Length dependence of Ca(2+)-tension relationship in aequorin-injected ferret papillary muscles

1997 ◽  
Vol 273 (3) ◽  
pp. H1068-H1074 ◽  
Author(s):  
K. Komukai ◽  
S. Kurihara
Keyword(s):  
Troponin I ◽  
Muscle Length ◽  
Repetitive Stimulation ◽  
Papillary Muscles ◽  
Tetanic Contraction ◽  
C Protein ◽  
Length Dependence ◽  
Dependent Change ◽  
Maximal Tension ◽  
The Relationship

The possible contractile proteins, which are related to the length-dependent change in the relationship between intracellular Ca2+ concentration ([Ca2+]i) and tension, were investigated using aequorin-injected ferret papillary muscles. Tetanic contraction was produced by applying repetitive stimulation to the ryanodine-treated preparations, and the relationships between [Ca2+]i and tension were measured. When the muscle length was decreased from maximal length (Lmax), at which maximal tension is produced, to 95 and 90% Lmax, the maximal tension was significantly decreased. [Ca2+]i required for producing 50% of the maximal tension was significantly increased from 1.05 +/- 0.04 microM (Lmax) to 1.17 +/- 0.04 microM (95% Lmax) and to 1.22 +/- 0.04 microM (90% Lmax). Isoproterenol (Iso) accentuated the length-dependent change in the [Ca2+]i-tension relationship. The decrease in the Ca2+ sensitivity induced by Iso was larger at shorter muscle lengths compared with that at Lmax. It is, therefore, suggested that adenosine 3',5'-cyclic monophosphate-dependent phosphorylation of troponin I and/or C protein alters the length dependence of the [Ca2+]i-tension relationship and that troponin I and/or C protein might be involved in the length-tension-dependent change in the affinity of the contractile elements for Ca2+.

Relation between contractile function and regulatory cardiac proteins in hypertrophied hearts

1996 ◽  
Vol 270 (6) ◽  
pp. H2021-H2028 ◽  
Author(s):  
B. Stein ◽  
S. Bartel ◽  
U. Kirchhefer ◽  
S. Kokott ◽  
E. G. Krause ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Troponin I ◽  
Contractile Function ◽  
Papillary Muscles ◽  
Camp Accumulation ◽  
Adrenergic Stimulation ◽  
Beta Adrenergic ◽  
C Protein ◽  
Camp Formation ◽  
Phosphate Incorporation

The aim of this study was to examine the mechanism(s) underlying the reduced isoproterenol-induced positive inotropic and lusitropic effects in hypertrophied hearts. Chronic beta-adrenergic stimulation (2.4 mg isoproterenol.kg-1. day-1 for 4 days) induced cardiac hypertrophy by 33 +/- 2% in rats. A parallel downregulation of phospholamban (PLB) and sarcoplasmic reticulum Ca2(+)-ATPase (SERCA2) protein expression by 49 and 40%, respectively, was observed, whereas troponin I (TNI) and C protein remained unchanged. In papillary muscles from chronically beta-adrenergically stimulated rats, the isoproterenol-induced positive inotropic and lusitropic effects, as well as adenosine 3',5'-cyclic monophosphate (cAMP) accumulation, were attenuated compared with those in control animals. Acute exposure to isoproterenol induced phosphate incorporation into PLB, TNI, and C protein of 48 +/- 4.6, 55 +/- 5.0, and 27 +/- 4.9 pmol/mg homogenate protein, respectively, in control animals. In the hypertrophied hearts, phosphate incorporation into PLB was reduced by 76%, whereas phosphate incorporation into TNI or C protein remained unchanged. In conclusion, chronic beta-adrenergic stimulation reduced the isoproterenol-stimulated positive inotropic and lusitropic effects in papillary muscles, which were accompanied by 1) diminished cAMP formation, 2) attenuation of cAMP-mediated PLB phosphorylation, and 3) downregulation of PLB and SERCA2 protein.

scholarly journals Reports of the length dependence of fatigue are greatly exaggerated

2006 ◽  
Vol 101 (1) ◽  
pp. 23-29 ◽  
Author(s):  
M. B. MacNaughton ◽  
B. R. MacIntosh
Keyword(s):  
Muscle Length ◽  
Repetitive Stimulation ◽  
Double Pulse ◽  
Medial Gastrocnemius ◽  
Passive Force ◽  
Active Force ◽  
Rightward Shift ◽  
Length Dependence ◽  
Force Depression ◽  
In Series

