bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ULTRASTRUCTURE OF FROG VENTRICULAR CARDIAC MUSCLE AND ITS RELATIONSHIP TO MECHANISMS OF EXCITATION-CONTRACTION COUPLING
Authors: Staley Nancy A. , Benson Ellis S.
Published: May 2004

Frog ventricular cardiac muscle has structural features which set it apart from frog and mammalian skeletal muscle and mammalian cardiac muscle. In describing these differences, our attention focused chiefly on the distribution of cellular membranes. Abundant inter cellular clefts, the absence of tranverse tubules, and the paucity of sarcotubules, together with exceedingly small cell diameters (less than 5 µ), support the suggestion that the mechanism of excitation-contraction coupling differs in these muscle cells from that now thought to be characteristic of striated muscle such as skeletal muscle and mammalian cardiac muscle. These structural dissimilarities also imply that the mechanism of relaxation in frog ventricular muscle differs from that considered typical of other striated muscles. Additional ultrastructural features of frog ventricular heart muscle include spherical electron-opaque bodies on thin filaments, inconstantly present, forming a rank across the I band about 150 mµ from the Z line, and membrane-bounded dense granules resembling neurosecretory granules. The functional significance of these features is not yet clear.
STUDIES ON THE PHYSIOLOGICAL AND STRUCTURAL CHARACTERISTICS OF RAT INTESTINAL MUCOSA
Authors: Jasper D. K. , Bronk J. R.
Published: May 2004

Sections from mucosal strips and rings of rat jejunum were studied with the light microscope and the electron microscope before and after incubation in a modified Krebs bicarbonate Ringer. Various additions were made to the incubation medium, and their effects on both the structure and the respiratory activity of the mucosal tissue were noted. In those cases in which an amino acid mixture was added, there was a pronounced increase in the rate of respiration. When strips of intestine were used, the presence of the amino acid mixture more than doubled the rate of oxygen consumption. Along with the increased levels of respiration there was a sharp rise in the percentage of mitochondria assuming a condensed ultrastructural conformation. The amino acid mixture did not cause the condensation of jejunal mitochondria if glucose was included in the incubation medium or if 2,4-dinitrophenol was present. The evidence suggests that a high proportion of the jejunal mitochondria assumes a condensed conformation in response to an increased energy demand. Apparently glucose can prevent the amino acid mixture from increasing the energy drain on the oxidative processes in these cells. Although a high rate of respiration was obtained in the presence of dinitrophenol, the studies indicated that mitochondrial condensation was only associated with a high rate of coupled oxidative phosphorylation.
INTRACELLULAR CHARACTERIZATION OF BEAN YELLOW MOSAIC VIRUS-INDUCED INCLUSIONS BY DIFFERENTIAL ENZYME DIGESTION
Authors: Weintraub M. , Ragetli H. W. J.
Published: May 2004

The composition of crystalline inclusions and dense bands in cells of broad bean leaves infected with bean yellow mosaic virus was studied by differential enzymatic digestion. Frozen thick sections were prefixed in glutaraldehyde and exposed to proteinases and nucleases, after which ultrathin sections were prepared for electron microscopy. Examination revealed that the crystals were completely digested by pepsin in 30 min, whereas the dense bands remained intact for the first 20 min, and could not be found after longer periods of digestion. When ultrathin sections of tissues embedded in glycol methacrylate were incubated with the enzymes, pepsin digested the crystals; this left only a filamentous residue which did not disappear after further exposure to pepsin or to RNase. Trypsin had the same effect, but was slower and less consistent. The dense bands were entirely digested in thin sections by pepsin and trypsin. Neither inclusion was affected by RNase or DNase in thick or thin sections. These results demonstrate that the crystals and dense bands are composed entirely or primarily of protein, but there is no evidence that they contain nucleic acid.
AUTOPHAGIC VACUOLES PRODUCED IN VITRO
Authors: Fedorko Martha E. , Hirsch James G. , Cohn Zanvil A.
Published: May 2004

Continuous phase-contrast observations have been made on macrophages following exposure to chloroquine. The initial abnormality is the appearance in the Golgi region of small vacuoles with an intermediate density between that of pinosomes and granules. Over the course of 1–2 hr these vacuoles grow larger and accumulate amorphous material or lipid. Pinosomes or granules frequently fuse with the toxic vacuoles. Chloroquine derivatives can be seen by fluorescence microscopy; the drug is rapidly taken up by macrophages and localized in small foci in the Golgi region. Chloroquine continues to produce vacuoles when pinocytosis is suppressed. Electron microscopic studies of chloroquine effects on macrophages preincubated with colloidal gold to label predominately pinosomes or granules suggest that toxic vacuoles can arise from unlabeled organelles. Later vacuoles regularly acquire gold label, apparently by fusion, from both granules and pinosomes. L cells also develop autophagic vacuoles after exposure to chloroquine. Smooth endoplasmic reticulum apparently is involved early in the autophagic process in these cells. Information now available suggests an initial action of chloroquine on Golgi or smooth endoplasmic reticulum vesicles, and on granules, with alterations in their membranes leading to fusion with one another and with pinosomes.
FINE STRUCTURE OF CELL DIVISION IN CHLAMYDOMONAS REINHARDI
Authors: Johnson Ursula G. , Porter Keith R.
Published: May 2004

