Abstract
The ultrastructure of rabbit skeletal muscle was studied following glycerolation and staining with pyroantimonate. Electron-dense deposits were observed within the residual sarcoplasmic reticulum and associated with myofilaments. These dense granules were removed by chelation with EGTA and granules reappeared at these same sites upon the addition of calcium ions to the incubation medium. Specific inter- and intra-myofibrillar binding sites were thus confirmed. Myofilament binding sites were found to be a function of sarcomere length, since the granule distribution was different when shorter sarcomeres were compared to longer sarcomeres. It is proposed that calcium bound to myofilaments plays an essential role in contraction coupling and relaxation.
Résumé
L'ultrastructure du muscle squelettique de lapin est étudiée après traitement au glycérol et colgoration au pyroantimonate. Des dépôts denses aux électrons sont observés dans le reticulum sarcoplasmique restant. Ils sont associés aux myofilaments. Ces granules denses sont éliminés par chélation à l'EDTA et ces granules réapparaissent aux mêmes localisations après adjonction d'ions calcium au milieu d'incubation. L'existence de sites de liaisons spécifiques inter et intramyofibrillaires est ainsi confirmée. Les sites de liaison des myofilaments sont en rapport avec la longueur du sarcomère, étant donné que la localisation des granules est différente lorsque des sarcomères plus courts sont comparés à des sarcomères plus longs. Il semble que le calcium lié aux myofilaments joue un rôle essentiel au cours de la coordination et de la phase de repos de la contraction musculaire.
Zusammenfassung
Die Ultrastruktur des Skelettmuskels von Kaninchen wurde durch Einlegen in Glycerin und Färbung mit Pyroantimonat untersucht. Es wurden im residualen Sarkoplasma-Reticulum elektronendichte Ablagerungen beobachtet und mit Myofilamenten in Zusammenhang gebracht. Diese dichten Granula verschwanden durch Chelation mit EGTA, und neue Granula erschienen an denselben Stellen, wenn dem Inkubationsmedium Calciumionen beigegeben wurden. Auf diese Weise wurde das Auftreten spezifischer inter- und intramyofibrillärer Bindungsstellen bestätigt. Es wurde festgestellt, daß die Myofilament-Bindungsstellen von der Länge der Sarkomeren abhingen, denn die Verteilung der Granula war verschieden, wenn kürzere Sarkomeren mit längeren verglichen wurden. Es wird vorgeschlagen, daß das an Myofilamente gebundene Calcium eine wesentliche Rolle in der Kontraktion, der Verbinding und der Relaxation spielt.
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This work was supported in part by grants from the National Institutes of Health, Numbers DE0024-04, AM13799-01, and grant from the Atomic Energy Commission, AT-(40-1)-4056.
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Davis, W.L., Matthews, J.L. & Martin, J.H. An electron microscopic study of myofilament calcium binding sites in native, EGTA-chelated and calcium reloaded glycerolated mammalian skeletal muscle. Calc. Tis Res. 14, 139–152 (1974). https://doi.org/10.1007/BF02060290
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DOI: https://doi.org/10.1007/BF02060290