bluuebunny/crossref_metadata_2025 huggingface dataset:
REGULATION OF INITIATION OF DNA SYNTHESIS IN CHINESE HAMSTER CELLS
Authors: Tobey R. A. , Ley K. D.
Published: May 2004

Suspension cultures of Chinese hamster cells (line CHO) were grown to stationary phase (approximately 8–9 x 105 cells/ml) in F-10 medium. Cells remained viable (95%) for at least 80 hr in stationary phase, and essentially all of the cells were in G1 Upon resuspension or dilution with fresh medium, the cells were induced to resume traverse of the life cycle in in synchrony, and the patterns of DNA synthesis and division were similar to those observed in cultures prepared by mitotic selection. Immediately after dilution, the rates of synthesis of RNA and protein increased threefold. This system provides a simple technique for production of large quantities of highly synchronized cells and may ultimately provide information on the biochemical mechanisms regulating cell-cycle traverse.
THE ULTRASTRUCTURE OF THE NEUROMUSCULAR JUNCTIONS OF MAMMALIAN RED, WHITE, AND INTERMEDIATE SKELETAL MUSCLE FIBERS
Authors: Padykula Helen A. , Gauthier Geraldine F.
Published: May 2004

Distinct ultrastructural differences exist at the neuromuscular junctions of red, white, and intermediate fibers of a mammalian twitch skeletal muscle (albino rat diaphragm). The primary criteria for recognizing the three fiber types are differences in fiber diameter, mitochondrial content, and width of the Z line. In the red fiber the neuromuscular relationship presents the least sarcoplasmic and axoplasmic surface at each contact. Points of contact are relatively discrete and separate, and axonal terminals are small and elliptical. The junctional folds are relatively shallow, sparse, and irregular in arrangement. Axoplasmic vesicles are moderate in number, and sarcoplasmic vesicles are sparse. In the white fiber long, flat axonal terminals present considerable axoplasmic surface. Vast sarcoplasmic surface area is created by long, branching, closely spaced junctional folds that may merge with folds at adjacent contacts to occupy a more continuous and widespread area. Axoplasmic and sarcoplasmic vesicles are numerous. Both axoplasmic and sarcoplasmic mitochondria of the white fiber usually contain intramitochondrial granules. The intermediate fiber has large axonal terminals that are associated with the most widely spaced and deepest junctional folds. In all three fiber types, the junctional sarcoplasm is rich in free ribosomes, cisternae of granular endoplasmic reticulum, and randomly distributed microtubules.
IMMUNOGLOBULIN SYNTHESIS AND SECRETION
Authors: Schenkein Isaac , Uhr Jonathan W.
Published: May 2004

This study was designed to determine the time in the intracellular life of immunoglobulin when the carbohydrate moieties are added. Plasma cells from a mouse myeloma tumor were exposed to glucosamine-3H (a "bridge" sugar), galactose-3H, or leucine-3H. With each of the above isotopes, the percentage of total radioactive immunoglobulin that has been secreted after different periods of labeling and the extent to which puromycin prevented incorporation into immunoglobulin were determined. The results indicate that both galactose and glucosamine (in its N-acetyl form) become covalently incorporated into immunoglobulin G late in its intracellular life and suggest that glucosamine is also added onto nascent polypeptide chains (i.e., on polyribosomes).
IMMUNOGLOBULIN SYNTHESIS AND SECRETION
Authors: Zagury Daniel , Uhr Jonathan W. , Jamieson James D. , Palade George E.
Published: May 2004

The subcellular sites of synthesis and route of intracellular transfer of immunoglobulin G (IgG) have been investigated by electron microscope radioautography with precursors used for the polypeptide chain (leucine-3H) and for the carbohydrate moieties (galactose-3H and glucosamine-3H). For this purpose, plasma cells from a mouse myeloma tumor were labeled with appropriate precursors and the distribution of radioautographic grains was determined at the end of the labeling period and after varying times of incubation in unlabeled medium. The results indicated that the polypeptide backbone is synthesized in a region of the cell occupied by the rough endoplasmic reticulum (RER) and is transported from there to the region of the Golgi complex. Galactose is incorporated in IgG primarily at the level of the Golgi complex, whereas the incorporation of glucosamine appears to take place both in the RER and in the Golgi complex. From the Golgi complex, the completed IgG molecules reach the plasma membrane and are discharged extracellularly. The latter route of transport and the mechanism of discharge are not understood but may be mediated via smooth-surfaced vesicles.
PROLIFERATIVE BEHAVIOR OF DIFFERENTIATING CELLS IN THE DEVELOPING RAT PAROTID GLAND
Authors: Redman Robert S. , Sreebny Leo M.
Published: May 2004

Parotid glands of litters of rats at age intervals from 20 days in utero to 100 days were assayed for DNA content and examined by light- and electron-microscopy. The age differences in total DNA and DNA concentration indicated that there was a rapid rate of proliferation of parenchymal cells until 25 postnatal days, after which the rate declined rapidly, and that there was a rapid increase in cell size between 18 and 25 days. These findings were substantiated by histologic observations, such as the presence of numerous mitotic figures until 25 days of age, and the rapid maturation of the acinar cells between 18 and 25 days. These data suggest that the acinar cells of the rat parotid gland comprise an expanding cell population. Light- and electron-microscopic observations consistently indicated that cells with mitotic figures were about as well differentiated as other parenchymal cells at all stages of gland development, including mature acinar cells observed at ages 23 and 25 days. These observations support the view that the division of cells in advanced stages of differentiation may be important in the growth of certain organs and tissues.
HUMAN MONOCYTES AND MACROPHAGES
Authors: Hanifin J. M. , Cline M. J.
Published: May 2004

