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THE ORGANIZATION OF THE SARCOPLASMIC RETICULUM AND T SYSTEM IN THE FEMORAL MUSCLE OF THE HOUSEFLY, MUSCA DOMESTICA

Authors
Journal
The Journal of Cell Biology
0021-9525
Publisher
The Rockefeller University Press
Publication Date
Keywords
  • Brief Notes
  • Article
Disciplines
  • Chemistry

Abstract

BRIEF NOTES THE ORGANIZATION OF THE SARCOPLASMIC RETICULUM AND T SYSTEM IN THE FEMORAL MUSCLE OF THE HOUSEFLY, MUSCA DOMESTICA IVONNE PASQUALI-RONCHETTI. From the Institute of General Pathology, University of Modena, Modena, Italy 41100 INTRODUCTION The role of the T system in the conduction of the stimulus from the sarcolemma inward to the contractile material has been increasingly apparent since the original electron microscopic works by Bennett and Porter (2) and Andersson-Cedergren (1) and the outstanding experiments by Huxley and coworkers (7) on the effects of local stimula- tion. At present, it is well established that in all muscles so far studied the T system originates from invaginations of the sarcolemmal membrane, thus providing a continuous structural basis for the transmission of the stimulus to the contractile material (4, 8, 10, 16, 17). In higher animals (amphibians, birds, and mammals), the T system makes close contact, within the muscle cell, with two cisternal enlarge- ments of the sarcoplasmic reticulum (SR): the resulting structure (triad unit) is thought to be the basis for the electrochemical coupling phenom- ena (8, 10). Triadic structures have been shown to be present also in the muscle fibers of lower animals (12, 14); however, either more complex (pentadic) or apparently simpler (dyadic) structural relations between the T system and the SR membranes have also been reported (3-6, 11, 12, 16). In the case of the dyads, which are by far the alternative to the triads most frequently observed, the sarco- plasmic reticulum forms a continuous sheet onto the surface of the myofibril, and the T system runs alongside the cisternae of the sarcoplasmic reticulum (18); hence the dyadic appearance of the whole structure. However, little attention has been paid to the problem of the very precise tridimensional organization of the dyads, and still poorly understood are the spatial relationships between the membranes of the two systems (3, 15). In this paper, a trid

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