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Biomedical subjects

K R Porter

Publications and source records attributed to K R Porter.

12 recordsLinked to original sources
PubMed1979

Microtrabecular lattice of the cytoplasmic ground substance. Artifact or reality.

The cytoplasmic ground substance of cultured cells prepared for high voltage transmission electron microscopy (glutaraldehyde/osmium fixed, alcohol or acetone dehydrated, critical-point dried) consists of slender (3-6 nm Diam) strands--the microtrabeculae (55)--that form an irregular three-dimensional lattice (the microtrabecular lattice). The microtrabeculae interconnect the membranous and nonmembranous organelles and are confluent with the cortices of the cytoplast. The lattice is found in all portions of the cytoplast of all cultured cells examined. The possibility that the lattice structure is an artifact of specimen preparation has been tested by (a) subjecting whole cultured cells (WI-38, NRK, chick embryo fibroblasts) to various chemical (aldehydes, osmium tetroxide) and nonchemical (freezing) fixation schedules, (b) examination of model systems (erythrocytes, protein solutions), (c) substantiating the relaibility of critical-point drying, and (d) comparing images of whole cells with conventionally prepared (plastic-embedded) cells. The lattice structure is preserved by chemical and nonchemical fixation, though alterations in ultrastructure can occur especially after prolonged exposure to osmium tetroxide. The critical-point method for drying specimens appears to be reliable as is the freeze-drying method. The discrepancies between images of plastic-embedded and sectioned cells, and images of whole, critical-point dried cells appear to be related, in part, to the electron-scattering properties of the embedding resin. The described observations indicate that the microtrabecular lattice seen in electron micrographs closely represents the nonrandom structure of the cytoplasmic ground substance of living cultured cells.

Animals↗
PubMed1977

Observation on the morphological heterogeneity of WI-38 cells.

WI-38 cells of intermediate and late-passage cultures were examined by light microscopy, scanning, conventional transmission and high voltage electron microscopy for evidence of heterogeneity among the cells within a single culture. Two morphologically distinct cell sizes and shapes were noted in all passages, (1) a typical fibroblastic type, and (2) a much larger, non-fusiform type. The larger cells generally had a nucleus that was positioned to one side of the bulk of the cytoplasm. The smaller was consistently fusiform with a centrally placed nucleus. The surfaces of intermediate-passage cells were uniform in showing small microvilli and corticall pits but were otherwise smooth and with out distinctive featues. The late-passage cells, on the other band, were consistent in showing numerous blebs and marginal ruffing. The internal structure of these cells in all passages studied was complicated by many age-related changes. The observations indicate that there is in WI-38 cells a high degree of intraculture heterogeneity. An awareness of this is important in studies which characterize the biochemical properties of this cell strain.

Cell Line↗
PubMed1977

Transformations in the structure of the cytoplasmic ground substance in erythrophores during pigment aggregation and dispersion. I. A study using whole-cell preparations in stereo high voltage electron microscopy.

Pigment migration in cultured erythrophores of the squirrel fish Holocentrus ascensionis, after manipulation with K+, epinephrine, 3',5'-dibutyryl cyclic adenosine monophosphate, theophylline, and caffeine, is essentially identical to that observed in this chromatophore in situ. For such observations, the erythrophores are dissociated from the scales with hyaluronidase and collagenase, and allowed to spread on an amorphous collagen substrate, where they resemble the discoid erythrophore in situ. In this state, they are readily fixed by glutaraldehyde and osmium tetroxide, and are then critical-point dried for whole-cell viewing in the high voltage electron microscope. The organization and fine structure of the erythrophore cytoplast was stereoscopically examined after fixation of the pigment granules in four experimental states: pigment dispersed, pigment aggregated, pigment aggregating, and pigment dispersing. In the dispersed cell, granules are contained in an extensive three-dimensional lattice composed of radially oriented microtubules and a network of fine filaments 3-6 nm in diameter (microtrabeculae), whereas in the aggregated cell, the microtrabecular system is absent, and the majority of the microtubules appear displaced into the cortices on the cytoplasmic surface of the plasma membrane. In cells fixed while aggregating, few microtrabeculae are observed, although formless thickenings are observed in the cortices, on granules, and between clumped granules. In dispersing cells, the microtrabecular system is reformed from material stored in the cortices and with the granules in the centrosphere. These observations suggest that the granules are suspended in a dynamic microtrabecular system that withdraws during pigment aggregation and is restructured during pigment dispersion. The microtubules guide linear granule motion not by defining physical channels, but by a recognizable affinity of microtubules, microtrabeculae, and granules for one another.

Animals↗
PubMed1976

Stereo high-voltage electron microscopy of whole cells of the human diploid line, WI-38.