PPD-sensitized monocytes and macrophages from tuberculin-positive subjects are both capable of inducing blastogenic transformation of autologous lymphocytes. Incorporation of thymidine-3H and morphological transformation were always greater in lymphocyte cultures containing macrophages than in those containing monocytes. More lymphocytes entered the first detectable S phase in cultures containing macrophages. Lymphocyte DNA synthesis occurred as early as 40 hr of culture and always in cells in contact with mononuclear phagocytes. By 120–144 hr, many transformed lymphocytes were free in suspension; at the same time, the "immunological cluster" had increased greatly in size and contained transformed and untransformed lymphocytes. The greater effectiveness of macrophages at induction of lymphocyte transformation may be related to the efficiency of this cell type at trapping antigen and its effectiveness at making contact with and binding lymphocytes.
OSMIUM STAINING OF ENDOPLASMIC RETICULUM AND MITOCHONDRIA IN THE RAT ADRENAL CORTEX
Authors: Friend Daniel S. , Brassil Gail E.
Published: May 2004

The zona fasciculata of the rat adrenal cortex synthesizes and secretes glucocorticoids. As observed after aldehyde fixation, the cells in this zone contain an extensive endoplasmic reticulum (ER), a small Golgi apparatus, a moderate number of lipid droplets, and abundant mitochondria with tubulovesicular cristae. Numerous areas within the endoplasmic reticulum and mitochondrial cristae appear clear. In addition, a small percentage of mitochondria encompasses large, clear areas. After immersion of finely minced adrenal cortex in unbuffered 2% OsO4 (40–48 hr at 40°C), deposits of osmium are seen within the Golgi apparatus, the entirety of the ER, and occasionally within mitochondria. In some mitochondria, the deposits are within cristae; in others, within vacuoles; in still others, in both cristae and vacuoles. These localizations correspond best to the clear areas found in aldehyde-fixed tissue. Osmium is not deposited in lipid droplets, in bar-containing inclusions, in mitochondrial matrix inclusions, or in the peripheral, outer mitochondrial spaces. Addition of zinc-iodide to OsO4 increases the amount of Golgi apparatus and mitochondrial staining. Adrenocorticotropin (ACTH) does not affect the localization of deposits; hypophysectomy decreases mitochondrial staining. This study (a) emphasizes the necessity for electron microscopic confirmation of osmium localization when this technique is used as a Golgi apparatus stain; and (b) suggests that the ER-staining pattern may be consistent in cells actively synthesizing steroids or steroid-like compounds.
CYTOPLASMIC FILAMENTS OF AMOEBA PROTEUS
Authors: Pollard Thomas D. , Ito Susumu
Published: May 2004

The role of filaments in consistency changes and movement in a motile cytoplasmic extract of Amoeba proteus was investigated by correlating light and electron microscopic observations with viscosity measurements. The extract is prepared by the method of Thompson and Wolpert (1963). At 0°C, this extract is nonmotile and similar in structure to ameba cytoplasm, consisting of groundplasm, vesicles, mitochondria, and a few 160 A filaments. The extract undergoes striking ATP-stimulated streaming when warmed to 22°C. Two phases of movement are distinguished. During the first phase, the apparent viscosity usually increases and numerous 50–70 A filaments appear in samples of the extract prepared for electron microscopy, suggesting that the increase in viscosity in caused, at least in part, by the formation of these thin filaments. During this initial phase of ATP-stimulated movement, these thin filaments are not detectable by phase-contrast or polarization microscopy, but later, in the second phase of movement, 70 A filaments aggregate to form birefringent microscopic fibrils. A preparation of pure groundplasm with no 160 A filaments or membranous organelles exhibits little or no ATP-stimulated movement, but 50–70 A filaments form and aggregate into birefringent fibrils. This observation and the structural relationship of the 70 A and the 160 A filaments in the motile extract suggest that both types of filaments may be required for movement. These two types of filaments, 50–70 A and 160 A, are also present in the cytoplasm of intact amebas. Fixed cells could not be used to study the distribution of these filaments during natural ameboid movement because of difficulties in preserving the normal structure of the ameba during preparation for electron microscopy.
GLUTAMATE UPTAKE BY A STIMULATED INSECT NERVE MUSCLE PREPARATION
Authors: Faeder Isabelle R. , Salpeter Miriam M.
Published: May 2004

Recent reports suggest that glutamate may be the excitatory neuromuscular transmitter in insects. In this study, glutamate uptake by isolated cockroach nerve muscle preparations was investigated by means of chemical and electron microscope radioautographic techniques. We found that the preparation had a high affinity for glutamate and that nerve stimulation enhanced glutamate uptake. Chemical studies showed that the average tissue concentration of glutamate bound during a 1 hr incubation period in 10-5 M glutamate-3H after nerve stimulation was 2.8 x 10-5 M. Less than 1% of the radioactivity was present in the perchloric acid-precipitated protein fraction. Using electron microscope radioautography, we observed that sheath cells showed the highest glutamate concentration of all cellular compartments. Uptake was greater at neuromuscular junctions than in other regions of the tissue. The data suggest a possible mechanism for transmitter inactivation and protection of synapses from high blood glutamate.
STRUCTURE-FUNCTION RELATIONSHIPS IN THE ADIPOSE CELL
Authors: Cushman Samuel W. , Rizack Martin A.
Published: May 2004

