bluuebunny/crossref_metadata_2025 huggingface dataset:
Alterations in Nuclear Ribonucleic Acid Metabolism Induced by Kinetin
Authors: Guttman Ruth
Published: May 2004

Removal of deoxyribonucleic acid from meristematic onion root cells grown in solutions of kinetin, followed by metachromatic staining in azure B bromide, indicated the presence of appreciable amounts of ribonucleic acid in nuclei exposed to the cell division factor.
AN ELECTRON MICROSCOPE STUDY OF THE EMBRYOLOGY OF THE INTERCALATED DISC IN THE HEART OF THE RABBIT
Authors: Muir Alan R.
Published: May 2004

Prenatal and postnatal cardiac muscle from rabbits has been studied by electron microscopy, after osmium fixation and methacrylate embedding. The observations showed that

1. Cell membranes divide the muscle into cellular units from the youngest embryo which was studied (9½ days after coitus) until the adult state.

2. The embryonic muscle cells contain only one nucleus, whereas the adult cell may be multinucleated.

3. At all stages of development, wherever a myofibrillar axis crosses a cellular boundary, the myofilaments are interrupted by an intercalated disc.

4. With age, increase in size and complexity of the discs render them recognisable by the light microscope.
EFFECT OF GAMMA IRRADIATION ON THE DESOXYRIBONUCLEASE II ACTIVITY OF ISOLATED MITOCHONDRIA
Authors: Okada Shigefumi , Peachey Lee D.
Published: May 2004

1. Exposure of isolated liver mitochondria to high doses of gamma rays from a Co60 source causes the level of DNase II activity to increase. Treatment of the mitochondria with sonic vibration causes a further elevation of the activity to a level which is independent of the prior radiation dose.

2. Such increased mitochondrial DNase II activity appears to be due to the "structural damage" of the subcellular particulates caused by the ionizing radiation. Other methods of disrupting the mitochondrial structure also cause increased DNase II activity. A causal relationship between the structural alteration and the increased enzymatic activity is postulated.

3. The DNase II activity appears to be closely associated with the structural elements of the mitochondria and remains associated with the fragments after irradiation.

4. Upon irradiation, the mitochondrial suspension releases ultraviolet-absorbing materials which are probably nucleotide in nature.

5. The possibility of localization of DNase activity in the lysosome fraction of de Duve (15) is discussed. It is felt that DNase II is at least in part a mitochondrial enzyme and that probably the conclusions drawn here would be applicable to any DNase II present in the lysosomes as well.

6. Irradiation of whole liver homogenate causes no increased DNase II activity. The experiments do not provide any information on the presence or action of protective substances in the homogenate.
CELLULAR DIFFERENTIATION IN THE KIDNEYS OF NEWBORN MICE STUDIED WITH THE ELECTRON MICROSCOPE
Authors: Clark Sam L.
Published: May 2004

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.
EXPERIMENTALLY INDUCED CHROMOSOME ABERRATIONS IN PLANTS
Authors: Kihlman B. A.
Published: May 2004

The finding of Lilly and Thoday that potassium cyanide produces structural chromosome changes in root tips of Vicia faba was confirmed. Like mustards, diepoxides, and maleic hydrazide, potassium cyanide seems to act on cells at early interphase. A tendency of cyanide breaks to be concentrated in heterochromatic segments of the chromosomes was evident. The production of chromosome aberrations by cyanide proved to be practically unaffected by the temperature during treatment. In agreement with Lilly and Thoday, the effect of potassium cyanide was found to be dependent on oxygen tension during treatment. The effect of potassium cyanide increases with increasing oxygen concentration up to 100 per cent oxygen. In the absence of oxygen, potassium cyanide was not completely inactive, but produced a low, though significant frequency of aberrations. Pretreatments with 2.4-dinitrophenol did not influence the effect of potassium cyanide.

When bean roots were treated with potassium cyanide before a treatment with 8-ethoxycaffeine, or at the same time as they were treated with 8-ethoxycaffeine, the effect of 8-ethoxycaffeine was almost completely suppressed.

The effects of a number of other heavy metal complexing agents were also tested. Sodium fluoride, potassium thiocyanate, carbon monoxide, o-phenanthroline, 2.2-bipyridine, and sodium azide were without radiomimetic effect under the conditions employed, and so was a mixture of sodium azide and sodium fluoride. A low, but quite significant, radiomimetic effect was obtained after treatments with sodium diethyldithiocarbamate, cupferron, and 8-hydroxyquinoline. Under anaerobic conditions, the effects of cyanide and cupferron were both quantitatively and qualitatively indistinguishable. Unlike the effect of cyanide, the effect of cupferron was not enhanced by the presence of oxygen.