The human diploid cell line, WI-38, has proven to be an especially good object for high-voltage electron microscopy using whole cells. Cells of intermediate passages were grown on plastic-coated, carbon-shadowed gold grids, fixed with glutaraldehyde, post-fixed with osmium tetroxide, stained with uranyl salts and critical-point dried. The absence of an embedding matrix produces images of increased contrast and resolution. The approach combined with stereo-microscopy has extended our knowledge of cellular ultrastructure. Stereo-images of whole cells reveal nuclei, mitochondria, microtubules, microfilaments, the endoplasmic reticulum and ribosomes in their expected forms. At high magnifications a continuity of microtubules, microfilaments and membranous elements with thin (3-6 nm) strands of the ground substance has been observed. These strands form a three-dimensional lattice or mesh that pervades all parts of the cytoplasm. The entire structure is referred to as a microtrabecular lattice or mesh, the strands being the trabeculae. The inclusion of microtubules, microfilaments, ribosomes and vesicles of the endoplasmic reticulum within the material of the lattice makes them all part of a totally organized cytoplast.

Cell Line↗
PubMed1976

Collagenous and other organizations in mature annelid cuticle and epidermis.

The mature annelid cuticle contains orthogonally oriented collagen in a matrix capped superficially by a dense epicuticle with external corpuscles. The underlying epidermis is a simple columnar epithelium with two major cell types, mucous-secreting cells which secrete through channels in the cuticle to the exterior of the worm, and "supportive" cells which presumably produce and increase the cuticle by secreting into it. The structures of supportive cells, previously interpreted as specialized for establishing interfibrillar collagen order, are revealed by glutaraldehyde fixation as common cellular components without the qualities deemed useful to align collagen. Cell processes which penetrate and sometimes pass completely through the cuticle are not stable, not in geometric order, and lack cilia-like structure. Cilia, unlike the ubiquitous cellular processes, are highly restricted to regions of the epidermis with specialized functions. Cellular control, or other control, of collagen fibrillogenesis remains unestablished.

Animals↗
PubMed1976

Collagen deposition on a preformed grid.

Appearance of collagen fibrils in the cuticle was seen by electron microscopy to be preceded by formation of a finely filamentous matrix material. At first, the fine filaments of the matrix are unorganized. However, signs of orthogonal ordering soon appear in the most superficial portion of the cuticle, and subsequently appear more basally and closer to the underlying epidermis. Meanwhile, fibrils of different staining properties and identifiable as collagen begin to be deposited in the superficial portion of the cuticle, the same region which first showed organized fine filaments. Then, like the fine filaments before them, the collagen fibrils polymerize more basally. Collagen appears to polymerize on the preformed skeleton of fine filaments as though the fine filaments lagen fibrils seems to require direct cellular intervention but occur first in that portion of the cuticle which is furthest away from the underlying epidermis. The fine filaments may be self ordering, extracellular macromolecules which in turn determine the polymerization of collagen fibrils.

Animals↗
PubMed1976

Studies of excitable membranes. II. A comparison of specializations at neuromuscular junctions and nonjunctional sarcolemmas of mammalian fast and slow twitch muscle fibers.

Mammalian fast and slow twitch skeletal muscles are compared by freeze-fracture, thick and thin sectioning, and histochemical techniques using conventional and high voltage electron microscopy. Despite gross morphological differences in endplate structure visualized at relatively low magnifications in this sections, rat extensor digitorum longus (EDL) (fast twitch) and soleus (slow twitch) fibers cannot be distinguished on the basis of size, number, or distribution of molecular specializations of the pre- and postsynaptic junctional membranes exposed by freeze fracturing. Specializations in the cortex of the juxtaneuronal portions of the junctional folds are revealed by high voltage electron stereomicroscopy as a branching, ladder-like filamentous network associated with the putative acetylcholline receptor complexes. These filaments are considered to be involved in restricting the mobility of receptor proteins to the perineuronal aspects of the postynaptic membrane. Although the junctional membranes of both EDL and soleus appear similar, a differential specialization of the secondary synaptic cleft was noted. The extracellular matrix in the bottom of soleus clefts was observed as an ordered system of filamentous "combs," These filamentous arrays have not been detected in EDL junctions. Examination of the extrajunctional sarcolemmas of EDL and soleus reveal additional differences which may be correlated with variations in electrical and contractile properties. For example, particle aggregates termed "square arrays" previously described in the sarcolemmas of some fibers of the rat diaphragm were observed in large numbers in sarcolemmas of EDL fibers but were seldom encountered in soleus fibers. These gross compositional differences in the membranes are discussed in the light of functional differences between fiber types.

Animals↗
PubMed1975

Electron microscopy of critical point dried whole cultured cells.

To determine the overall fine structure of whole, unsectioned cells, cells from rat embryos were cultured on Formvar, glutaraldehyde/osmium-fixed, transferred to grids, dehypdrated, critical point dried, then examined by transmission electron microscopy at either 80 or 1000 kV. In contrast to air-dried material, critical point dried cells revealed each component clearly and with excellent contrast. All normal cytoplasmic structures (including coated vesicles, polyribosomes, microtubules and other fine components) were readily identifiable. Extensive structures such as microtubules and the endoplasmic reticulum (which appear fragmented in sections) were well displayed. At 1000 kV the beam readily penetrated even the thick nuclear and perinuclear cell regions and produced exceptionally crisp images. The methods described provide a simplified approach to the study of overall cell fine structure.

Cell Nucleolus↗