Serum albumin stimulates the uptake of U-glucose-14C and the incorporation of 14C-counts into triglyceride glycerol and inhibits the incorporation of 14C-counts into triglyceride fatty acids by isolated adipose cells; insulin and epinephrine enhance these effects. In the absence of hormones, these responses to albumin increase with increasing albumin concentration. In the presence of insulin, a qualitatively similar pattern of increasing responses to albumin is observed; the enhancement of each response by insulin is, however, only slightly potentiated by higher albumin concentrations. In contrast, in the presence of epinephrine, these responses to albumin are maximal at the lowest albumin concentration tested, 0.1%; the enhancement of each response by epinephrine is similarly maximal at 0.1% albumin, but decreases rapidly as the albumin concentration is raised. Increasing serum albumin concentrations do, however, stimulate the release of fatty acids and glycerol by epinephrine-treated cells increasingly until a plateau, determined by the epinephrine dose, is reached. These data support the suggestion that intracellular fatty acid levels function in the regulation of adipose cell activity, and further suggest that serum albumin plays a role in determining the metabolic fate of these fatty acids.
NUCLEAR MEMBRANES FROM MAMMALIAN LIVER
Authors: Kleinig Hans
Published: May 2004

The qualitative and quantitative lipid composition of nuclei and nuclear membranes from pig and rat liver were determined. These determinations were compared with the corresponding data obtained for microsomes from the same material after similar treatments. The results indicate that, at least, by far the major part of the nuclear lipids is located in the membranes of the nuclear envelope. The phospholipid pattern of the nuclear membranes and the endoplasmic reticulum (ER) membranes in general is widely identical in both species. As a striking difference in the lipid composition, however, a fourfold increase of esterified cholesterol in the nuclear membranes was found. In a quantitative approach the ratio of total surface area of the nuclear lipids to the total surface area of the nuclear envelope membranes was calculated as being 3.6, a value which fairly approximates the requirements of a bimolecular lipid leaflet model.
CYTOCHEMICAL AND DEVELOPMENTAL CHANGES IN MICROBODIES (GLYOXYSOMES) AND RELATED ORGANELLES OF CASTOR BEAN ENDOSPERM
Authors: Vigil Eugene L.
Published: May 2004

Structural changes in endosperm cells of germinating castor beans were examined and complemented with a cytochemical analysis of staining with diaminobenzidine (DAB). Deposition of oxidized DAB occurred only in microbodies due to the presence of catalase, and in cell walls associated with peroxidase activity. Seedling development paralleled the disappearance of spherosomes (lipid bodies) and matrix of aleurone grains in endosperm cells. 6 to 7 days after germination, a cross-section through the endosperm contained cells in all stages of development and senescence beginning at the seed coat and progressing inward to the cotyledons. Part of this aging process involved vacuole formation by fusion of aleurone grain membranes. This coincided with an increase in microbodies (glyoxsomes), mitochondria, plastids with an elaborate tubular network, and the formation of a new protein body referred to as a dilated cisterna, which is structurally and biochemically distinct from microbodies although both apparently develop from rough endoplasmic reticulum (ER). In vacuolate cells microbodies are the most numerous organelle and are intimately associated with spherosomes and dilated cisternae. This phenomenon is discussed in relation to the biochemical activities of these organelles. Turnover of microbodies involves sequestration into autophagic vacuoles as intact organelles which still retain catalase activity. Crystalloids present in microbodies develop by condensation of matrix protein and are the principal site of catalase formerly in the matrix.
RETARDATION OF PERIPHERAL NERVE MYELINATION IN MICE TREATED WITH INHIBITORS OF CHOLESTEROL BIOSYNTHESIS
Authors: Rawlins Frank A. , Uzman Betty G.
Published: May 2004

The effect of two inhibitors of cholesterol biosynthesis, triparanol and AY 9944, on peripheral nerve myelination, was studied. Suckling mice were intraperitoneally injected with both drugs on 3 consecutive days and were sacrificed 6 hr after the last injection; others were suckled by an injected mother and sacrificed at 2½ days of age. A single mouse which had been injected with both drugs at 1, 2, and 3 days of age was sacrificed 2 wk after the last injection.

Membranous and crystalline intracytoplasmic inclusions were observed in the Schwann cells of the sciatic nerves of all the experimental animals. Both the number of unmyelinated single axons and the number of myelin lamellae around each myelinating axon in the sciatic nerves were recorded for treated mice and of mice suckled by treated mothers.

The sciatic nerve of the experimental mice contained a larger proportion of unmyelinated single axons and smaller numbers of myelin lamellae around the myelinating axons, when compared with age-matched controls. The results suggest that a decrease of endogenous cholesterol in suckling mice may affect peripheral nerve myelination in two ways: by retarding the "triggering" of myelination in unmyelinated axons and by decreasing the rate of myelination already in progress.
SURFACE STRUCTURE OF ISOLATED NEURONS
Authors: Hamberger Anders , Hansson Hans-Arne , Sjöstrand Johan
Published: May 2004

Freehand, isolated neuronal perikarya from the hypoglossal nucleus of the rabbit have been examined with light-and electron-microscopy (transmission and scanning). The surface of the cell bodies was largely covered with spherical particles which were 0.5–2 µ in diameter. Transmission electron microscopy proved that the spherical particles were synaptic nerve terminals. Crush of the hypoglossal nerve which leads to chromatolysis and swelling of the neuronal cell bodies results in a conspicuous reduction in the number of terminals attached to the surface of hypoglossal neurons. This effect was observed both for isolated neurons and in tissue sections. The effect is considered in relation to earlier reported variations in the adherence of neuropil to isolated neuronal perikarya. The functional importance of nerve ending detachment in connection with nerve injury is discussed.
THE REACTION OF RAT MAST CELLS TO POLYLYSINE
Authors: Padawer Jacques
Published: May 2004