Cell division in log-phase cultures of the unicellular, biflagellate alga, Chlamydomonas reinhardi, has been studied with the electron microscope. The two basal bodies of the cell replicate prior to cytokinesis; stages in basal body formation are presented. At the time of cell division, the original basal bodies detach from the flagella, and the four basal bodies appear to be involved in the orientation of the plane of the cleavage furrow. Four sets of microtubules participate in cell division. Spindle microtubules are involved in a mitosis that is marked by the presence of an intact nuclear envelope. A band of microtubules arcs over the mitotic nucleus, indicating the future cleavage plane. A third set of microtubules appears between the daughter nuclei at telophase, and microtubules comprising the "cleavage apparatus" radiate from the basal bodies and extend along both sides of the cleavage furrow during cytokinesis. Features of cell division in C. reinhardi are discussed and related to cell division in other organisms. It is proposed that microtubules participate in the formation of the cleavage furrow in C. reinhardi.
DNA ORGANIZATION IN THE MATURE SPERM OF SEVERAL ORTHOPTERA BY THE METHOD OF POLARIZED FLUORESCENCE MICROSCOPY
Authors: MacInnes James W. , Uretz Robert B.
Published: May 2004

Mature sperm of Acheta domesticus, Acheta assimilis, Nemobius fasciatus, Nemobius confusus, Melanoplus femur-rubrum, Romalea microptera, Scudderia curvicauda, and Ceuthophilus nigricans were examined for DNA configuration by means of polarized fluorescence microscopy. In all cases, the results suggest that the DNA lies in unsupercoiled array, predominantly parallel to the elongate sperm head axes. Detailed calculations of the factors influencing the degree of polarization of the fluorescent emission from supercoiled DNA are contained in an appendix.
MICROTUBULES AND EARLY STAGES OF CELL-PLATE FORMATION IN THE ENDOSPERM OF HAEMANTHUS KATHERINAE BAKER
Authors: Hepler Peter K. , Jackson William T.
Published: May 2004

A fine structure study of the phragmoplast and developing cell plate has been made on glutaraldehyde-osmium tetroxide-fixed, dividing, cultured cells of the liquid endosperm of Haemanthus katherinae Baker. The phragmoplast arises between the telophase nuclei, usually in association with a remnant strand of spindle elements, and consists of an accumulation of microtubules oriented at right angles to the plane of the future cell plate. The microtubules, which are 200–240 A in diameter, occur in small clusters spaced at approximately 0.2–0.3 µ intervals along the plate. Short interconnections interpreted as "cross-bridges" have been observed between individual microtubules. Within each cluster there is an electron-opaque zone about 0.3 µ in width which can be attributed in part to an overlap of microtubules from both sides of the plate and in part to a local accumulation of an amorphous electron-opaque material. During development these dense zones become aligned in a plane which itself defines the plane of the plate. Vesicles, commonly observed in long files, are derived from a cytoplasmic matrix rich in elements of the endoplasmic reticulum and sparse in dictyosomes. They aggregate between the clusters of microtubules and eventually coalesce to form the cell plate.
FAST AND SLOW COMPONENTS IN AXONAL TRANSPORT OF PROTEIN
Authors: McEwen Bruce S. , Grafstein Bernice
Published: May 2004

(a) After injection of labeled leucine into the eye of goldfish, radioactive protein rapidly accumulates in the contralateral optic tectum in the layer containing the synaptic endings of the optic fibers. This material reaches the tectum 6–12 hr after the isotope injection, a fact which indicates that the rate of transport is at least 40 mm per day. (b) This rapidly transported material has been shown to consist exclusively of protein, in which the label remains attached to leucine. (c) Inhibition of protein synthesis in the retina prevents the appearance of the transported protein in the tectum, but inhibition of protein synthesis in the tectum does not. Substances having some of the same properties as leucine, such as cycloleucine and norepinephrine, are not transported to the tectum. These experiments all indicate that the transported protein is synthesized in the retina. However, inhibition of retinal protein synthesis after this protein has been formed does not interfere with the transport mechanism itself. (d) The fast component consists of about 85% particulate material. It may be distinguished from a slowly moving component, transported at 0.4 mm per day, which contains about 5 times as much radioactivity as the fast component, and which consists of 60% particulate matter and 40% soluble protein.
RADIOAUTOGRAPHIC LOCALIZATION OF DEOXYTHYMIDINE TRIPHOSPHATE IN TRADESCANTIA POLLEN GRAINS DURING DNA SYNTHESIS
Authors: Takats S. T.
Published: May 2004

Tradescantia pollen grains, isolated during the period of DNA synthesis in the generative cell, accumulate deoxythymidine triphosphate (dTTP)-3H after incubation with thymidine-3H in the presence of millimolar deoxyadenosine. Most of this dTTP-3H was found to resist extraction by the fixative, cold ethanol-acetic acid, and its location was investigated by radioautography with thin, dry emulsion. Substantial binding of dTTP-3H occurred as an artifact; but when nuclei were isolated from the fixed pollen grains by sonication, it was found that they were differentially labeled: generative nuclei contained dTTP-3H, vegetative nuclei did not. This observation is discussed and is interpreted as evidence supporting the idea that thymidine is phosphorylated only in the generative cell of the pollen grain.
CHANGES IN THE DISTRIBUTION OF A HISTONE IN DORSAL ROOT GANGLION NEURONS DURING DEVELOPMENT
Authors: Kornguth Steven E. , Tomasi Lawrence G.
Published: May 2004