The effects of the same heavy metal complexing agents were tested on the activities of the enzymes catalase and peroxidase. The activities of both of these enzymes were found to be totally inhibited only by potassium cyanide. In the other cases, little correlation was found between ability to inhibit the activities of these enzymes and ability to produce chromosome aberrations.

In a number of experiments, hydrogen peroxide was found to be without radiomimetic effect, whether alone or in combination with potassium cyanide. t-Butyl hydroperoxide proved to be active. The effect of t-butyl hydroperoxide was substantially increased by pretreatments with 2.4.-dinitrophenol.

The results are discussed, and it is concluded that the observations made do not support the hypothesis that hydrogen peroxide is involved in the production of chromosome aberrations by potassium cyanide. The possibility that organic peroxides are involved cannot be excluded on the bases of the experimental results. As an alternative hypothesis, it is suggested that iron or other heavy metals are present in the chromosomes and that cyanide and other heavy metal complexing agents produce chromosome aberrations by reacting with these metals.
STRUCTURE AND DEVELOPMENT OF THE CHLOROPLAST IN CHLAMYDOMONAS
Authors: Sager Ruth , Palade George E.
Published: May 2004

The cytoplasmic organization of a normal green strain of the alga Chlamydomonas reinhardi has been investigated with the electron microscope using thin sections of OsO4 fixed material.

The detailed organization of the chloroplast has been of special interest. The chloroplast, a cup-shaped organelle, surrounded by a double membrane, consists of: (1) discs about 1 micron in diameter, considered to represent the basic structural unit of the chloroplast, and each composed of a pair of membranes joined at their ends to form a flat closed vesicle; the discs are grouped into stacks resembling the grana of higher plants; (2) matrix material of low density in which the discs are embedded; (3) starch grains; (4) the pyrenoid, a non-lamellar region associated with starch synthesis, and containing tubules which connect with the lamellae; (5) the eyespot, a differentiated region containing two or three plates of hexagonally packed, carotenoid-containing granules, located between discs, and associated with phototaxis.

In addition to the chloroplast, the cytoplasm contains various membranous and granular components, including mitochondria, endoplasmic reticulum, and dictyosomes, identified on the basis of morphological comparability with structures seen in animal cells. The nucleus, not investigated in detail in this study, contains a large, granular nucleolus and is surrounded by a nuclear envelope which is provided with pores and exhibits instances of continuity with the endoplasmic reticulum of the cytoplasm.
A STUDY OF THE STRUCTURE OF SPLENIC SINUSES IN MAN AND IN THE ALBINO RAT WITH THE LIGHT MICROSCOPE AND THE ELECTRON MICROSCOPE
Authors: Weiss Leon
Published: May 2004

The splenic sinuses in the spleens of 5 human beings and 7 albino rats have been studied in the light microscope and electron microscope after fixation in Dalton's fluid and Palade's fluid and embedding in n-butyl methacrylate.

Splenic sinuses are tortuous vascular channels of large but variable diameter which represent the first venous vessels in the spleen and make up almost the entire red pulp in man and in rats. These vessels are composed of reticulo-endothelial cells flattened to endothelial form and sheathed by a netted reticulum. The luminal surface of the endothelium is made highly irregular by delicate and variable cytoplasmic protrusions, slender corridors separating adjacent endothelial cells, anastomotic openings to other sinuses, bulgings of entire cells, and even thrusts of endothelium spanning the sinai lumen. The supporting reticulum presents a well developed latticed appearance in tangential sections of sinuses, but in most cuts is punctate or linear.

The reticulum is composed of strands without limiting membranes, which, in substance, are amorphous and resemble basement membrane. Material identical in appearance to the substance of the reticulum may be present in the endothelium, suggesting that the reticulum is formed by endothelial cells. The endothelium also contains deposits of presumed ferritin and hemosiderin. The extreme luminal bulgings of endothelium suggest production of circulating monocytes or lymphocytes by detachment of endothelial cells.

Sinuses are patent and collapsed to varying degrees. Patent sinuses are separated by collapsed sinuses and these collapsed sinuses appear to constitute splenic (Billroth) cords.
TOPOGRAPHY OF THE ORGANIC COMPONENTS IN MOTHER-OF-PEARL
Authors: Grégoire Charles
Published: May 2004

1. The topography of the organic components (conchiolin) has been investigated on positive, postshadow-cast, formvar, and carbon replicas of mother-of-pearl from shells of a Cephalopod, of two Gastropods, and of six Pelecypods. All these shells are characterized by a true nacreous inner shell layer.