The effects of a single intraperitoneal injection of polyamino acids (lysine, glutamic, aspartic) on mast cells of the rat are described. In vitro interaction of mast-cell components with these polyamino acids is also explored. Poly-DL-lysine (but not the acidic amino acids) has both immediate (minutes-hours) and long-term (days-weeks) effects on mast cells. At the dosage selected, some cells evidence rapid fusion of granules and degranulation, but without concomitant swelling; most display intracellular changes only. Neither degranulation nor granule fusion appears to be lethal. Rather, these spur the cell to greater synthetic activity which involves first the Golgi apparatus and subsequently also the endoplasmic reticulum. Early involvement of macrophages and eosinophils is described. Sequential studies after polylysine injection support the following concepts: (a) mast-cell granules exist as "physiological sets," several being confined to a common membranous "sac;" (b) each set can respond independently to applied stimuli; (c) each set can connect directly to the extracellular milieu; (d) poly-DL-lysine binds directly to the granules and stabilizes them; it is not readily digested; (e) mast-cell granules are produced directly; they do not arise by intake of exogenous polysaccharides. It is hypothesized that mast-cell granules are topologically outside the cell while held intimately within extensive cytoplasmic folds and recesses. Mast cells may function by causing intercellular connective tissue fluids to percolate over their granules which may process this fluid in some as yet undefined way(s).
COMPARTMENTALIZATION OF THE DEVELOPING MACRONUCLEUS FOLLOWING CONJUGATION IN STYLONYCHIA AND EUPLOTES
Authors: Kloetzel John A.
Published: May 2004

The development of the macronucleus following conjugation in the hypotrichous ciliates Euplotes and Stylonychia has been examined with the electron microscope. Banded polytene chromosomes can be seen in thin sections of the macronuclear anlagen during the early periods of exconjugant development. As the chromosomes reach their maximum state of polyteny, sheets of fibrous material appear between the chromosomes and transect the chromosomes in the interband regions. Individual bands of the polytene chromosomes thus appear to be isolated in separate compartments. Subsequently, during the stage when the bulk of the polytenic DNA is degraded (1), these compartments swell, resulting in a nucleus packed with thousands of separate spherical chambers. Individual chromosomes are no longer discernible. The anlagen retain this compartmentalized condition for several hours, at the end of which time aggregates of dense material form within many of the compartments. The partitioning layers disperse shortly before replication bands appear within the elongating anlagen, initiating the second period of DNA synthesis characteristic of macronuclear development in these hypotrichs. The evidence presented here suggests that the "chromatin granules" seen in the mature vegetative macronucleus represent the material of single bands of the polytene chromosomes seen during the earlier stages of macronuclear development. The possibility is also discussed that the degradation of DNA in the polytene chromosomes may be genetically selective, which would result in a somatic macronucleus with a different genetic constitution than that of the micronucleus from which it was derived.
HISTOCHEMICAL STAINING AND CHARACTERIZATION OF GLYCOPROTEINS IN ACID-SECRETING CELLS OF FROG STOMACH
Authors: Forte Trudy M. , Forte John G.
Published: May 2004

Glycoproteins were histochemically localized in oxyntic cells of the frog stomach by staining with periodic acid-silver methenamine. Reduction of silver was most intense on (a) the outer aspect of the apical plasmalemma, (b) within the tubular smooth membrane system characteristic of oxyntic cells, and (c) within cisternae and vesicles of the Golgi complex. Other membrane components such as those from the mitochondria, nucleus, junctional complex, lateral and basal cell membranes showed little or no stainability. Gastric mucosal homogenates were fractionated by centrifugation for further morphological and chemical analysis. The staining reaction of the microsomal fraction (40,000 g x 60 min) was similar to that of the tubular membranous components of intact oxyntic cells. Carbohydrate analyses showed that all cell fractions are extremely low in acidic sugars, uronic and sialic acids, while neutral sugars and hexosamines are relatively abundant. The microsomal fraction contains the largest proportion of carbohydrates, ca. 9% of the fat-free dry weight. Another distinguishing feature is that glucosamine is the only detectable hexosamine in the microsomal fraction. These histochemical and chemical data indicate that neutral glycoproteins are associated with membranous components which have been implicated in the process of HCl secretion by oxyntic cells. The staining pattern within the cells supports the hypothesis of interrelationships between the Golgi membranes, tubular smooth membranes, and apical surface membrane.
REGULATION OF INITIATION OF DNA SYNTHESIS IN CHINESE HAMSTER CELLS
Authors: Ley K. D. , Tobey R. A.
Published: May 2004

Suspension cultures of Chinese hamster cells (line CHO), which had stopped dividing and were arrested in G1 following growth to high cell concentrations in F-10 medium, could be induced to reinitiate DNA synthesis and to divide in synchrony upon addition of the appropriate amounts of isoleucine and glutamine. Both amino acids were required to initiate resumption of cell-cycle traverse. Deficiencies in other amino acids contained in F-10 medium did not result in accumulation of cells in G1, indicating a specific action produced by limiting quantities of isoleucine and glutamine. In the presence of sufficient glutamine, approximately 2 x 10-6 M isoleucine was required for all cells to initiate DNA synthesis in a population initially containing 1.5 x 105 cells/ml. Under similar conditions, about 4 x 10-6 M isoleucine was required for all G1-arrested cells to progress through cell division. In contrast, 1 x 10-4 M glutamine was necessary for maximum initiation of DNA synthesis in G1 cells, along with sufficient isoleucine. A technique for rapid production of G1-arrested cells is described in which cells from an exponentially growing population placed in F-10 medium deficient in both isoleucine and glutamine or isoleucine alone accumulated in G1 after 30 hr.
THE CELL JUNCTION IN A LAMELLIBRANCH GILL CILIATED EPITHELIUM
Authors: Satir P. , Gilula N. B.
Published: May 2004