Relative force depression associated with muscle fatigue is reported to be greater when assessed at short vs. long muscle lengths. This appears to be due to a rightward shift in the force-length relationship. This rightward shift may be caused by stretch of in-series structures, making sarcomere lengths shorter at any given muscle length. Submaximal force-length relationships (twitch, double pulse, 50 Hz) were evaluated before and after repetitive contractions (50 Hz, 300 ms, 1/s) in an in situ preparation of the rat medial gastrocnemius muscle. In some experiments, fascicle lengths were measured with sonomicrometry. Before repetitive stimulation, fascicle lengths were 11.3 ± 0.8, 12.8 ± 0.9, and 14.4 ± 1.2 mm at lengths corresponding to −3.6, 0, and 3.6 mm where 0 is a reference length that corresponds with maximal active force for double-pulse stimulation. After repetitive stimulation, there was no change in fascicle lengths; these lengths were 11.4 ± 0.8, 12.6 ± 0.9, and 14.2 ± 1.2 mm. The length dependence of fatigue was, therefore, not due to a stretch of in-series structures. Interestingly, the rightward shift that was evident when active force was calculated in the traditional way (subtraction of the passive force measured before contraction) was not seen when active force was calculated by subtracting the passive force that was associated with the fascicle length reached at the peak of the contraction. This calculation is based on the assumption that passive force decreases as the fascicles shorten during a fixed-end contraction. This alternative calculation revealed similar postfatigue absolute active force depression at all lengths. In relative terms, a length dependence of fatigue was still evident, but this was greatly diminished compared with that observed when active force was calculated with the traditional method.

Effects of acidosis on Ca2+sensitivity of contractile elements in intact ferret myocardium

1998 ◽  
Vol 274 (1) ◽  
pp. H147-H154 ◽  
Author(s):  
Kimiaki Komukai ◽  
Tetsuya Ishikawa ◽  
Satoshi Kurihara
Keyword(s):  
Muscle Length ◽  
Length Change ◽  
Troponin C ◽  
Tetanic Contraction ◽  
Twitch Contraction ◽  
Intracellular Ca ◽  
The Right ◽  
The Hill ◽  
The Relationship ◽  
Stimulation Of

We investigated the effects of acidosis on the intracellular Ca2+ concentration ([Ca2+]i) and contractile properties of intact mammalian cardiac muscle during tetanic and twitch contractions. Aequorin was injected into ferret papillary muscles, and the [Ca2+]iand tension were simultaneously measured. Acidosis was attained by increasing the CO2 concentration in the bicarbonate (20 mM)-buffered Tyrode solution from 5% (pH 7.35, control) to 15% (pH 6.89, acidosis). Tetanic contraction was produced by repetitive stimulation of the preparation following treatment with 5 μM ryanodine. The relationship between [Ca2+]iand tension was measured 6 s after the onset of the stimulation and was fitted using the Hill equation. Acidosis decreased the maximal tension to 81 ± 2% of the control and shifted the [Ca2+]i-tension relationship to the right by 0.18 ± 0.01 pCa units. During twitch contraction, a quick shortening of muscle length from the length at which developed tension became maximal ( L max) to 92% L maxproduced a transient change in the [Ca2+]i(extra Ca2+). The magnitude of the extra Ca2+ was dependent on the [Ca2+]iimmediately before the length change, suggesting that the extra Ca2+ is related to the amount of troponin-Ca complex. Acidosis decreased the normalized extra Ca2+ to [Ca2+]iimmediately before the length change, which indicates that the amount of Ca2+ bound to troponin C is less when [Ca2+]iis the same as in the control. The decrease in the Ca2+ binding to troponin C explains the decrease in tetanic and twitch contraction, and mechanical stress applied to the preparation induced less [Ca2+]ichange in acidosis.

Length-dependent potentiation and myosin light chain phosphorylation in rat gastrocnemius muscle

1997 ◽  
Vol 273 (1) ◽  
pp. C198-C204 ◽  
Author(s):  
D. E. Rassier ◽  
L. A. Tubman ◽  
B. R. MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Gastrocnemius Muscle ◽  
Average Rate ◽  
Muscle Length ◽  
Repetitive Stimulation ◽  
Mammalian Skeletal Muscle ◽  
Optimal Length ◽  
Regulatory Light Chains ◽  
Dependent Change