2. The material included normal shell surfaces, fragments of cleavage obtained by fracture, and surfaces polished tangentially and transversally to the inner surface of the shells. Replicas of these surfaces were prepared before and after etching of graded heaviness, induced by a chelating agent (sequestrene NA 2, titriplex III). Micrographs of the successive steps of the process of corrosion have been recorded.

3. Corrosion unmasked, on the nacreous surfaces, organic membranes or sheets, running as continuous formations in between adjacent mineral lamellae, and separating the individual crystals of aragonite which are aligned in rows and constitute each lamella.

4. The interlamellar sheets of material exhibit a reticulated structure, which is especially visible in preparations orientated tangentially to the lamellae and to the tabular surface of the aragonite crystals. The pattern of this lace-like structure, different in the various species studied, appeared in the same species as closely similar to that reported previously in leaflets of thoroughly decalcified mother-of-pearl, dissociated by ultrasonic waves. The present results support former conclusions with regard to the existence of taxonomic differences between Cephalopods, Gastropods, and Pelecypods in the morphological organization of the organic phase within mother-of-pearl.
The Spermatid Cell Membrane in Melanoplus differentialis
Authors: Roth L. E.
Published: May 2004

1. The cell membrane of the spermatid of the grasshopper Melanoplus differentialis is shown to be composed of a double-layered membrane 10 mµ thick. Closely applied to this is an additional outer covering 25 to 35 mµ thick which has a regular geometrical pattern.

2. Models of cell membrane structure are discussed briefly. It is suggested that the pattern results from preferential adsorption of material onto a particular component of the double-layered membrane.
ELECTRON MICROSCOPE STUDIES OF CRYSTAL-COLLAGEN RELATIONSHIPS IN BONE
Authors: Sheldon Huntington , Robinson Robert A.
Published: May 2004

Crystals are seen occasionally within the diameter of transversely sectioned collagen fibrils near the calcification front of newly formed bone.
ARCHITECTURE AND NERVE SUPPLY OF MAMMALIAN SMOOTH MUSCLE TISSUE
Authors: Caesar Rudolf , Edwards George A. , Ruska Helmut
Published: May 2004

Smooth muscle tissue from mouse urinary bladder, uterus, and gall bladder has been studied by means of the electron microscope. The smooth muscle cells are distinctly and completely separated from each other by a cytolemma comparable to the sarcolemma of striated muscle. The tissue is thus cellular and not syncytial. With this evidence, supported by electron microscopy of other tissues, we question the existence of true syncytia in animal tissues. Individual cell membranes necessary for the electrophysiologic events exist in smooth muscle, and its nerve and conduction in a tissue such as uterus or bladder can occur at the cellular level as well as at the tissue area level.

The smooth muscle cell contains myofilaments, nucleus, endoplasmic reticulum, mitochondria, Golgi complex, centrosome, and pinocytotic vesicles. These structures are described in some detail, and their probable interrelations and functions are discussed.

The autonomic nerves innervating smooth muscle cells are composed of axons and lemnoblasts. The axon is suspended by the mesaxon formed by the infolded plasma membrane of the lemnoblast. The respective plasma membranes separate axon and lemnoblast from each other and from surrounding muscle cells. The axons of autonomic nerves never penetrate the plasma membrane of the muscle cell, but pass or intrude into muscle cell pockets, forming a contact between axonal plasma membrane and smooth muscle plasma membrane. The lemnoblast shows well developed endoplasmic reticulum with Palade granules, mitochondria, and a long, elliptical nucleus. The axon contains neurofilaments, mitochondria, and synaptic vesicles; the quantity of the latter two being significantly greater in the periphery of lemnoblasts and near axon-muscle contact regions. We regard the contact regions as the synapses between the autonomic nerves and the smooth muscle cells.
STUDIES ON THE BIOSYNTHESIS OF COLLAGEN
Authors: Jackson Sylvia Fitton , Smith R. H.
Published: May 2004

1. A tissue culture method was devised in which suspensions of osteoblasts, obtained directly from frontal bones of fowl embryos, were grown in a fluid, fibrin-free medium.

2. Maximum growth of the tissue, as measured by dry weight, with the formation of collagen protein, based on the estimation of hydroxyproline, was obtained in periods of up to 6 days.