The junctional complex in the gill epithelium of the freshwater mussel (Elliptio complanatus) consists of an intermediary junction followed by a 2–3 µ long septate junction. Homologous and heterologous cell pairs are connected by this junction. After fixation with 1% OsO4 containing 1% potassium pyroantimonate, electron microscopy of the gill reveals deposits of electron-opaque precipitate, specifically and consistently localized along cellular membranes. In both junctional and nonjunctional membrane regions, the precipitate usefully outlines the convolutions without obliterating the 150 A intercellular space, which suggests the rarity or absence of either vertebrate-type gap or tight junctions along the entire cell border. The precipitate appears on the cytoplasmic side of the limiting unit membranes of frontal (F), laterofrontal (LF), intermediate (I), lateral (L), and postlateral (PL) cells. The membrane surfaces of certain vesicles of the smooth endoplasmic reticulum, of multivesicular bodies, and of mitochondrial cristae contain precipitate, as does the nucleolus. In other portions of the cell, precipitate is largely absent. The amount of over-all deposition is variable and depends on the treatment of the tissue prior to fixation. Deposition is usually enhanced by pretreatment with 40 mM NaCl as opposed to 40 mM KCl, which suggests that the precipitate is in part sodium pyroantimonate. Treatment with 0.2 mM ouabain does not enhance deposition. Regional differentiation of cell membranes with respect to their ability to precipitate pyroantimonate is found in at least three instances: (a) between the ciliary membranes and other portions of the cell membrane: the precipitate terminates abruptly at the ciliary base, (b) between the LF and I cell borders: the precipitate is asymmetric, favoring the LF side of the junction, and (c) between the septate junctional membrane and adjacent membrane: the precipitate occurs periodically throughout the septate junction region with the periodicity corresponding to the spacing of the septa. This suggests that different regions of the cell membrane may have differing ion permeability properties and, in particular, that the septa may be the regions of high ion permeability in the septate junction.
STUDIES OF THE TRIAD
Authors: Franzini-Armstrong Clara
Published: May 2004

The structure of the junction between sarcoplasmic reticulum (SR) and transverse tubular (T) system at the triad has been studied in twitch fibers of the frog. The junction is formed by flattened surfaces of the SR lateral sacs and the T-system tubule, which face each other at a distance of 120–140 A. At periodic intervals of about 300 A, the SR membrane forms small projections, whose tips are joined to the T system membrane by some amorphous material. The SR projections and the amorphous material are here called SR feet. The feet are disposed in two parallel rows, two such rows being present on either side of the T-system tubule. The junctional area between the feet is apparently empty. The feet cover no more than 30% of the T system surface area and 3% of the total SR area. The functional significance of this interpretation of the junctional structure is discussed.
THE EFFECTS OF HIGH HYDROSTATIC PRESSURE ON THE MICROTUBULES OF TETRAHYMENA PYRIFORMIS
Authors: Kennedy John R. , Zimmerman Arthur M.
Published: May 2004

Exposure of Tetrahymena pyriformis to 7,500 or 10,000 psi of hydrostatic pressure for 2, 5, or 10 min intervals results in a change in cell shape and ciliary activity. Shape changes occur concurrently with a degradation of longitudinal microtubules in a posterior to anterior direction. High pressure also causes a disruption of ciliary activity. Fine structural analysis reveals a breakdown (presumably microtubule depolymerization) of the central ciliary microtubules. The depolymerization begins at the junction of the central ciliary microtubules with the axosome and progresses distally along the ciliary shaft for a distance of about 0.5 µ.
DURATION OF PREMEIOTIC DEOXYRIBONUCLEIC ACID SYNTHESIS AND THE STAGES OF PROPHASE I IN RABBIT OOCYTES
Authors: Kennelly J. J. , Foote R. H. , Jones R. C.
Published: May 2004

To estimate the duration of oocyte DNA synthesis 36, 3-day-old female rabbits received 3, 6, 9, 12, 15, or 18 injections of tritiated thymidine (thy-3H) at hourly intervals. The ovaries, removed at 1, 10, or 20 days after the first injection, were radioautographed. Counts made of the number of silver grains associated with oocyte nuclei in meiotic Prophase I indicate that the duration of DNA synthesis is between 9 and 12 hr. To determine the length of the stages of meiotic Prophase I, a group of 2-3-day-old rabbits was given a single sub-cutaneous injection of thy-3H, and the ovaries were removed at hourly and/or daily intervals after treatment. The minimum duration of leptotene was 3 hr and the maximum duration probably was less than 8 hr. The maximum durations of zygotene, pachytene, and diplotene were estimated to be 44, 216, and 96 hr, respectively. The interval from the end of oogonial DNA synthesis to the beginning ofpremeiotic DNA synthesis (G2 + Mitosis + G1) appeared to be less than 6 hr.
QUANTITATIVE ASPECTS OF TRANSMITTER RELEASE
Authors: Bittner George D. , Kennedy Donald
Published: May 2004

