Dynamic relations among length, tension, and intracellular  Ca2+ in activated ferret papillary muscles

To study the effects of mechanical constraints on the Ca2+ affinity of cardiac troponin C, we analyzed the tension and aequorin light (AL) responses to sinusoidal length changes (5–10% of the initial muscle length) in aequorin-injected, tetanized cardiac muscles. The amplitude of the quasi-sinusoidal tension and AL responses decreased with increasing length-perturbation frequency from 0.5 to 1 Hz at 24°C and from 1 to 3 Hz at 30°C. The increase in AL corresponded well to the decrease in tension; likewise, the decrease in AL to the increase in tension and the tension response lagged behind the length change. A further increase in frequency (>1 Hz at 24°C and >3 Hz at 30°C) markedly increased the amplitude of the tension responses but decreased the amplitude of the AL responses. The increase in AL lagged behind the decrease in tension; likewise, the decrease in AL lagged behind the increase in tension, and the tension response led the length change. From previous mechanistic interpretations of the frequency dependence of the amplitude of tension response, we argue that the Ca2+affinity of cardiac troponin C changes in parallel with the active tension (i.e., the number of active cross bridges) but not with the passive tension produced by the length perturbation-induced cross-bridge strain.

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Transient tension responses of heart muscle in Ba2+ contracture to step length changes

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1980.238.3.h340 ◽

1980 ◽

Vol 238 (3) ◽

pp. H340-H347 ◽

Cited By ~ 2

Author(s):

Y. Saeki ◽

K. Sagawa ◽

H. Suga

Keyword(s):

Heart Muscle ◽

Muscle Length ◽

Length Change ◽

Step Length ◽

Second Phase ◽

Tension Response ◽

Third Phase ◽

Different Temperatures ◽

Length Changes ◽

Stretch Response

To characterize mechanical properties of activated heart muscle, kitten papillary muscles in Ba2+ contracture were stretched or released stepwise, and the transient tension responses were analyzed. Various amplitudes of step length change (0.1-1.0% of Lmax) were tested from different initial lengths and at different temperatures. The tension response to either stretch or release showed four different phases, which were nearly symmetric when the input length change was 0.1% of Lmax. When the length changes was 1%, the second phase of stretch response became shorter, whereas that of release became longer. The third phase of stretch response was prolonged, whereas that of release response became obscure. The peak tension (F1) in the first phase was linearly related to the amplitude, whereas those in the second and third phase were not. Increasing temperature markedly decreased F1 and shortened the second and third phase independently of initial muscle length. These results were consistent with those properties of heart muscle in Ba2+ contracture previously characterized with sinusoidal length changes.

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Structural basis for the in situ Ca2+ sensitization of cardiac troponin C by positive feedback from force-generating myosin cross-bridges

Archives of Biochemistry and Biophysics ◽

10.1016/j.abb.2013.07.013 ◽

2013 ◽

Vol 537 (2) ◽

pp. 198-209 ◽

Cited By ~ 17

Author(s):

Daniel C. Rieck ◽

King-Lun Li ◽

Yexin Ouyang ◽

R. John Solaro ◽

Wen-Ji Dong

Keyword(s):

Positive Feedback ◽

Cardiac Troponin ◽

Troponin C ◽

Structural Basis ◽

Cardiac Troponin C ◽

Cross Bridges

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Effect of length and cross-bridge attachment on Ca2+ binding to cardiac troponin C

AJP Cell Physiology ◽

10.1152/ajpcell.1987.253.1.c90 ◽

1987 ◽

Vol 253 (1) ◽

pp. C90-C96 ◽

Cited By ~ 110

Author(s):

P. A. Hofmann ◽

F. Fuchs

Keyword(s):

Cardiac Muscle ◽

Cardiac Troponin ◽

Sarcomere Length ◽

Troponin C ◽

Saturation Curve ◽

Cross Bridge ◽

Cardiac Troponin C ◽

Length Dependence ◽

Length Relationship ◽

Cross Bridges

The sensitivity of skinned cardiac muscle bundles to Ca2+ is a function of sarcomere length. Ca2+ sensitivity is increased as fiber length is extended along the ascending limb of the force-length curve and it has been suggested that this phenomenon makes a major contribution to the steep force-length relationship that exists in living cardiac muscle. To gain greater insight into the mechanism behind the length dependence of Ca2+ sensitivity isotopic measurements of Ca2+ binding to detergent-extracted bovine, ventricular muscle bundles were made under conditions in which troponin C was the only major Ca2+ binding species. Experiments were designed to determine whether 1) Ca2+-troponin C affinity varies in the sarcomere length range corresponding to the ascending limb of the force-length curve, and 2) Ca2+ binding correlates with length per se or with changes in the number of length-dependent cross-bridge attachments. Measurements were made of Ca2+ binding in the rigor and relaxed states. The latter state was produced by suppressing actin-myosin interaction with the phosphate analogue, sodium vanadate. After vanadate treatment it is possible to obtain a complete Ca2+ saturation curve in the presence of physiological MgATP concentrations and at constant sarcomere length. The results show that the binding of Ca2+ to the regulatory site of cardiac troponin C is length dependent but this length dependence is actually a dependence on the number of attached cross bridges.

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