The isolation and cellular localization of a basic protein (histone) from central nervous tissue have been previously reported. In the tissues previously studied (nervous tissue, testis, liver, spleen, kidney, ovary), the basic protein was restricted in distribution to the nuclei of neurons and spermatogonia. In the present study, the temporal appearance of the histone within neurons and the changes in its distribution during ontogenesis were examined. The reaction between a fluorescent immune γ-globulin prepared against this purified tissue-specific histone and the neurons from the dorsal root ganglia of the rat was investigated. The dorsal root ganglia examined were those from fetuses, 2-, 10-, and 40-day-old rats, and from adult rats. At the earliest stages, only the nucleoli reacted. Subsequently, threads of fluorescent material were seen to emerge from the nucleoli. The extent of this reaction between the immune globulin and the threads within the nuclei continued to increase with maturation. No changes in fluorescence localization during development could be seen in the nuclei of neurons in the cerebellum or brain stem. The role that this tissue-specific histone may play in cell function is discussed.
INTRACELLULAR ACCUMULATION OF PROTOCOLLAGEN AND EXTRUSION OF COLLAGEN BY EMBRYONIC CARTILAGE CELLS
Authors: Cooper George W. , Prockop Darwin J.
Published: May 2004

The synthesis of collagen can be interrupted, after the assembly of proline-rich and lysine-rich polypeptide chains called protocollagen, by incubating connective tissues anaerobically. Under these conditions the proline and lysine residues in protocollagen are not hydroxylated to hydroxyproline and hydroxylysine, and protocollagen molecules accumulate intracellularly. Chemical data and radioautographs at the level of the light and electron microscopes indicated that in tissues labeled with proline-3,4-3H under nitrogen, there appeared to be an accumulation of radioactivity over the ground cytoplasm. When the inhibition of protocollagen hydroxylase was reversed by exposing the tissue to oxygen, the accumulated protocollagen-3H was converted to collagen-3H and there was a rapid transfer of label from the ground cytoplasm to the extracellular matrix. There was no significant change in distribution of label over either the Golgi vacuoles or the cisternae of the endoplasmic reticulum. The failure to find a significant change in distribution of label over the Golgi vacuoles or the cisternae does not completely exclude the possibility that these two compartments are involved in the extrusion, but the data are consistent with the simpler notion that the completed collagen molecules pass directly from the ground cytoplasm to the extracellular matrix.
INTERCELLULAR COMMUNICATION AND TISSUE GROWTH
Authors: Jamakosmanović A. , Loewenstein W. R.
Published: May 2004

Intercellular communication was examined in normal and cancerous isolated thyroids with an intracellular electrical technique. The cells of normal thyroid (rat, mouse, hamster, man) communicate, within any given follicle, through permeable junctions. The cells of a wide variety of thyroid cancers (rat, hamster) do not communicate to any detectable degree and have resting membrane potentials lower than those of normal cells.
AN ATYPICAL CRISTA RESEMBLING A "TIGHT JUNCTION" IN BEAN ROOT MITOCHONDRIA
Authors: Newcomb Eldon H. , Steer Martin W. , Hepler Peter K. , Wergin William P.
Published: May 2004

The conformation and structure of an atypical crista found in a small percentage of the mitochondria in root tip cells of Phaseolus vulgaris L. have been studied electron microscopically in material fixed in glutaraldehyde followed by osmium tetroxide. In its transformation into an atypical crista, a normal crista elongates, broadens, and flattens, and the inner leaflets of its apposed unit membranes appear to fuse in a manner analogous to the formation of "tight junctions" between certain animal cells. The result is a large platelike, quintuple-layered structure, 240–260 A thick, whose long axis parallels that of the mitochondrion. The outer layers of the "plate," bordering on the mitochondrial matrix, are thickened and exhibit striking patterns in the micrographs. The structure of the plate is compared with that previously described for tight junctions between animal cells.
MICROINCINERATION, ELECTRON MICROSCOPY, AND ELECTRON DIFFRACTION OF CALCIUM PHOSPHATE-LOADED MITOCHONDRIA
Authors: Thomas Richard S. , Greenawalt John W.
Published: May 2004

Isolated rat liver mitochondria were incubated in vitro under conditions supporting the massive accumulation of calcium and phosphate. Samples were embedded, thin sectioned, and examined in the electron microscope. The intramitochondrial distribution of insoluble or structure-bound mineral substances was studied by electron microscopy coupled with recently developed techniques of high resolution microincineration. As shown previously, the ion-loaded mitochondria acquire large, internal granules which have inherent electron opacity indicative of high mineral content. Study of ash patterns in preselected areas of sections directly confirmed the high mineral content of the granules, and the appearance of the residues was consistent with the copresence in the granules of some organic material. Other mitochondrial structures were almost devoid of mineral. Thin sections of unincubated control mitochondria also were incinerated. They were found to contain appreciable amounts of intrinsic mineral, seemingly associated with membranes. The normal, dense matrix granules commonly seen in unaltered mitochondria could be seen in intact sections of these control preparations, but after burning no definite correspondence of any ash to the granules could be demonstrated. The normal granules perhaps do not contain mineral. Heating experiments on ash patterns of all the preparations demonstrated the thermal stability and crystallizability of the ash. The crystallized ash of the in vitro-produced dense granules was tentatively shown by electron diffraction to be ß-tricalcium phosphate (whitlockite). This, together with evidence from the literature, suggests that the original, noncrystalline mineral may be a colloidal, subcrystalline precursor of calcium-deficient hydroxyapatite. Experiments were performed on synthetic calcium phosphates for comparison. Other possible applications of the microincineration techniques are briefly discussed.
STRUCTURAL FEATURES OF MESOSOMES (CHONDRIOIDS) OF BACILLUS SUBTILIS AFTER FREEZE-ETCHING
Authors: Nanninga N.
Published: May 2004