The opener-stretcher motor neuron in crayfish makes 50 endings upon each of 1200 muscle fibers. We have calculated the quantal content of junctional potentials produced by individual terminals and by the whole cell at various physiological frequencies. The results show that when the motor neuron is active at 20 impulses/second, it releases 50 quanta/impulse per muscle fiber, or a total of 4.5 x 109 quanta/hr. These figures are similar to those for vertebrate muscles per fiber, but larger for the entire neuron because the opener motor unit is so large. On the basis that the quanta correspond to synaptic vesicles each containing 103–104 molecules of transmitter, the release rate must be around 10-11 mole/hr. This value is within an order of magnitude of the release figures obtained for mammalian neurons by collecting transmitter in perfusates, but it is far lower than the value reported for a crustacean inhibitory neuron. If the membrane materials surrounding each vesicle were lost in the release process, the replacement synthesis would involve 24 mm2 of membrane/hr. We conclude that the metabolic load in terms of transmitter synthesis is probably sustainable, but that the release mechanism must operate in such a way that vesicle membrane materials are neither lost nor incorporated into the terminal membrane.
THE CHEMICAL NATURE OF KERATOHYALIN GRANULES OF THE EPIDERMIS
Authors: Matoltsy A. Gedeon , Matoltsy Margit N.
Published: May 2004

Keratohyalin granules were isolated in the native form from the epidermis of newborn rats by the use of citric acid and a detergent. The isolated granules revealed a fine granular substructure in the electron microscope similar to that seen in situ. Analyses of amino acids by automated column-chromatography showed that proline and cystine are present in large proportions whereas histidine is present in a small amount. Accordingly, it was concluded that keratohyalin represents a sulfur-rich amorphous precursor of the horny cell content, rather than a sulfur-poor side product of the keratinization process, or a unique histidine-rich protein as proposed by in situ histochemical and radioautographic studies.
ISOLATION AND BIOCHEMICAL CHARACTERIZATION OF BRUSH BORDERS FROM RABBIT KIDNEY
Authors: Berger Sosamma J. , Sacktor Bertram
Published: May 2004

A technique for the isolation of intact brush borders from rabbit renal cortex was evaluated. The procedure was monitored by phase and electron microscopy and marker enzymes, i.e. ATP:NMN adenylyl transferase, nuclear; cytochrome oxidase, mitochondrial; ß-glucuronidase, lysosomal; and glucose-6-Pase, microsomal; and indicated an essentially pure preparation of brush borders. The disaccharidase, trehalase, previously reported in renal tubules, was localized uniquely in brush borders. Maltase was also found; the specific activities of the two enzymes in the brush borders were increased 10- to 20-fold. Other disaccharidases, such as sucrase, isomaltase, lactase, and cellobiase, were absent. It is suggested that trehalase and maltase are appropriate candidates for marker enzymes of the renal brush border. Isolated brush borders possessed a ouabain-sensitive (Na+ + K+) ATPase, an oligomycin-insensitive Mg++ ATPase, and a Ca++-activated ATPase. Alkaline phosphatases, dephosphorylating ß-glycero-P, and trehalose-6-P were also present. The specific activities of these enzymes were increased three-to-five fold in the brush-border preparations; however, activities were found in other subcellular fractions of the renal cortex. Hexokinase, although evident in the isolated brush border, was found prominently associated with other membranous fractions. Phosphoglucomutase and UDPG pyrophosphorylase were localized in the soluble fraction of the renal cortex.
METABOLISM OF BILIRUBIN BY A CLONAL STRAIN OF RAT HEPATOMA CELLS
Authors: Rugstad Hans E. , Robinson Stephen H. , Yannoni Claudine , Tashjian Armen H.
Published: May 2004

These studies demonstrate that the MH1C1 strain of rat hepatoma cells has the ability to take up and conjugate bilirubin and then excrete the conjugated pigment into the culture medium. On incubation with unconjugated bilirubin, the average rate of appearance of conjugated bilirubin in the medium was 4.4 ± 0.20 µg per mg of cell protein per hour (mean ± SE). The products formed from bilirubin by MH1C1 cells were chromatographically identical to those found in normal rat bile. Assay of bilirubin UDP glucuronyl transferase activity in homogenates of MH1C1 cells gave a value of 3.3 ± 0.50 µg of conjugated pigment formed per mg protein per hour, only moderately less than the enzyme activity of liver from normal rats. Rat fibroblasts in culture did not conjugate bilirubin, nor did they contain bilirubin UDP-glucuronyl transferase activity. As in living animals, flavaspidic acid inhibited bilirubin metabolism by MH1C1 cells, suggesting that the mechanism for bilirubin uptake is similar to that of normal liver. In contrast to the findings in animals, however, preincubation of MH1C1 cells with phenobarbital led to only minimal enhancement of pigment conjugation. MH1C1 cells represent the first example of a clonal strain of cells in culture in which many of the pathways of hepatic bilirubin metabolism remain intact. They should, therefore, serve as a useful model for studies of bile pigment metabolism which are not easily performed in the living animal.
GROWTH AND DIFFERENTIATION OF CYTOPLASMIC MEMBRANES IN THE COURSE OF LIPOPROTEIN GRANULE SYNTHESIS IN THE HEPATIC CELL
Authors: Claude Albert
Published: May 2004

