
Sigmoidal Curve ◽  
Cross Bridges

The effects of shortening distance at V u, the unloaded shortening speed, and filament overlap on the amount of extra Ca2+ released during relaxation in muscle, as indicated by the bump area, were studied. Single, intact frog skeletal muscle fibers at 3°C were used. The myoplasmic free Ca2+ concentration ([Ca2+]i) was estimated by using fura 2 salt injected into the myoplasm. Ramps were applied, either at full overlap with different sizes or at varying overlaps with a fixed size, in the linear phase of relaxation. At full overlap, a plot of bump area vs. ramp size was fit by using a sigmoidal curve with one-half of the bump area equal to 25.9 nm. With a fixed ramp size of 100 nm/half-sarcomere, the plot of bump area vs. mean sarcomere length (SLm) was fit by a straight line intersecting the SLm axis at ∼3.5 μm, close to just no overlap. The results suggest that the transition in the distribution of attached cross bridges from the isometric case to one appropriate for unloaded shortening at V u is completed within 50 nm/half-sarcomere and support the view that attached cross bridges in the overlap zone influence the affinity of Ca2+for troponin C in the thin filament.

Aminophylline enhances contractility of frog skeletal muscle: an effect dependent on extracellular calcium

1989 ◽  
Vol 67 (2) ◽  
pp. 671-676 ◽  
Author(s):  
J. W. Ridings ◽  
S. R. Barry ◽  
J. A. Faulkner
Keyword(s):  
Skeletal Muscle ◽  
Ringer Solution ◽  
Force Transducer ◽  
Extracellular Calcium ◽  
Semitendinosus Muscle ◽  
Tetanic Force ◽  
Isometric Twitch ◽  
Force Relationship ◽  
Normal Ringer

The effects of aminophylline (10–500 microM) on isometric twitch and tetanic forces were studied in vitro on frog semitendinosus muscle. Two hypotheses were tested: 1) that micromolar concentrations of aminophylline enhanced contractility of isolated skeletal muscle and 2) that the potentiating effect of aminophylline was dependent on the presence of extracellular calcium ions. Muscles were removed, placed in aerated Ringer solution at 20 degrees C, attached to a force transducer, and stimulated directly. Muscles in normal Ringer and aminophylline Ringer were compared throughout the frequency-force relationship from twitches to maximum tetanic force. Aminophylline increased twitch force significantly at concentrations as low as 25 microM. Over a range of stimulation frequencies, but especially at 10 and 20 Hz, aminophylline increased tetanic force. The potentiating effect of aminophylline (100 microM) was reduced or eliminated in calcium-free Ringer containing 10 mM magnesium. We conclude that aminophylline, at therapeutic concentrations, enhances muscle contractility, and the enhancement is dependent on the presence of extracellular calcium. These findings support the concept that aminophylline is effective in improving respiration in humans with airway obstruction by enhancing diaphragmatic contractility.

scholarly journals Structural Changes of Cross-Bridges on Transition from Isometric to Shortening State in Frog Skeletal Muscle

2006 ◽  
Vol 91 (11) ◽  
pp. 4110-4120 ◽  
Author(s):  
Naoto Yagi ◽  
Hiroyuki Iwamoto ◽  
Katsuaki Inoue
Keyword(s):  
Skeletal Muscle ◽  
Structural Changes ◽  
Frog Skeletal Muscle ◽  
Cross Bridges
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