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K R PORTER

Publications and source records attributed to K R PORTER.

At least 37 records · Page 2Linked to original sources
PubMed1957

Studies on the endoplasmic reticulum. III. Its form and distribution in striated muscle cells.

Several types of striated muscle have been examined by the technics of electron microscopy and the findings in myotome fibers of Amblystoma larvae, the sartorius, and cardiac muscle of the rat are reported on in some detail. Particular attention has been given to structural components of the interfibrillar sarcoplasm and most especially to a finely divided, vacuolar system known as the sarcoplasmic reticulum. This consists of membrane-limited vesicles, tubules, and cisternae associated in a continuous reticular structure which forms lace-like sleeves around the myofibrils. It shows a definable organization which repeats with each sarcomere of the fiber so that the entire system is segmented in phase with the striations of the associated myofibrils. Details of these repetitive patterns are presented diagrammatically in Text-figs. 1, 2, and 3 on pages 279, 283, and 288 respectively. The system is continuous across the fiber at the H band level and largely discontinuous longitudinally because of interruptions in the structure at the I and Z band levels. The structure of the system relates it to the endoplasmic reticulum of other cell types. The precise morphological relation of the reticulum to the myofibrils, with specializations opposite the different bands, prompts the supposition that the system is functionally important in muscle contraction. In this regard it is proposed that the membrane limiting the system is polarized like the sarcolemma and that the corresponding potential difference is utilized in the intracellular distribution of the excitatory impulse.

Animals↗
PubMed1956

The sarcoplasmic reticulum in muscle cells of Amblystoma larvae.

Electron microscopy of thin sections of muscle fibers in myotomes of Amblystoma larvae has revealed the presence of a complex, membrane-limited system of canaliculi and vesicles which form a lace-like reticulum around and among the myofibrils. This seems to correspond to the sarcoplasmic reticulum of the earlier light microscopists and the endoplasmic reticulum of other cell types. The elements constituting the reticulum are disposed in a pattern which bears a constant relation to the bands of the adjacent myofibrils and is therefore repeated in each sarcomere. At the H band the system is transversely continuous but not so at other levels. Longitudinally continuity is interrupted at the Z bands where large vesicles belonging to adjacent sarcomere segments of the system face off on opposite sides of the band. The opposing faces of these vesicles are flat and separated by a space of more or less constant width, in which are located small, finger-shaped vesicles. In view of these and other close structural relationships with the myofibrils it seems appropriate to assign to the system a role in the conduction of the excitatory impulse.

Ambystoma↗
PubMed1955

The fine structure of cortical components of Paramecium multimicronucleatum.

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 approximately 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.

Animals↗
PubMed1955

Observations on the fine structure of the macronucleus of Tokophrya infusionum.

The macronucleus in Tokophrya infusionum is composed of numerous Feulgen-positive chromatin bodies (about 0.5 micro in diameter) which appear in thin sections as a dense spongework, homogeneous throughout. The same appearance characterizes metaphase chromosomes of higher forms. Some chromatin bodies of the macronucleus were found to possess a highly organized structure in certain old organisms. This structure appears in cross-sections as a honeycomb and in longitudinal sections as parallel lines about 120 A in diameter evenly spaced (about 230 A). As far as is known this is the first time a regular structure has been found in bodies of chromosomal character at the dimensional level presently explored by electron microscopy. The demonstration that OsO(4) can preserve order in chromatin material is another significant aspect of these findings.

Cell Nucleus↗
PubMed1954

Studies on the endoplasmic reticulum. I. Its identification in cells in situ.

A series of representative cell types including avian fibroblasts, and macrophages; rabbit mesothelia, endothelia, and nephron epithelia; and rat glandular epithelia (parotid) were studied comparatively in vitro and in situ with the electron microscope. Cells in vitro were examined in whole mounts and in sections whereas cells in situ were observed exclusively in sections. It was found that an endoplasmic reticulum similar to that previously described in cultured material is present in situ in all cell types examined. Modifications in its appearance introduced by the sectioning technique were discussed and explained. The observations showed in addition that the endoplasmic reticulum is a network of cavities which may enlarge into relatively vast, flattened vesicles here described as cisternae.

Animals↗
PubMed1953

Observations on a submicroscopic basophilic component of cytoplasm.

The cytoplasmic ground substance of animal tissue cells grown in vitro has been found by electron microscopy to contain, as a part of its submicroscopic structure, a complex reticulum of strands, to be referred to as the endoplasmic reticulum. It has been found in all types of cells extensively studied. The components of this reticular system vary considerably in size and form, apparently in some relation to physiological changes in the cell. Thus in one cell of a culture colony it may be finely divided into strands or canaliculi, 50 to 100 mmicro in diameter, whereas in an adjacent cell of the same type the components of the reticulum may be relatively coarse, 600 mmicro in diameter, and vesiculated. The membrane, which can be shown to limit the system and separate it from the rest of the ground substance, is similar in thickness to the plasma membrane surrounding the cell. Photomicrographs of living cells taken by phase contrast and dark field microscopy define a structure of similar form and indicate that the reticulum of the electron microscope image has its equivalent in the living unit. Where its component units are sufficiently large, a structure of identical form can be resolved by light microscopy in cells stained with hematoxylin or with toluidine blue. This indicated that the endoplasmic reticulum is to be identified with the basophilic or chromophilic component (the ergastoplasm) of the cytoplasm and that such properties of this component as have been determined by cytochemical methods, such as a high RNA content, may be assigned to this "submicroscopic" system.

Animals↗