Changes in muscle length affect the degree of staircase potentiation in skeletal muscle, but the mechanism by which this occurs is unknown. In this study, we tested the hypothesis that length-dependent change in staircase is modulated by phosphorylation of the myosin regulatory light chains (RLC), since this is believed to be the main mechanism of potentiation. In situ isometric contractile responses of rat gastrocnemius muscle during 10 s of repetitive stimulation at 10 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. The degree of enhancement of developed tension during 10 s of repetitive stimulation was observed to be length dependent, with increases of 118.5 +/- 7.8, 63.1 +/- 3.9, and 45.6 +/- 4.1% (means +/- SE) at Lo - 10%, Lo, and Lo + 10%, respectively. Staircase was accompanied by increases in the average rate of force development of 105.6 +/- 7.7, 55.6 +/- 4.1, and 37.2 +/- 4.4% for Lo - 10%, Lo, and Lo + 10%, respectively. RLC phosphorylation after 10 s of 10-Hz stimulation was higher than under resting conditions but not different among Lo - 10% (40 +/- 3.5%), Lo (35 +/- 3.5%), and Lo + 10% (41 +/- 3.5%). This study shows that there is a length dependence of staircase potentiation in mammalian skeletal muscle that may not be directly modulated by RLC phosphorylation. Interaction of RLC phosphorylation with length-dependent changes in Ca2+ release and intermyofilament spacing may explain these observations.

Caffeine and length dependence of staircase potentiation in skeletal muscle

1998 ◽  
Vol 76 (10-11) ◽  
pp. 975-982 ◽  
Author(s):  
Dilson E Rassier ◽  
L Aaron Tubman ◽  
Brian R MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Muscle Length ◽  
Negative Slope ◽  
Muscle Twitch ◽  
Optimal Length ◽  
Length Dependence ◽  
Before And After ◽  
Isometric Twitch ◽  
The Relationship

Skeletal muscle sensitivity to Ca2+ is greater at long lengths, and this results in an optimal length for twitch contractions that is longer than optimal length for tetanic contractions. Caffeine abolishes this length dependence of Ca2+ sensitivity. Muscle length (ML) also affects the degree of staircase potentiation. Since staircase potentiation is apparently caused by an increased Ca2+ sensitivity of the myofilaments, we tested the hypothesis that caffeine depresses the length dependence of staircase potentiation. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 10 s of 10-Hz stimulation were analyzed at seven different lengths to evaluate the length dependence of staircase potentiation. In the absence of caffeine, length dependence of Ca2+ sensitivity was observed, and the degree of potentiation after 10-Hz stimulation showed a linear decrease with increased length (DT = 1.47 - 0.05ML, r2 = 0.95, where DT is developed tension). Length dependence of Ca2+ sensitivity was decreased by caffeine when caffeine was administered in amounts estimated to result in 0.5 and 0.75 mM concentrations. Furthermore, the negative slope of the relationship between staircase potentiation and muscle length was diminished at the lower caffeine dose, and the slope was not different from zero after the higher dose (DT = 1.53 - 0.009ML, r2 = 0.43). Our study shows that length dependence of Ca2+ sensitivity in intact skeletal muscle is diminished by caffeine. Caffeine also suppressed the length dependence of staircase potentiation, suggesting that the mechanism of this length dependence may be closely related to the mechanism for length dependence of Ca2+ sensitivity.Key words: skeletal muscle, twitch contraction, Ca2+ sensitivity, muscle length, staircase.

Fluorescent properties of rat cardiac trabeculae microinjected with fura-2 salt

1993 ◽  
Vol 264 (4) ◽  
pp. H1098-H1110 ◽  
Author(s):  
P. H. Backx ◽  
H. E. Ter Keurs
Keyword(s):  
Time Course ◽  
Temporal Relationship ◽  
Sarcomere Length ◽  
Muscle Length ◽  
Papillary Muscles ◽  
Fluorescent Properties ◽  
Acetoxymethyl Ester ◽  
Fura 2 ◽  
Relaxation Period ◽  
The Relationship

We have measured force, sarcomere length, and Ca2+ during twitches in rat cardiac trabeculae. To avoid the difficulties associated with fura-2/acetoxymethyl ester (AM), fura-2 salt was iontophoretically microinjected into the preparation using a single impalement site; this is possible because fura-2 diffuses through the gap junctions between cells. By use of this method, the estimated peak of the [Ca2+] transient during a twitch was not statistically different at different sarcomere lengths: 875 +/- 92 nM at a sarcomere length of 2.15 microns vs. 905 +/- 67 nM at a sarcomere length of 1.65 microns (means +/- SD, n = 10). When trabeculae were loaded using fura-2/AM, the estimated peak of the [Ca2+] transient at a sarcomere length of 2.15 microns was 540 +/- 180 nM (means +/- SD, n = 5). The time course of the Ca2+ transients at different sarcomere lengths is qualitatively similar, but small systematic differences were observed during the relaxation period. On the other hand, the duration of twitch force increases dramatically as the muscle length is increased. As a result, when the trabeculae were held at short muscle lengths, the temporal relationship between force and the Ca2+ transient resembled the relationship between cell shortening and the Ca2+ transient measured in isolated myocytes. At longer lengths the temporal relationship between force and the Ca2+ transient more closely resembles that obtained in papillary muscles using aequorin.