Freeze-etched cells of Bacillus subtilis have been studied with the electron microscope. The outer surface of the plasma membrane, i.e. the side facing the cell wall, is covered with numerous granules and short strands, each measuring approximately 50 A in diameter. These strands are occasionally seen to enter the cell wall. The inner surface of the plasma membrane, i.e. the side facing the cytoplasm, appears to be sparsely dotted with small particles measuring about 50 A. The envelope of mesosomes differs from the plasma membrane. Blunt protrusions arise from its outer surface; the inner surface appears smooth. Stalked particles, as described by other investigators after negative staining with phosphotungstic acid, were not observed on any membrane surface in our material. Preparations were also made of specimens prefixed in osmium tetroxide prior to freeze-etching. Under these conditions the bacterial membranes appeared to be surprisingly well preserved. In contrast to directly frozen, unfixed cells, some osmium tetroxide-fixed preparations showed a differentiation in cytoplasm and nucleoplasm, which made it possible to observe the close association of the mesosome with the latter.
DIFFERENCES IN ENZYME CONTENT OF AZUROPHIL AND SPECIFIC GRANULES OF POLYMORPHONUCLEAR LEUKOCYTES
Authors: Bainton Dorothy Ford , Farquhar Marilyn G.
Published: May 2004

Histochemical procedures for PMN granule enzymes were carried out on smears prepared from normal rabbit bone marrow, and the smears were examined by light microscopy. For each of the enzymes tested, azo dye and heavy metal techniques were utilized when possible. The distribution and intensity of each reaction were compared to the distribution of azurophil and specific granules in developing PMN. The distribution of peroxidase and six lysosomal enzymes (acid phosphatase, arylsulfatase, ß-galactosidase, ß-glucuronidase, esterase, and 5'-nucleotidase) corresponded to that of azurophil granules. Progranulocytes contained numerous reactive granules, and later stages contained only a few. The distribution of one enzyme, alkaline phosphatase, corresponded to that of specific granules. Reaction product first appeared in myelocytes, and later stages contained numerous reactive granules. The results of tests for lipase and thiolacetic acid esterase were negative at all developmental stages. Both types of granules stained for basic protein and arginine. It is concluded that azurophil and specific granules differ in their enzyme content. Moreover, a given enzyme appears to be restricted to one of the granules. The findings further indicate that azurophil granules are primary lysosomes, since they contain numerous lysosomal, hydrolytic enzymes, but the nature of specific granules is uncertain since, except for alkaline phosphatase, their contents remain unknown.
THE FINE STRUCTURE OF PRONUCLEAR DEVELOPMENT AND FUSION IN THE SEA URCHIN, ARBACIA PUNCTULATA
Authors: Longo Frank J. , Anderson Everett
Published: May 2004

Fertilization events following coalescence of the gamete plasma membranes and culminating in the formation of the zygote nucleus were investigated by light and electron microscopy in the sea urchin, Arbacia punctulata. Shortly after the spermatozoon passes through the fertilization cone, it rotates approximately 180° and comes to rest lateral to its point of entrance. Concomitantly, the nonperforated nuclear envelope of the sperm nucleus undergoes degeneration followed by dispersal of the sperm chromatin and development of the pronuclear envelope. During this reorganization of the sperm nucleus, the sperm aster is formed. The latter is composed of ooplasmic lamellar structures and fasciles of microtubules. The male pronucleus, sperm mitochondrion, and flagellum accompany the sperm aster during its migration. As the pronuclei encounter one another, the surface of the female pronucleus proximal to the advancing male pronucleus becomes highly convoluted. Subsequently, the formation of the zygote nucleus commences with the fusion of the outer and the inner membranes of the pronuclear envelopes, thereby producing a small internuclear bridge and one continuous, perforated zygote nuclear envelope.
PROTEINS IN NUCLEOCYTOPLASMIC INTERACTIONS
Authors: Prescott David , Goldstein Lester
Published: May 2004

The behavior of nuclear proteins in Amoeba proteus was studied by tritiated amino acid labeling, nuclear transplantation, and cytoplasmic amputation. During prophase at least 77% (but probably over 95%) of the nuclear proteins is released to the cytoplasm. These same proteins return to the nucleus within the first 3 hr of interphase. When cytoplasm is amputated from an ameba in mitosis (shen the nuclear proteins are in the cytoplasm), the resultant daughter nuclei are depleted in the labeled nuclear proteins. The degree of depletion is less than proportional to the amount of cytoplasm removed because a portion of rapidly migrating protein (a nuclear protein that is normally shuttling between nucleus and cytoplasm and is thus also present in the cytoplasm) which would normally remain in the cytoplasm is taken up by the reconstituting daughter nuclei. Cytoplasmic fragments cut from mitotic cells are enriched in both major classes of nuclear proteins, i.e. rapidly migrating protein and slow turn-over protein. An interphase nucleus implanted into such an enucleated cell acquires from the cytoplasm essentially all of the excess nuclear proteins of both classes. The data indicate that there is a lack of binding sites in the cytoplasm for the rapidly migrating nuclear protein. The quantitative aspects of the distribution of rapidly migrating protein between the nucleus and the cytoplasm indicate that the distribution is governed primarily by factors within the nucleus.
MODIFICATIONS ULTRASTRUCTURALES DES CELLULES SÉCRÉTRICES DE LA GLANDE PROTHORACIQUE DE VERS À SOIE AU COURS DES DEUX DERNIERS ÂGES LARVAIRES
Authors: Beaulaton J. A.
Published: May 2004