3. Appreciable amounts of protein-bound hydroxyproline were formed during the first 24 hour growth period, but electron microscopy of portions of the same cultures failed to demonstrate the presence of any typical collagen fibrils.

4. The subsequent formation of many characteristic collagen fibrils was not associated with a significant rise in the mean hydroxyproline content of the tissue.

5. The cytoplasmic granules of the osteoblasts stained intensely with the P.A.S. technique when the collagen fibrils were being formed.

6. It is suggested that collagen-forming cells synthesise and secrete a hydroxyproline-rich precursor of protein or large peptide nature, which subsequently becomes directly transformed into typical collagen fibrils.
STUDIES ON THE BIOSYNTHESIS OF COLLAGEN
Authors: Smith R. H. , Jackson Sylvia Fitton
Published: May 2004

1. Fowl osteoblasts grown in bulk tissue cultures in the presence of 14C-(L)-proline incorporated this amino acid into peptide linkage. A significant amount of the incorporated radioactivity was found in the hydroxyproline, glutamic acid, and aspartic acid fractions of the cultures.

2. The rate of formation of protein-bound 14C-hydroxyproline from 14C-(L)-proline was maximal in cultures grown for 15 hours and fell exponentially with the increasing age of the cultures.

3. 14C-(L)-glutamic acid was incorporated by the osteoblast cultures, but no significant amount was converted to hydroxyproline.
THE ULTRASTRUCTURE OF THE VITELLINE BODY IN THE OOCYTE OF THE SPIDER TEGENARIA PARIETINA
Authors: André Jean , Rouiller Charles
Published: May 2004

The vitelline body in the mature oocyte of the spider Tegenaria parietina is composed of 4 different zones.

1. The central zone contains granular areas, vesicles, and a few lamellae.

2. The lamellar zone consists of numerous concentric lamellae. These sheets, 45 A in thickness, are stacked in groups. The fine structure and the regular arrangement recall those of myelin sheets, retinal rods, and chloroplasts. Between the stacks of lamellae, finely granular masses and various vesicles are to be found.

3. The "zone of transition" consists of a finely granular substance accumulated in abundant masses. This substance is composed of very closely packed granules about 50 to 60 A in diameter. Very often, near the lamellae, the granules show alignment giving a gradual transition from grains to lamellae.

4. The vesicular zone contains ergastoplasm, dense particles, mitochondria, and Golgi material. It is suggested that the peculiar ultrastructure of these cytoplasmic components may be related to an intense metabolic activity.
SITES OF GLYCOGEN SYNTHESIS IN RAT LIVER CELLS AS SHOWN BY ELECTRON MICROSCOPE RADIOAUTOGRAPHY AFTER ADMINISTRATION OF GLUCOSE-H3
Authors: Coimbra Antonio , Leblond C. P.
Published: May 2004

Glycogen synthesis was investigated by giving tritium (H3)-labeled glucose with carrier to fasted rats in vivo or incubating liver slices from fasted rats in vitro using a glucose-H3-containing medium. After 15 min or 1 hr, pieces of liver were fixed and radioautographed for light and electron microscopy. In vivo and in vitro, radioautographic reactions appeared over "glycogen areas" and over zones transitional between these areas and ergastoplasm. Treatment of sections by alpha amylase removed all but about 5% of the radioactivity, so that about 95% of it consisted of glycogen (synthesized during the 15 min or 1 hr elapsing after administration of glucose-H3). Within glycogen areas and transitional zones, most silver grains were over or very close to glycogen granules and smooth (or partly smooth) vesicles. Presumably, much of the label was added onto growing glycogen granules, in accord with the biochemical view that glycogen may serve as substrate for further glycogen synthesis. The few silver grains located far from glycogen granules—15% at the 15 min interval in vivo—approximated smooth (or partly smooth) vesicles of endoplasmic reticulum. This observation raised the possibility that smooth membranes play a role in glucose uptake at an early stage in de novo formation of glycogen granules.
AN ANALYSIS OF DNA LOSS AND SYNTHESIS IN THE RAT ADRENAL MEDULLA NUCLEI UPON COLD STIMULATION
Authors: Viola-Magni Maria Pia
Published: May 2004

