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Resting Sarcomere Length-Tension Relation in Living Frog Heart

Resting Sarcomere Length-Tension Relation in Living Frog Heart,10.1085/jgp.64.3.343,Journal of General Physiology,SAUL WINEGRAD

Resting Sarcomere Length-Tension Relation in Living Frog Heart   (Citations: 9)
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The sarcomere pattern and tension of isolated resting frog atrial trabeculae were continuously monitored. In the absence of any resting tension the sarcomere lengths varied with the diameter of the trabeculae. In over 75 % of the trabeculae the value exceeded 2.05 Am, the estimated in vivo length of the thin filaments, and it was never less than 1.89 ,um. When the trabeculae were stretched the increase in length of the central undamaged portion could be completely accounted for by an increase in sarcomere length. The width of the A band was constant only at sarcomere lengths between 2.3 and 2.6 am; it decreased at smaller and increased at larger sarcomere lengths. A group of spontaneously active cells stretched the sarcomeres in cells in series to longer lengths than could be produced by passive tension applied to the ends of the trabeculae, but they did not influence the sarcomeres of adjacent cells. It is pro- posed that the connective tissue is a major factor in determining sarcomere length and that there are interactions between thick and thin filaments in rest- ing muscles. Although the relation between the resting volume of a heart and the tension that it develops during systole was described over 50 years ago by Frank (1895) and by Starling (1918), the basis is still unknown. The most obvious length- dependent contractile function to which this relation may be attributed evolves from the sliding hypothesis of contraction of skeletal muscle and de- pends on the amount of overlap of thick and thin filaments. Force generators are believed to be uniformly distributed along the length of the thick filament except for its central 0.10-0.15 pm, but to be active they must be overlapped by thin filaments. The number of force generators available during a given contraction is, therefore, length dependent and, as has been shown by Gordon et al. (1966), can be accurately estimated by the sarcomere length. If the basis of the length-tension curve in cardiac muscle is the number of force generators that can interact with the thin filaments, the lengths of sarcomeres in cardiac tissue at different positions on its length-tension curve must have quite spe- cific values. There have been several attempts to evaluate this possibility by determining
Journal: Journal of General Physiology - J GEN PHYSIOL , vol. 64, no. 3, pp. 343-355, 1974
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    • ...Intact, multicellular strips of heart muscle consist of a population of contractile cells having an unknown distribution of orientation and force generation, intimately surrounded by a connective tissue matrix (Gay and Johnson 1967; Winegrad 1974)...

    Leslie Tung. An ultrasensitive transducer for measurement of isometric contractile ...

    • ...In contrast, both Winegrad (1974) and Matsubara and Maruyama (1977) found that the resting tension increased significantly over the sarcomere length range of 2.0-2.6 /xm in small bundles of frog atrial tissue...
    • ...It generally has been thought that the relatively high resting tension characteristic of cardiac tissue resides in structures (collagen, elastin) external to the individual cardiac cells (Gay and Johnson, 1967; Winegrad, 1974)...
    • ...Somewhat smaller values have been reported for small bundles of frog atrial tissue (Winegrad, 1974), where the resting stress was on the order of 40 g/cm2 (3.9 mN/mm2) at a sarcomere length of 2.2 /xm and 300 g/cm2 (29 mN/ mm2) at a sarcomere length of 2.6 fim...
    • ...It previously has been suggested by some investigators that individual cardiac cells are responsible for very little of the stiffness characteristic of intact cardiac tissue (Gay and Johnson, 1967; Winegrad, 1974), but these suggestions were based on indirect evidence...
    • ...The data presented in this paper directly support the conclusion that the stiffness of resting intact frog atrial cardiac preparations resides primarily in structures external to the individual cardiac cell, since the resting stress in the isolated frog atrial cell at sarcomere lengths of 2.2-2.6 is 8- to 30fold less than values reported for intact frog atrial tissue (Winegrad, 1974)...

    MERRILL TARRet al. Sarcomere Length-Resting Tension Relation in Single Frog Atrial Cardia...

    • ...4a and 5) are similar to those obtained previously with cardiac muscle and whole heart preparations (Spiro and Sonnenblick, 1964; Spotnitz et al., 1966; Winegrad, 1974)...
    • ...The atrial cells studied by Tarr et al., were found to be more compliant than intact frog atrial trabeculae studied by Winegrad (1974)...
    • ...At any rate, the length-tension curve obtained by Tarr et al. is shifted considerably to the right, compared with those obtained with frog atrial trabeculae (Winegrad, 1974)...

    J Orensteinet al. Passive stiffness of isolated cardiac and skeletal myocytes in the ham...

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