Ultrastructural study of the prothoracic glands of silkworms (Antheraea pernyi and Bombyx mori) at the last two larval stages has shown that the essential modifications which take place during each intermolt affect the chondriome of secretory cells. A description is given of the differentiation of macromitochondria from typical mitochondria by a general swelling, a clearing of the matrix, and the formation of a complex tubular network. The hypothesis of fixation or anaesthesia artifacts has been dismissed because of the persistence of these transformations after different fixations and because of the existence of numerous intermediary stages between these two types of chondriosomes which imply the progressiveness of differentiation. The cytochemical demonstration of mitochondrial DNA fibers suggests that the genetic information, probably present in this type of nucleic acid, controls the differentiation and the specific metabolic activity of these organelles. The frequent relationships observed in Antheraea between the tubules of agranular reticulum and the macromitochondria which are reminiscent of the vacuoles-mitochondria associations of the adrenal cortex, may be related to the transfer of cholesterol and other precursors of steroidogenesis. In the last stages, the macromitochondria become transformed into vacuoles by a disappearance of the tubular network. The correlation revealed between mitochondrial transformations and the cyclical release of ecdysone (65) leads to the conclusion that a prominent fraction of chondriosomes is involved, in relation to the agranular reticulum, in the elaboration of steroid hormones such as ecdysone.
ON THE ROLE OF MICROTUBULES IN MOVEMENT AND ALIGNMENT OF NUCLEI IN VIRUS-INDUCED SYNCYTIA
Authors: Holmes Kathryn V. , Choppin Purnell W.
Published: May 2004

Infection of baby hamster kidney (BHK21-F) cells with the parainfluenza virus SV5 causes rapid and extensive cell fusion. Time-lapse cinematography shows that when cells fuse, their nuclei migrate straight to the center of the syncytium at rates of 1–2 µ/min. Nuclei are often arranged in long, tightly packed, parallel rows in syncytia derived from the fibroblastic BHK21-F cells. Polarization microscopy shows birefringent material between and parallel to these rows of nuclei, and electron microscopy shows bundles of cytoplasmic microtubules, ∼250 A in diameter, and filaments, ∼80 A in diameter, parallel to and between the rows of nuclei. Colchicine treatment causes disappearance of microtubules from BHK21-F cells and an apparent increase in the number of 80-A filaments. Although colchicine-treated, SV5-infected cells fuse, their nuclei do not migrate or form rows but remain randomly scattered through the syncytial cytoplasm. Incubation at 4°C does not disrupt microtubules in BHK21-F cells. Rows of nuclei have been isolated from SV5-induced syncytia, and the nuclei in them have been found to be intimately associated with microtubules but not with other cytoplasmic structures. These results suggest that microtubules demarcate cytoplasmic channels through which nuclei migrate and that they may also be involved in the mechanism of nuclear movement.
INTRACELLULAR TRANSPORT OF SECRETORY PROTEINS IN THE PANCREATIC EXOCRINE CELL
Authors: Jamieson James D. , Palade George E.
Published: May 2004

Experiments have been carried out to determine whether intracellular transport of pancreatic secretory proteins is obligatorily coupled to protein synthesis or whether it is a separable process which can be independently regulated. To this intent, guinea pig pancreatic slices were pulse labeled with leucine-3H for 3 min and incubated post-pulse for 37 min in chase medium containing cycloheximide up to concentrations sufficient to inhibit protein synthesis by 98%. In controls, newly synthesized secretory proteins are transported over this interval to condensing vacuoles of the Golgi complex. Since the latter are recovered in the zymogen granule fraction upon cell fractionation, intracellular transport was assayed by measuring the amount of protein radioactivity found in the zymogen granule fraction after a (3 + 37) min incubation. The results indicated that at maximum inhibition of protein synthesis (5 x 10-4 M cycloheximide), transport proceeded with an efficiency ∼80% of control. Parallel radioautographic studies on intact slices confirmed these data and further indicated that all the steps of intracellular transport, including discharge to the acinar lumen, were independent of protein synthesis. We conclude that: (1) transport and protein synthesis are separable processes; (2) intracellular transport is not the result of a continuous delivery of secretory proteins from attached polysomes to the cisternae of the rough endoplasmic reticulum; and (3) transport is not dependent on the synthesis of "specific" nonsecretory proteins within the time limits tested.
INTRACELLULAR TRANSPORT OF SECRETORY PROTEINS IN THE PANCREATIC EXOCRINE CELL
Authors: Jamieson James D. , Palade George E.
Published: May 2004