The synthesis of "very low" density lipoprotein in liver cells is characterized by the fact that the synthesized products, mostly triglycerides, are processed in the form of discrete, size-limited granules or globules, about 400 A in diameter. The present investigation has been made possible in part by the use of a fixative (OsO4 in bidistilled H2O at pH 6.0, in the absence of electrolytes) particularly effective in preserving cytoplasmic membranes and lipids, and giving them high stainability and differential contrast. Under these technical conditions, the lipoprotein granules retain their morphology and high density to electrons practically unaltered, and may serve as tracers in determining their route of transport from the sites of synthesis, starting at the rough-smooth ER junctions, to the lumen of Golgi concentrating vesicles. From the observations, it may be deduced that, along with lipoprotein granule synthesis and transport, there are also production and transfer of new membranes in the form of tubular extensions of smooth ER network which, by progressive fusion and coalescence, participate in the elaboration of fenestrated plates and solid Golgi sacs. In contradistinction to the entire process of liver lipoprotein granule synthesis, transport, and segregation, as reported in the present paper, appears to constitute a developmental sequence which includes the following communicating compartments, in consecutive order: cisternae of rough ER where proteins and possibly phospholipids are synthesized, smooth ER network where triglycerides are synthesized and transported in the form of dense granules, fusion of smooth ER tubular extensions into Golgi fenestrated plates, and further coalescence into solid Golgi sacs, ending in the segregation of the granules in appended concentrating vesicles, or detached "secretory vesicles." It seems that it is this progressive evolution in growth and configuration of membranes which is reflected in the so called polarity, from forming to mature faces, of the Golgi apparatus.
LONG-TERM ORGAN CULTURE OF THE SALAMANDER HEART
Authors: Millhouse Edward W. , Chiakulas John J. , Scheving Lawrence E.
Published: May 2004

Beating salamander hearts were maintained in tissue culture for periods ranging from 1 to 6 months. After 1, 3, or 6 months of culture, six hearts, along with six control hearts, were fixed for electron microscopy.

In control tissue, the sarcoplasmic reticulum usually demonstrated the normal pattern of paired, linearly arranged membranes, although in some cases, the reticulum showed a variation from these membranes to a series of small vesicles. There was no evidence of a T-system of tubules in any of the material examined. Desmosome-Z band complexes were observed in almost all sections of both control and experimental material. A possible role of these complexes in the excitation-contraction mechanism is discussed.

In 3 month cultured material, alterations in normal myofibrillar pattern occurred. Small segments of myofibrils branched from one Z band to join the Z band of an adjacent myofibril, or appeared to be fraying out into the sarcoplasm. In 6 month cultured material, myofibrils were fragmented into short segments from which myofilaments frayed out into the sarcoplasm. This filamentous material may be remnants of myofilaments.

Despite the morphological changes in myofibrils, the heart pulsation rate, established at the beginning, was maintained throughout the culture period. It is suggested that the alterations, observed in the experimental material, occurred in elements not essential for heart beat maintenance, or that these alterations have not yet progressed to a critical point of affecting the heart beat.
INTRACELLULAR DISTRIBUTION OF LOW MOLECULAR WEIGHT RNA IN CHIRONOMUS TENTANS
Authors: Egyházi E. , Daneholt B. , Edström J.-E. , Lambert B. , Ringborg U.
Published: May 2004

Low molecular weight RNA species are described in isolated nuclear components and cytoplasm of salivary gland cells of Chironomus tentans. In addition to 4S and 5S RNA and RNA in the 4–5S range previously described, at least three other components in the range below 16S are present. RNA, the molecular weight of which was estimated to 2.3 x 105 and designed 10S RNA, can be observed only in nucleoli; other RNA, the molecular weight of which was estimated to 1.3 x 105 and designed 8S RNA, was detected in the chromosomes, the nuclear sap, and the cytoplasm but not in the nucleoli; and a third type of RNA, the molecular weight of which was estimated to 8.5 x 104 and designed 7S RNA, was present in nucleoli, chromosomes, nuclear sap, and cytoplasm. The substituted benzimidazole, 5,6-dichloro-1 (ß-D-ribofuranosyl)benzimidazole (DRB), which gives a differential inhibition of the labeling of heterodisperse, mainly high molecular weight RNA in the chromosomes, does not inhibit the labeling of 8S RNA. The relative amounts of label in 8S RNA and 4–5S RNA (including 4S RNA and 5S RNA) in different isolated chromosomes, are distributed in proportion to the chromosomal DNA contents. The 8S RNA as well as the 7S RNA show a relative accumulation in chromosomes and nuclear sap with prolonged incubation time and are in this respect similar to intranuclear low molecular weight RNA species described by previous workers. Our data suggest, however, that these two types of RNA may differ in an important aspect from the previously described types since they are also present in the cytoplasm.
NUCLEOLAR AGING IN TETRAHYMENA DURING THE CULTURAL GROWTH CYCLE
Authors: Satir Birgit , Dirksen Ellen Roter
Published: May 2004