Length dependence of staircase potentiation: interactions with caffeine and dantrolene sodium

2000 ◽  
Vol 78 (4) ◽  
pp. 350-357 ◽  
Author(s):  
Dilson E Rassier ◽  
Brian R MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Gastrocnemius Muscle ◽  
Repetitive Stimulation ◽  
Mammalian Skeletal Muscle ◽  
Optimal Length ◽  
Dantrolene Sodium ◽  
Length Dependence ◽  
Before And After ◽  
Isometric Twitch

In skeletal muscle, there is a length dependence of staircase potentiation for which the mechanism is unclear. In this study we tested the hypothesis that abolition of this length dependence by caffeine is effected by a mechanism independent of enhanced Ca2+ release. To test this hypothesis we have used caffeine, which abolishes length dependence of potentiation, and dantrolene sodium, which inhibits Ca2+ release. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 20 s of repetitive stimulation at 5 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. Potentiation was observed to be length dependent, with an increase in developed tension (DT) of 78 ± 12, 51 ± 5, and 34 ± 9% (mean ± SEM), at Lo - 10%, Lo, and Lo + 10%, respectively. Caffeine diminished the length dependence of activation and suppressed the length dependence of staircase potentiation, giving increases in DT of 65±13, 53 ± 11, and 45 ± 12% for Lo - 10%, Lo, and Lo + 10%, respectively. Dantrolene administered after caffeine did not reverse this effect. Dantrolene alone depressed the potentiation response, but did not affect the length dependence of staircase potentiation, with increases in DT of 58 ± 17, 26 ± 8, and 18 ± 7%, respectively. This study confirms that there is a length dependence of staircase potentiation in mammalian skeletal muscle which is suppressed by caffeine. Since dantrolene did not alter this suppression of the length dependence of potentiation by caffeine, it is apparently not directly modulated by Ca2+ availability in the myoplasm.

scholarly journals Influence of muscle length on work from trabecular muscle of frog atrium and ventricle.

1995 ◽  
Vol 198 (10) ◽  
pp. 2221-2227 ◽  
Author(s):  
D A Syme ◽  
R K Josephson
Keyword(s):  
Isometric Force ◽  
Muscle Length ◽  
Work Capacity ◽  
Linear Increase ◽  
Ventricular Muscle ◽  
Work Output ◽  
Loop Technique ◽  
Work Done ◽  
The Relationship ◽  
Work Loop

The work capacity of segments of atrial and ventricular muscle from the frog Rana pipiens was measured as a function of muscle length using the work loop technique. Both the work done during shortening and the work required to re-lengthen the muscle after shortening increased with muscle length. Net work increased with length up to a maximum, beyond which work declined. The optimum sarcomere length for work output was 2.5-2.6 microns for both atrial and ventricular muscle. Isometric force increased with muscle length to lengths well beyond the optimum for work output. Thus, the decline in work at long lengths is not simply a consequence of a reduction in the capacity of heart muscle to generate force. It is proposed that it is the non-linear increase in work required to re-lengthen muscle with increasing muscle length which limits net work output and leads to a maximum in the relationship between net work and muscle length. Extension of the results from muscle strips to intact hearts suggests that the work required to fill the ventricle exceeds that available from atrial muscle at all but rather short ventricular muscle lengths.

Transient responses and continuous behavior of active smooth muscle during controlled stretches

1982 ◽  
Vol 242 (3) ◽  
pp. C146-C158 ◽  
Author(s):  
R. A. Meiss
Keyword(s):  
Steady State ◽  
Smooth Muscles ◽  
Muscle Length ◽  
Initial Slope ◽  
Stretch Rate ◽  
Rate Dependent ◽  
Upward Slope ◽  
Length Changes ◽  
State Force ◽  
The Relationship

Controlled length changes were imposed on mesotubarium superius and ovarian ligament smooth muscles from the reproductive tracts of female rabbits in constant estrus. Stretches of up to 35% of the muscle length were applied during isometric contraction, relaxation, and steady-state force levels. Force was continuously monitored and was plotted as a function of length. During constant velocity stretches there was an initial steep rise in force, a rapid downward deviation from the initial slope, and a long region with a constant upward slope. Stretches made during contraction showed smaller initial rises in force and steeper linear portions than did identical comparison stretches made during relaxation. The value of the slope was independent of the prior developed force, but it did depend on whether the muscle was contracting or relaxing. During contraction and steady-state force levels, the slope was independent of the stretch rate, but it was strongly rate dependent during relaxation. Changes in the stretch rate during stretch caused associated changes in muscle force; the relationship was curvilinear and was exaggerated during relaxation. The findings are placed in the context of a sliding-filament--cross-bridge hypothesis.

Sign in / Sign up

Export Citation Format

Share Document