Since in the pancreatic exocrine cell synthesis and intracellular transport of secretory proteins can be uncoupled (1), it is possible to examine separately the metabolic requirements of the latter process. To this intent, guinea pig pancreatic slices were pulse labeled with leucine-3H for 3 min and incubated post-pulse for 37 min in chase medium containing 5 x 10-4 M cycloheximide and inhibitors of glycolysis, respiration, or oxidative phosphorylation. In each case, the effect on transport was assessed by measuring the amount of labeled secretory proteins found in zymogen granule fractions isolated from the corresponding slices. This assay is actually a measure of the efficiency of transport of secretory proteins from the cisternae of the rough endoplasmic reticulum (RER) to the condensing vacuoles of the Golgi complex which are recovered in the zymogen granule fraction (16). The results indicate that transport is insensitive to glycolytic inhibitors (fluoride, iodoacetate) but is blocked by respiratory inhibitors (N2, cyanide, Antimycin A) and by inhibitors of oxidative phosphorylation (dinitrophenol, oligomycin). Except for Antimycin A, the effect is reversible. Parallel radioautographic studies and cell fractionation procedures applied to microsomal subfractions have indicated that the energy-dependent step is located between the transitional elements of the RER and the small, smooth-surfaced vesicles at the periphery of the Golgi complex. Radiorespirometric data indicate that the substrates oxidized to support transport are endogenous long-chain fatty acids.
FINE STRUCTURAL ALTERATIONS OF INTERPHASE NUCLEI OF LYMPHOCYTES STIMULATED TO GROWTH ACTIVITY IN VITRO
Authors: Tokuyasu K. , Madden S. C. , Zeldis L. J.
Published: May 2004

This report describes fine structural changes of interphase nuclei of human peripheral blood lymphocytes stimulated to growth by short-term culture with phytohemagglutinin. Chromatin is found highly labile, its changes accompanying the sequential increases of RNA and DNA synthesis which are known to occur in lymphocyte cultures. In "resting" lymphocytes, abundant condensed chromatin appears as a network of large and small aggregates. Early in the response to phytohemagglutinin, small aggregates disappear during increase of diffuse chromatin regions. Small aggregates soon reappear, probably resulting from disaggregation of large masses of condensed chromatin. Loosened and highly dispersed forms then appear prior to the formation of prophase chromosomes. The loosened state is found by radioautography to be most active in DNA synthesis. Small nucleoli of resting lymphocytes have concentric agranular, fibrillar, and granular zones with small amounts of intranucleolar chromatin. Enlarging interphase nucleoli change chiefly (1) by increase in amount of intranucleolar chromatin and alteration of its state of aggregation and (2) by increase in granular components in close association with fibrillar components.
A BIOCHEMICAL AND HISTOCHEMICAL STUDY OF GLUTAMIC OXALACETIC TRANSAMINASE ACTIVITY OF RAT HEPATIC MITOCHONDRIA FIXED IN SITU AND IN VITRO
Authors: Lee Sin Hang , Torack Richard M.
Published: May 2004

Rat liver perfused in situ briefly with a glutaraldehyde-formaldehyde mixture was homogenized in isotonic sucrose. The mitochondria, isolated from a homogenate of the perfused liver by differential centrifugation, assumed a slender and compact appearance similar to those often seen in an intact cell. The glutamic oxalacetic transaminase (GOT) activity of this mitochondrial fraction survived an additional formaldehyde fixation and was studied by biochemical and histochemical methods. The biochemical assay of the enzyme activity revealed that the activity was only slightly less than that of an unfixed mitochondrial fraction. The reaction product due to mitochondrial GOT activity was found to be localized to the cristae, as had been demonstrated in an intact liver cell. GOT activity of the mitochondrial fraction isolated from fresh liver tissue homogenate in 0.25 M sucrose was inactivated readily by either glutaraldehyde or formaldehyde and was no longer demonstrable by biochemical and histochemical methods after fixation.
Morphological Features of DNA Macromolecules as Seen with the Electron Microscope
Authors: Hall Cecil E. , Litt Michael
Published: May 2004

Desoxyribosenucleic acid molecules isolated from salmon sperm were studied with the electron microscope. The essential step in the technique which makes it possible to visualize the individual molecules consists in a preparative step wherein the materials are supported on the extremely smooth surface of cleaved mica where they are shadow-cast with platinum, which is then backed with a supporting film and stripped for observation in the usual manner. The DNA, which was originally about 8 million molecular weight, was also examined after fragmentation by sonic vibration. The fragments show a certain degree of rigidity and the ends generally terminate abruptly, indicating that the double helices of the Watson-Crick model both break close to the same place. DNA molecules heated to temperatures between 90 and 100°C, coil up into amorphous patches, although a few apparently unaltered molecules survive such heating.
Electron Microscopy of Peripheral Nerves and Neuromuscular Junctions in the Wasp Leg
Authors: Edwards George A. , Ruska Helmut , de Harven Étienne
Published: May 2004

The peripheral nerve branch innervating the femoral muscles of the common yellow jacket (Vespula carolina) has been found to possess a thick lemnoblast basement membrane and a complex mesaxon. The term "tunicated nerve" is proposed to designate the type of peripheral nerve in which one or several axons are loosely mantled by meandering, cytoplasm-enclosing membranes of the lemnoblast.

The peripheral axon courses longitudinally in a groove in the muscle fiber between the plasma membrane of the muscle fiber and a cap formed by lemnoblast and tracheoblast. The junction is characterized by apposition of plasma membranes of axon and muscle fiber, abundant mitochondria, and synaptic vesicles in the axon, and aggregates of "aposynaptic granules" plus mitochondria and endoplasmic reticulum on the muscle side of the synapse. Unlike the vertebrate striated muscle fiber, no complex infolding of the synapsing plasma membrane of the muscle fiber occurs.

The "connecting tissue" of the insect is formed by tracheoblasts, their basement membranes, and the basement membranes of other cells. Further mechanical support is given by the ramifying tracheoles.