Nucelolar morphology was studied by electron microscopy in control and actinomycin D-treated populations of Tetrahymena pyriformis (W) during the cultural growth cycle. Nucleoli exhibit an "aging" cycle concomitant with the cultural growth cycle, but independent of the individual cell cycle. Four different stages in the course of this aging process have been defined. Stage 1 occurs upon inoculation (low number of cells per milliliter) and lasts through lag and accelerating growth phases. In this stage, many small nucleoli are found at the nuclear periphery. In stages 2 and 3, nucleolar fusion begins. Stage 2 dominates the first half of logarithmic growth, and stage 3 dominates the second half. In late decelerating growth phase, the nucleoli enter stage 4. In this stage, only a few large nucleoli are present and these are apparently inactive in ribosome production. In stationary phase, where total RNA remains constant, only stage 4 nucleoli are present. The relative preponderance of granular vs. fibrous components in the nucleoli changes during this cycle, the granular component dominating stage 1 nucleoli and the fibrillar, stage 4 nucleoli. There is a shortening of the intermediate nucleolar stages in the treated cultures; fusion occurs early and is now pronounced. Not enough ribosomes accumulate to carry the treated cultures through the number of generations equivalent to those of the control, which produces a premature stationary phase.
THE FINE STRUCTURE OF COCKROACH CAMPANIFORM SENSILLA
Authors: Moran David T. , Chapman Kent M. , Ellis Richard A.
Published: May 2004

Campaniform sensilla on cockroach legs provide a good model system for the study of mechanoreceptive sensory transduction. This paper describes the structure of campaniform sensilla on the cockroach tibia as revealed by light- and electron-microscopy. Campaniform sensilla are proprioceptive mechanoreceptors associated with the exoskeleton. The function of each sensillum centers around a single primary sense cell, a large bipolar neuron whose 40 µ-wide cell body is available for electrophysiological investigation with intracellular microelectrodes. Its axon travels to the central nervous system; its dendrite gives rise to a modified cilium which is associated with the cuticle. The tip of the 20 µ-long dendrite contains a basal body, from which arises a 9 + 0 connecting cilium. This cilium passes through a canal in the cuticle, and expands in diameter to become the sensory process, a membrane-limited bundle of 350–1000 parallel microtubules. The tip of the sensory process is firmly attached to a thin cap of exocuticle; mechanical depression of this cap, which probably occurs during walking movements, effectively stimulates the sensillum. The hypothesis is presented that the microtubules of the sensory process play an important role in mechanoelectric transduction in cockroach campaniform sensilla.
ULTRASTRUCTURE AND CALCIUM TRANSPORT IN CRUSTACEAN MUSCLE MICROSOMES
Authors: Baskin R. J.
Published: May 2004

Fragmented sarcoplasmic reticulum (FSR) from crustacean muscle was examined following preparation by a variety of electron microscopic techniques. The 30–40 A particles which appeared on the outer surface of FSR vesicles following negative staining were not observed following preparation by freeze-drying, freeze-etching, thin sectioning, or critical-point drying. Crustacean FSR exhibited high values of calcium uptake and extensive nodular formation in the presence of oxalate. 80–90 A diameter membrane particles were seen in freeze-etch preparations of both intact lobster muscle and FSR vesicles. Thin sections of FSR vesicles revealed a membrane thickness of 60–70 A. The membrane appeared to be triple layered, each layer having a thickness of 20–25 A.
THE DEPENDENCE OF CECROPIA YOLK FORMATION IN VITRO ON SPECIFIC BLOOD PROTEINS
Authors: Hausman Steven J. , Anderson Lucy M. , Telfer William H.
Published: May 2004

The capacity of cecropia vitellogenic follicles to form yolk during short-term in vitro incubation in female blood was analyzed by labeling with fluorescein-conjugated serum globulin, tritiated cecropia blood proteins, or tritiated amino acid. As judged by fluorescence microscopy or autoradiography, yolk formation during 3–8 hr in vitro was similar in rate and in protein uptake specificity to that observed in vivo. When follicles were incubated in cecropia male blood, 6% gamma globulin, or cecropia saline, the yolk produced was markedly inferior in quality and quantity to that generated in female blood. Purified preparations of vitellogenin, the primary female blood protein deposited in the yolk, were equivalent to whole female blood in supporting yolk formation; this protein seems, therefore, to have a specific stimulatory role. An enhancement of the rate of pinocytosis at the oocyte surface by vitellogenin is postulated.
THE M BAND
Authors: Kundrat Ellen , Pepe Frank A.
Published: May 2004

The M band can be extracted from fibrils suspended in 5 mM Tris buffer, pH 8.0, for 15 min. The M band is completely removed only from fibrils of sarcomere lengths greater than 2.1 µ. Extraction does not alter the fluorescent antimyosin staining pattern of the A band, thus providing strong evidence that no alteration of the structural integrity of the thick filament has occurred. Fluorescent antibody staining of the M band of unextracted fibrils can be prevented specifically by absorbing the fluorescent antibody with extracted M band material prior to staining. This verifies the specificity of the extraction procedure.
STUDIES ON SEEDS
Authors: Mollenhauer Hilton H. , Totten Clara
Published: May 2004

At least two kinds of lipid vesicles are present in pea and bean cotyledons which can be recognized at seed maturity on the basis of whether they do or do not interassociate into lipid vesicle sheets. Those that do interassociate into sheets are also characterized by (a) their association with plastids or plasma membranes during dormancy, and (b) the unique transformation into flattened saccules that they undergo during the first few days of seed germination. These interassociated (or composite) lipid vesicles have been found in only a few seeds and may be restricted to certain classes of plants and/or certain states of cellular development.

Lipid vesicle-to-saccule transformation is predominantly confined to the germinating seed. However, some lipid vesicle-derived saccules are already present in some cells even before the seed reaches maturity. These partially transformed vesicles and saccules remain unchanged over dormancy, and then resume their transformation when the seed is germinated. This suggests that some stages of seed germination are already underway before the seed reaches maturity and are only resumed at seed germination.

The lipid vesicles that do not interassociate into sheets (i.e., the simple lipid vesicles) are present in all tissues at all states of cellular development. These vesicles do not undergo any conspicuous structural changes during development.