The peculiar changes previously observed in DNA content of rat adrenal medulla cell nuclei upon intermittent cold exposure (15 hr at +4°C followed by 9 hr at room temperature) have been further studied with the aid of Feulgen histophotometry and H3-thymidine radioautography. The amount of DNA decreases progressively with increasing length of cold exposure until 300 hr (-32%). Later a rapid change takes place, whereby DNA content per nucleus returns to values which are slightly, but consistently lower than normal. At termination of a period of cumulative exposure to cold, an analysis of a whole-day experimental cycle shows that the DNA decrease is due to loss of DNA during cold exposure and that DNA synthesis occurs upon return to room temperature. The balance between these two processes can be divided into three stages: (a) loss of DNA up to 300 hr of cumulative cold exposure; (b) marked increase in DNA by 350 hr; (c) oscillation around zero or slightly negative at 400 hr and beyond. These variations are due to: (1) the extension of DNA synthesis into the period of cold exposure as clearly demonstrated by radioautography (stage b), and (2) a later still greater DNA loss (stage c) which partly offsets the increased synthesis. A complex pattern of adaptation of the adrenal medulla cells, as regards DNA content, to the repetitive cold stimulus is thus demonstrated.
SOME OBSERVATIONS ON THE FINE STRUCTURE OF THE LUTEIN CELLS OF X-IRRADIATED RAT OVARY
Authors: Flaks Bojan , Bresloff Paul
Published: May 2004

The ovaries of 10- to 13-week-old rats were exteriorized and irradiated with sterilizing doses of X-rays. Following treatment, the animals entered a phase of constant vaginal cornification. Animals were killed 8 to 12 wk after the onset of this phase, and their ovaries were prepared for electron microscopy. Tissue was fixed in glutaraldehyde, postfixed in osmium tetroxide (Millonig's, phosphate-buffered), and embedded in Epon. Lutein cells from these ovaries were compared with those from sham-irradiated controls. The cytoplasm of lutein cells from experimental animals was characterized by an increase in the amount of agranular endoplasmic reticulum and by an increase in the number of mitochondria. These mitochondria are more variable in external form and often possess increased numbers of villiform cristae. Other features noted were a decrease in the amount of cytoplasmic lipid granules and an increase in cell size and surface irregularity. The significance of the morphological findings is discussed in relation to ovarian hormone production in animals sterilized by X-irradiation.
ULTRASTRUCTURAL BASES FOR METABOLICALLY LINKED MECHANICAL ACTIVITY IN MITOCHONDRIA
Authors: Hackenbrock Charles R.
Published: May 2004

By means of a new "quick-sampling" method, micropellets of mouse liver mitochondria were rapidly prepared for electron microscopy during the recording of steady state metabolism. Reversible ultrastructural changes were found to accompany change in metabolic steady states. The most dramatic reversible ultrastructural change occurs when ADP is added to systems in which only phosphate acceptor is deficient, i.e., during the State IV to State III transition as defined by Chance and Williams. After 15 min in State IV, mitochondria display an "orthodox" ultrastructural appearance as is usually observed after fixation within intact tissue. On transition to State III, a dramatic change in the manner of folding of the inner membrane takes place. In addition, the electron opacity of the matrix increases as the volume of the matrix decreases, but total mitochondrial volume does not appear to change during this transition. This conformation is called "condensed." Isolated mitochondria were found to oscillate between the orthodox and condensed conformations during reversible transitions between State III and State IV. Various significant ultrastructural changes in mitochondria also occur during transitions in other functional states, e.g., when substrate or substrate and acceptor is made limiting. Internal structural flexibility is discussed with respect to structural and functional integrity of isolated mitochondria. Reversible changes in the manner of folding of the inner membrane and in the manner of packing of small granules in the matrix as respiration is activated by ADP represent an ultrastructural basis for metabolically linked mechanical activity in tightly coupled mitochondria.
THE FINE STRUCTURE OF THE EXOERYTHROCYTIC STAGES OF PLASMODIUM FALLAX
Authors: Hepler Peter K. , Huff Clay G. , Sprinz Helmuth
Published: May 2004

The fine structure of the exoerythrocytic cycle of an avian malarial parasite, Plasmodium fallax, has been analyzed using preparations grown in a tissue culture system derived from embryonic turkey brain cells which were fixed in glutaraldehyde-OsO4. The mature merozoite, an elongated cell 3- to 4-µ long and 1- to 2-µ wide, is ensheathed in a complex double-layered pellicle. The anterior end consists of a conoid, from which emanate two lobed paired organelles and several closely associated dense bodies. A nucleus is situated in the mid portion of the cell, while a single mitochondrion wrapped around a spherical body is found in the posterior end. On the pellicle of the merozoite near the nucleus a cytostomal cavity, 80 to 100 mµ in diameter, is located. Based on changes in fine structure, the subsequent sequence of development is divided into three phases: first, the dedifferentiation phase, in which the merozoite loses many complex structures, i.e. the conoid, paired organelles, dense bodies, spherical body, and the thick inner layers of the pellicle, and transforms into a trophozoite; second, the growth phase, which consists of many nuclear divisions as well as parallel increases in mitochondria, endoplasmic reticulum, and ribosomes; and third, the redifferentiation and cytoplasmic schizogony phase, in which the specialized organelles reappear as the new merozoites bud off from the mother schizont.
A MELTING POINT FOR THE BIREFRINGENT COMPONENT OF MUSCLE
Authors: Aronson John F.
Published: May 2004

