Phase and Electron Microscope Studies of the Interrelationship of Cytochondria and Myofibrils in Pigeon Breast Muscle

145

The electron microscope was used to study the structure and three dimensional relationships of the components of the body cortex in thin sections of Paramecium multimicronucleatum. Micrographs of sections show that the cortex is covered externally by two closely apposed membranes (together ∼250 A thick) constituting the pellicle. Beneath the pellicle the surface of the animal is molded into ridges that form a polygonal ridgework with depressed centers. It is these ridges that give the surface of the organism its characteristic configuration and correspond to the outer fibrillar system of the light microscope image. The outer ends of the trichocysts with their hood-shaped caps are located in the centers of the anterior and posterior ridges of each polygon. The cilia extend singly from the depressed centers of the surface polygons. Each cilium shows two axial filaments with 9 peripheral and parallel filaments embedded in a matrix and the whole surrouned by a thin ciliary membrane. The 9 peripheral filaments are double and these are evenly spaced in a circle around the central pair. The ciliary membrane is continuous with the outer member of the pellicular membrane, whereas the plasma membrane is continuous with the inner member of the pellicular membrane. At the level of the plasma membrane the proximal end of the cilium is continuous with its tube-shaped basal body or kinetosome. The peripheral filaments of the cilium, together with the material of cortical matrix which tends to condense around them, form the sheath of the basal body. The kinetodesma connecting the ciliary kinetosomes (inner fibrillar system of the light microscopist) is composed of a number of discrete fibrils which overlap in a shingle-like fashion. Each striated kinetosomal fibril originates from a ciliary kinetosome and runs parallel to other kinetosomal fibrils arising from posterior kinetosomes of a particular meridional array. Sections at the level of the ciliary kinetosomes reveal an additional fiber system, the infraciliary lattice system, which is separate and distinct from the kinetodesmal system. This system consists of a fibrous network of irregular polygons and runs roughly parallel to the surface of the animal. Mitochondria have a fine structure similar in general features to that described for a number of mammalian cell types, but different in certain details. The structures corresponding to cristae mitochondriales appear as finger-like projections or microvilli extending into the matrix of the organelle from the inner membrane of the paired mitochondrial membrane. The cortical cytoplasm contains also a particulate component and a system of vesicles respectively comparable to the nucleoprotein particles and to the endoplasmic reticulum described in various metazoan cell types. An accessory kinetosome has been observed in oblique sections of a number of non-dividing specimens slightly removed from the ciliary kinetosome and on the same meridional line as the cilia and trichocysts. Its position corresponds to the location of the kinetosome of the newly formed cilium in animals selected as being in the approaching fission stage of the life cycle.

Section: Discussionmentioning

confidence: 99%

The Fine Structure of Cortical Components of Paramecium Multimicronucleatum

Sedar

Porter

1955

145

“…The shadow or projection of this is broad and grades off gradually in density to that of the surrounding sarcoplasmic matrix. Images such as this have led Harman and coworkers to describe mitochondria as gelatinous bodies devoid of membranes (21,22). At one end of the mitochondrion, below the one marked m, the surface passes at right angles through the section and here a line of characteristic density and doubleness can be seen to limit the organelle.…”

Section: Discussionmentioning

confidence: 99%

“…2 and 3). (See Weinreb and Harman (21) and Harman (22) for a conflicting interpretation.) Lipide inclusions, characterized by a very high density after osmium fixation, are encountered in small numbers and usually in close association with the mitochondria (Fig.…”

Section: Studies On L'~l~ Endoplasmic P~ticulum Himentioning

confidence: 99%

Studies on the Endoplasmic Reticulum

Porter

Palade

1957

722

204

Previous papers in this series (1, 2) as well as numerous other reports on cell fine structure have provided evidence for the existence of a finely divided vacuolar system in the cytoplasm of all animal cells thus far examined except mature erythrocytes. The reticular character of the system and its exclusion from the thin cortical layer (ectoplasm) of the cytoplasm, as first observed in cultured cells (3,4), account for the name "endoplasmic reticulum." More recently, in electron microscope studies of thin sections, the term has been applied to small tubular or vesicular elements of the cytoplasm that are limited by a single continuous membrane and have a homogeneous, structurefree content. In the majority of cells, such elements make up a system that is continuous and reticular in form. By its presence the cytoplasm is divided into two phases: (a) a constantly continuous phase, the cytoplasmic matrix, containing such resolvable components as ribonucleoprotein (RNP) particles and fibrous elements of several kinds, and (b) the inner phase of the membranelimited reticulum, in general also continuous, but certainly discontinuous at times, and showing usually no resolvable elements. In some cells the system is abundantly represented; in others sparsely so. Its form, volume, and distribution tend to be characteristic for all cells of a particular type so that it becomes a feature of cellular differentiation. The system has also been observed to show local differentiations (2, 6) and to develop special associations with other components (e.g., the RNP particles (5) and the nucleus (6)). Since it is reasonable to look to them for clues to the functions of the system, these latter associations seem especially significant. Some attention is therefore being given, in this and subsequent studies, to their occurrence, form, and behavior.There are various indications to be found in published accounts of the structure of striated muscle that an equivalent of the endoplasmic reticulum is present in this as in Other types of cells, and that it may show a pattern of distribution relative to the myofibrils. For example, Bennett and Porter (7), in a report on the fine structure of striated muscle of the domestic fowl, directed attention to an interfibrillar component--in some instances vesicular--localized opposite the Z or N bands of the myofibrils. Similar elements were later depicted 269 J, BIOPHYSXC, ~tr~D Bloc~tz~, Cx-roL., 1957, Vol. 3, No. 2 on May 10, 2018 jcb.rupress.org Downloaded from http://doi.org/10. 1083/jcb.3.2.269 Published Online: 25 March, 1957 270 STUDIES ON T/-~ ENDOPLASMIC RETICULUM. HI in the sarcoplasm of insect muscle (8) and more clearly in muscle of Amblystoma larvae (9, 10) and the gracilis muscle of the mouse (11).These miscellaneous and preliminary observations have failed, however, to give more than a suggestion of the pattern the system adopts with respect to the myofibrils. In this regard, in fact, these recent observations are perhaps not so useful as older, somewhat neglected light microscop...

“…This assumption appears to be made also by Weinreb and Harman (19) in interpreting their electron micrographs of pigeon breast muscle, in that the absence of continuous lines around the mitochondria seen in their preparations is taken as morphological evidence for the absence of a limiting membrane. On the basis of their observations on this material, these investigators have proposed a "folded ribbon" theory for the internal structure of mitochondria.…”

Section: Discussionmentioning

confidence: 88%

The Structure of Pigeon Breast Muscle Mitochondria

Howatson

1956

The structure of pigeon breast muscle mitochondria was studied both in whole muscle tissue and in mitochondrial fractions separated by differential centrifugation. No evidence was found to indicate that the mitochondria of pigeon breast muscle differ in any fundamental way from those of other tissues. In particular the absence of an enveloping membrane, claimed in recent reports, was not confirmed. The structure of the lipide bodies present in muscle has been described, and compared with that of similar bodies in other tissues.