The physiologic roles of the specialized structures are considered.
Biological Activity of Fractions Obtained by Differential Centrifugation of the Bovine Adrenal Cortex
Authors: Schultz Richard L. , Meyer Roland K.
Published: May 2004

This study is an attempt to correlate adrenocortical hormonal activity with various cell fractions obtained by homogenization and differential centrifugation of bovine adrenocortical tissue. Bioassays involving the decrease in circulating eosinophils and sodium retention were employed for the estimation of the glucocorticoids and mineralocorticoids respectively. The supernatant was the most active fraction in both bioassays, while the microsome and mitochondrial fractions demonstrated varying degrees of activity. The total nitrogen, lipide phosphorus, and cholesterol contents of the fractions were determined. The microsome fraction contained a relatively higher amount of lipide phosphorus and a marked amount of cholesterol.
A Histochemical Method for the Demonstration of Diphosphopyridine Nucleotide Diaphorase
Authors: Nachlas Marvin M. , Walker Donald G. , Seligman Arnold M.
Published: May 2004

The present investigation concerning the histochemical demonstration of DPN diaphorase follows the development of a new reagent, Nitro-BT, which has already been used successfully for the cytochemical localization of the succinic dehydrogenase system. The most consistently favorable results were obtained with the lactate-lactic dehydrogenase system buffered at pH 7.4. Using sections of rat kidney and stomach, it was found that the intensity of stain was optimal after 15 minutes incubation at 37°C., conducted aerobically.

By appropriate variations in the substrate mixture it was possible to selectively demonstrate the histochemical distribution of certain DPN-linked dehydrogenases in addition to DPN diaphorase. This was made possible by the special distribution of some of these dehydrogenases which distinguished them from one another. Of the dehydrogenases studied the distribution pattern of ß-hydroxybutyric dehydrogenase was the most singular. In the gastric mucosa ß-hydroxybutyric dehydrogenase was restricted to the cells of the mucous lining epithelium and the gland necks; and in the kidney the enzyme was limited to the cells of the proximal convoluted tubule and thick limbs of Henle's loop. In contrast, lactic dehydrogenase like DPN diaphorase was demonstrable in almost all cytologic elements of both the stomach and the kidney.
The Ultrastructure of Schmidt-Lanterman Clefts and Related Shearing Defects of the Myelin Sheath
Authors: Robertson J. David
Published: May 2004

Schmidt-Lanterman clefts in frog sciatic nerves have been studied in thin sections by electron microscopy utilizing permanganate fixation and araldite embedding. It is shown that they are shearing defects in myelin in which the lamellae are separated widely at the major dense lines. Each lamella consisting of two apposed Schwann cell unit membranes ∼ 75 A across traverses the cleft intact. The unit membranes composing each lamella sometimes are slightly (∼ 50 to 100 A) separated in the clefts. The layers between the lamellae contain membranous structures which may be components of the endoplasmic reticulum. These layers are continuous with the outer layer of Schwann cytoplasm and the thin and inconstant cytoplasmic layer next to the axon (Mauthner's sheath). Each of these layers in perfect clefts constitutes a long helical pathway through the myelin from the axon. One of these is connected with Schwann cytoplasm and the other directly with the outside. A type of cross-sectional shearing defect, not hitherto recognized, is described and shown to be a kind of Schmidt-Lanterman cleft.

Incomplete clefts are seen and interpreted as representing stages in a dynamic process whereby the myelin lamellae may be constantly separating and coming together again in life.
Evidence for Two Metabolically Distinct Types of Ribonucleic Acid in Chromatin and Nucleoli
Authors: McMaster-Kaye Rachel , Taylor J. Herbert
Published: May 2004

Patterns of radioisotope incorporation are useful characteristics in describing cellular RNA fractions, and have indicated a distinctive "nuclear" RNA.

In order to characterize the RNA fractions of the two nuclear components, nucleoli and chromatin, and to determine thereby the precise localization of the RNA typical of isolated nuclei, time-courses of P32 incorporation into nucleolar, chromosomal, and cytoplasmic RNA of Drosophila salivary glands have been determined from autoradiograms. Two experiments are reported which cover 12 and 18 hour periods, including an initial 2 hour feeding on P32. Concentrations of RNA-P32 (identified by ribonuclease digestion) were determined by grain counts.

After 1 hour only the nucleolar RNA is labelled. Activity is detectible in chromosomal and cytoplasmic RNA after the 2nd hour. The nucleolar fraction reaches its maximum activity shortly after transfer of the larvae to non-radioactive food, the other fractions several hours later. Maximum activities persist in the chromosomal and cytoplasmic fractions; nucleolar activity decreases after the 9th hour.

The observed differences in times at which incorporation begins and maximum activities are reached, and in maintenance of maximum activities indicate that chromosomal and nucleolar RNA are distinct fractions. The metabolic characteristics which have been ascribed to "nuclear" RNA apply only to the nucleolar fraction.
Electron Microscope Study of a Cell-Free Induced Leukemia of the Mouse: A Preliminary Report
Authors: de Harven Étienne , Friend Charlotte
Published: May 2004

Preliminary results of an electron microscope study of a leukemia of the mouse transmissible by cell-free filtrates are reported. In twelve out of forty-seven specimens examined, virus-like particles were observed. So far, these particles have not been observed in control, non-leukemic animals. They are located inside the cytoplasm of leukemic cells which infiltrate the spleen or the liver. Their diameter is approximately 78 mµ. Their resemblance to other particles recently described in different mouse tumors is stressed. Their significance and, in correlation with ultrafiltration data, their possible etiological meaning are discussed.
Autoradiographic Studies of the Utilization of Ca45 by the Chick Embryo
Authors: Johnston Perry M.
Published: May 2004

Calcium-45 was injected into the dense albumen of fertile hen's eggs, to the extent of 25 µc. per egg. The eggs were incubated under standard conditions and three or more embryos removed daily and fixed in 10 per cent neutral formalin. Stripping-film autoradiograms were prepared from paraffin sections of the tibiofibulae. Exposure varied with the isotope concentration. The tissue sections with their autoradiograms in place were stained with dilute Giemsa, while other sections were stained with hematoxylin-azure-eosin and by von Kossa to demonstrate bone salt.