The A filament of the striated muscle sarcomere is an ordered aggregate of one or a few species of proteins. Ordering of these filaments into a parallel array is the basis of birefringence in the A region, and loss of birefringence is therefore a measure of decreased order. Heating caused a large decrease in the birefringence of glycerinated rabbit psoas muscle fibers over a narrow temperature range (∼3°C) and a large decrease in both the birefringence and optical density of the A region of Drosophila melanogaster fibrils. These changes were interpreted as a loss of A filament structure and were used to define a transition temperature (Ttr) as a measure of the stability of the A region. Since the transition temperature was sensitive to pH, ionic strength, and urea, solvent conditions which often affect protein structure, it is an experimentally useful indicator for factors affecting the structure of the A filament. Fibers from glycerinated frog muscle were less stable over a wide pH range than fibers from glycerinated rabbit muscle, a fact which demonstrates a species difference in structure. Glycerinated rabbit fibrils heated to 70°C shortened to about 40% of their initial length. The extent of shortening was not correlated with the loss of birefringence, and phase-contrast microscopy showed that this shortening occurred in the I region as well as in the A region. This response may be useful for studying the I filament and actin in much the same way that the decrease in birefringence was used for studying the A filament and myosin. The observations presented show that some properties of muscle proteins can be studied essentially in situ without the necessity of first dispersing the structure in solutions of high or low ionic strength.
DISTRIBUTION OF NEWLY SYNTHESIZED AMYLASE IN MICROSOMAL SUBFRACTIONS OF GUINEA PIG PANCREAS
Authors: Siekevitz P. , Palade G. E.
Published: May 2004

Amylase distribution was studied in guinea pig pancreas microsomes fractionated by centrifuging, for 2 hr at 57,000 g in a linear 10 to 30% sucrose gradient, a resuspended high speed pellet obtained after treating microsomes with 0.04% deoxycholate (DOC).1 Amylase appeared in the following positions in the gradient: (a) a light region which contained ∼35% of total enzymic activity and which coincided with a monomeric ribosome peak; (b) a heavy region which contained ∼10% of enzymic activity in a sharp peak but which had very little accompanying OD260 absorption; (c) a pellet at the bottom of the centrifuge tube which contained ∼20% of the enzymic activity. After 5 to 20 min' in vivo labeling with leucine-1-C14, radioactive amylase was solubilized from these three fractions by a combined DOC-spermine treatment and purified by precipitation with glycogen, according to Loyter and Schramm. In all cases, the amylase found in the pellet had five to ten times the specific activity (CPM/enzymic activity) of the amylase found in the light or heavy regions of the gradient. The specific radioactivity (CPM/mg protein) of the proteins or peptides not extracted by DOC-spermine was similar for all three fractions. Hypotonic treatment of the fractions solubilized ∼80% of the total amylase in the fraction from the heavy region of the gradient, but only ∼20% of the amylase in the monomer or pellet fraction. Electron microscope observation indicates that the monomer region of the gradient contained only ribosomes, that the heavy region of the gradient contained small vesicles with relatively few attached ribosomes, and that the pellet was composed mostly of intact or ruptured microsomes with ribosomes still attached to their membranes. It is concluded from the above, and from other evidence, that most of the amylase activity in the monomer region is due to old, adsorbed enzyme; in the heavy region mostly to enzyme already inside microsomal vesicles; and in the pellet to a mixture of newly synthesized and old amylase still attached to ribosomes. Furthermore, the ribosomes with nascent, finished protein still bound to them are more firmly attached to the membranes than are ribosomes devoid of nascent protein.
AN INDIRECT METHOD TO ASSAY FOR MITOTIC CENTERS IN SAND DOLLAR (DENDRASTER EXCENTRICUS) EGGS
Authors: Went Hans A.
Published: May 2004

It is possible consistently to induce sea urchin and sand dollar eggs to cleave directly from one cell into four cells. This is done by exposing the fertilized eggs to benzimidazole for 20 to 30 min beginning about early metaphase. The mitotic apparatus regresses, the cells do not cleave, and shortly after they are returned to normal sea water an early-prophase-appearing nucleus is present in each cell. Each cell then organizes a tetrapolar tetrahedral mitotic apparatus de novo, instead of transforming a bipolar mitotic apparatus into a tetrapolar figure, and cleaves one-to-four. In another type of experiment, it appears that sand dollar eggs exposed to mercaptoethanol during the first period of mitotic center duplication have only half as many centers by first cleavage metaphase as the normal controls. This is consistent with an earlier report by Mazia et al (1960). Using this same experimental technique, it was demonstrated that benzimidazole, on the contrary, does not interfere with mitotic center duplication in sand dollar eggs. A labeling experiment demonstrated that benzimidazole does not interfere markedly with the normal pattern of incorporation of C14-thymidine into the DNA of sea urchin eggs. The data reported here suggest that judicious treatment of sand dollar eggs (and probably sea urchin eggs, too) with benzimidazole can induce the eggs to cleave into as many cells as there were mitotic centers sometime earlier, for example at early metaphase of the first cleavage division. This provides a very useful tool for studies on the process of mitotic center duplication.
ULTRASTRUCTURE OF THE CAROTID BODY
Authors: Biscoe T. J. , Stehbens W. E.
Published: May 2004

An electron microscope investigation was made of the carotid body in the cat and the rabbit. In thin-walled blood vessels the endothelium was fenestrated. Larger vessels were surrounded by a layer of smooth muscle fibers. Among the numerous blood vessels lay groups of cells of two types covered by basement membranes. Aggregates of Type I cells were invested by Type II cells, though occasionally cytoplasmic extensions were covered by basement membrane only. Type I cells contained many electron-opaque cored vesicles (350 to 1900 A in diameter) resembling those in endocrine secretory cells. Type II cells covered nerve endings terminating on Type I cells and enclosed nerve fibers in much the same manner as Schwann cells. The nerve endings contained numerous microvesicles (∼500 A in diameter), mitochondria, glycogen granules, and a few electron-opaque cored vesicles. Junctions between nerve endings and Type I cells were associated with regions of increased density in both intercellular spaces and the adjoining cytoplasm. Cilia of the 9 + 0 fibril pattern were observed in Type I and Type II cells and pericytes. Nonmyelinated nerve fibers, often containing microvesicles, mitochondria, and a few electron-opaque cored vesicles (650 to 1000 A in diameter) were present in Schwann cells, many of which were situated close to blood vessels Ganglion cells near the periphery of the gland, fibrocytes, and segments of unidentified cells were also seen. It was concluded that, according to present concepts of the structure of nerve endings, those endings related to Type I cells could be efferent or afferent.
PHYSICOCHEMICAL DIFFERENCES BETWEEN FRAGMENTS OF PLASMA MEMBRANE AND ENDOPLASMIC RETICULUM
Authors: Wallach Donald F. Hoelzl , Kamat Virendra B. , Gail Mitchell H.
Published: May 2004

Specific turbidities, densities, and refractive indices of fragments of plasma membrane (PM) and endoplasmic reticulum (ER) from Ehrlich ascites carcinoma have been measured. A spherical shell model of specified dimensions and refractive index was established for PM fragments. The ionic composition of the dispersion medium was varied systematically. Increases in Γ/2 caused increases in the turbidity of both PM and ER suspensions, the greatest effects being observed with Ca2+ and Mg2+. In the case of PM this effect is attributable mainly to aggregation, whereas "structural" changes account for most of the turbidity increase with ER. The pH was also varied systematically to obtain pH- density and turbidity profiles and to establish the isoelectric pH of the two membrane types (PM—3.6; ER—4.35). Turbidity was maximum at "isoelectric" pH, which corresponds in each case to the region of minimum charge on the particle surfaces. Both PM and ER show large increases of density at the "isoelectric" pH, but only ER shows substantial structurally based turbidity increase under these conditions. Both PM and ER show operation of electrostatic attractions near "isoelectric" pH. PM has been shown to have ionically distinctive inner and outer surfaces while ER shows no such dissymmetry. The necessary theoretical background for interpretation of turbidity and density measurements is included, as well as a discussion of the limitations of our conclusions and the biological importance of our results.
ACTIVE TRANSPORT BY THE CECROPIA MIDGUT
Authors: Anderson Everett , Harvey William R.
Published: May 2004