At about 9 days, Ca45 is found in the cartilage template both intra- and extracellularly. Between 9 and 11 days, a primary diaphyseal lamella is deposited which is largely acellular. The lamella is eroded by capillaries from the periosteum and a resorption center is established in the cartilage. New lamellae of bone are deposited centrifugally in an imbricated pattern. Bone matrix formation precedes calcification by about 1 to ½ days, and calcification in a particular lamella is not uniform. Endochondral bone formation is described, as well as calcification of the epiphyseal/diaphyseal cartilage. Calcium-45 occurs intracellularly in the osteocyte during bone formation.
An Electron Microscope Study of the Contractile Vacuole in Tokophrya infusionum
Authors: Rudzinska Maria A.
Published: May 2004

Contractile vacuoles are organelles that collect fluid from the cytoplasm and expel it to the outside. After each discharge (systole), they appear again and expand (diastole). They are widely distributed among Protozoa, and have been found also in some fresh water algae, sponges, and recently in some blood cells of the frog, guinea pig, and man.

In spite of the extensive work on the contractile vacuole, very little is known concerning its mode of operation. An electron microscope study of a suctorian Tokophrya infusionum provided an opportunity to study thin sections of contractile vacuoles, and in these some structures were found which could be part of a mechanism for the systolic and diastolic motions the organelle displays.

In Tokophrya, as in Suctoria and Ciliata in general, the contractile vacuole has a permanent canal connecting it with the outside. The canal appears to have a very elaborate structure and is composed of three parts: (1) a pore; (2) a channel; and (3) a narrow tubule located in a papilla protruding into the cavity of the contractile vacuole. Whereas the pore and channel have fixed dimensions and are permanently widely open, the tubule has a changeable diameter. At diastole it is so narrow (about 25 to 30 mµ in diameter) that it could be regarded as closed, while at systole it is widely open.

It is assumed that the change in diameter is due to the contraction of numerous fine fibrils (about 180 A thick) which are radially disposed around the canal in form of a truncated cone, with its tip at the channel, and its base at the vacuolar membrane. It seems most probable that the broadening of the tubule results in discharge of the content of the contractile vacuole.

In the vicinity of the very thin limiting vacuolar membrane, small vesicles and canaliculi of the endoplasmic reticulum, very small dense particles, and mitochondria may be found. In addition, rows of closely packed vesicles are present in this region, and in other parts of the cytoplasm. It is suggested that they might represent dictyosome-like bodies, responsible for withdrawing fluids from the cytoplasm and then conveying them to the contractile vacuole, contributing to its expansion at diastole.
Surface Responses in Cultured Fibroblasts Elicited by Ethylenediaminetetraacetic Acid
Authors: Dornfeld Ernst J. , Owczarzak Alfred
Published: May 2004

Cultures of chick heart fibroblasts were perfused with the chelating agent ethylenediaminetetraacetic acid (EDTA). Cellular responses were observed under phase optics and recorded by time-lapse cinemicrography.

In interphasic fibroblasts, EDTA induces cellular contraction followed by continuous protrusion and retraction of ectoplasmic blebs ("surface bubbling"), formation of motile vermiform processes, and production of rotatory ectoplasmic swellings. The contraction and surface bubbling closely resemble the metaphase contraction and "anaphase bubbling" normally displayed by cultured fibroblasts.

In dividing cells, EDTA does not affect metaphases, but anaphase bubbling appears and persists; telophasic expansion and migration of daughter cells are prevented. Initiation of new mitoses occurs during and after exposure to EDTA.

No cellular responses are induced by calcium, magnesium, or ferrous chelates of EDTA. The EDTA elects are completely reversible on removal of the chelating agent, resulting in the restoration of the normal interphasic cell form and the normal expansion and migration of mitotic products.

The EDTA effects are interpreted to result from the chelation and removal of divalent cations from the cell surface. Possible relations to surface activities observed in normal mitosis are considered, and an hypothesis is presented regarding the role of the developing spindle in cation transfer.
Studies on Shell Formation
Authors: Watabe Norimitsu , Sharp D. Gordon , Wilbur Karl M.
Published: May 2004

Electron microscope observations have been made by means of the replica method on growth processes of calcite crystals of the nacreous layer of the shell of the oyster, Crassostrea virginica. Layer formation is initiated by the secretion of a conchiolin matrix and the deposition of rounded crystal seeds on or in this material. In some areas crystal seeds are elongate and within a given area show a similar orientation, probably due to slower deposition. The seeds appear to increase in size by dendritic growth, and smaller seeds become incorporated into larger ones which come into contact to form a single layer. With further growth, crystals overlap, forming a step-like arrangement. The direction of growth is frequently different in neighboring regions. Crystal seeds deposited on crystal surfaces are usually elongate and oriented. Well developed crystals have a tabular idiomorphic form and are parallel in their growth. Rounded and irregular crystals were also observed. The crystals show reticular structure with units of the order of 100 A and striations corresponding with the rhombohedral axes of the crystals. The role of the mantle is discussed in relation to the growth patterns of crystals and shell structure.