A morphological basis for transcellular potassium transport in the midgut of the mature fifth instar larvae of Hyalophora cecropia has been established through studies with the light and electron microscopes. The single-layered epithelium consists of two distinct cell types, the columnar cell and the goblet cell. No regenerative cells are present. Both columnar and goblet cells rest on a well developed basement lamina. The basal portion of the columnar cell is incompletely divided into compartments by deep infoldings of the plasma membrane, whereas the apical end consists of numerous cytoplasmic projections, each of which is covered with a fine fuzzy or filamentous material. The cytoplasm of this cell contains large amounts of rough endoplasmic reticulum, microtubules, and mitochondria. In the basal region of the cell the mitochondria are oriented parallel to the long axes of the folded plasma-lemma, but in the intermediate and apical portions they are randomly scattered within the cytoplasmic matrix. Compared to the columnar cell, the goblet cell has relatively little endoplasmic reticulum. On the other hand, the plications of the plasma membrane of the goblet cell greatly exceed those of the columnar cell. One can distinguish at least four characteristic types of folding: (a) basal podocytelike extensions, (b) lateral evaginations, (c) apical microvilli, and (d) specialized cytoplasmic projections which line the goblet chamber. Apically, the projections are large and branch to form villus-like units, whereas in the major portion of the cavity each projection appears to contain an elongate mitochondrion. Junctional complexes of similar kind and position appear between neighboring columnar cells and between adjacent columnar and goblet cells as follows: a zonula adherens is found near the luminal surface and is followed by one or more zonulae occludentes. The morphological data obtained in this study and the physiological information on ion transport through the midgut epithelium have encouraged us to suggest that the goblet cell may be the principal unit of active potassium transport from the hemolymph to the lumen of the midgut. We have postulated that ion accumulation by mitochondria in close association with plicated plasma membranes may play a role in the active movement of potassium across the midgut.
AN ELECTRON MICROSCOPE STUDY OF VITALLY STAINED SINGLE CELLS IRRADIATED WITH A RUBY LASER MICROBEAM
Authors: Storb Rainer , Amy Robert L. , Wertz Richard K. , Fauconnier Bernard , Bessis Marcel
Published: May 2004

An electron microscope study has been made of vitally stained single cells whose cytoplasm has been subjected to a localized ruby laser microbeam. Light and moderate laser absorption (the resultant of stain concentration and laser energy density) produced restricted selective damage of mitochondria in cells stained with Janus green B; heavy laser absorption resulted in mitochondrial damage, as well as in nonselective interaction with other cell structures. With four other basic vital stains, the polysomes, ergastoplasm, mitochondria and other organelles at the irradiated site were uniformly damaged. Unstained cells showed no morphological alterations. With light primary damage (that restricted to the irradiation site), no secondary effects of the incident radiation were observed. With moderate primary damage, however, secondary damage of the mitochondria in the unirradiated cell portions was produced, which was reversible within 4 hr after irradiation. Heavy primary lesions caused severe secondary alteration of all cell structures that was irreversible and cell death occurred within 2 hr. Surviving cells examined 24 hr after light and moderate irradiation could not be distinguished from unirradiated controls. The possible mechanisms involved in the production of laser-induced cellular alterations are discussed.
THE STRANDEDNESS OF MEIOTIC CHROMOSOMES FROM ONCOPELTUS
Authors: Wolfe Stephen L. , Hewitt Godfrey M.
Published: May 2004

Meiotic chromosomes were isolated from male Oncopeltus fasciatus by dissecting the testes under insect Ringer's solution and spreading the living cells on the Langmuir trough. After being dried by the critical point method, preparations were examined under the electron microscope. Chromosomes at all stages of prophase prove to be multistranded. A significant increase in the number of parallel 250 A fibers in the chromosomes occurs between zygotene and diakinesis. Parallel folding, rather than true multistrandedness, is interpreted as the mechanism responsible for this observed increase in multistrandedness. It has not been possible to determine whether the multistrandedness observed at leptotene represents true multistrandedness or is the result of parallel folding. Apparent multistrandedness is lost at metaphase when the 250 A fibers of the chromosomes become coiled more tightly. In preparations isolated by these methods, no structures other than the 250 A chromosome fibers are visible in the chromomeres, which appear as regionally coiled or folded areas of the fibers along the arm of the chromosome.
DEVELOPMENT OF THE FLAGELLAR APPARATUS OF NAEGLERIA
Authors: Dingle Allan D. , Fulton Chandler
Published: May 2004

Flagellates of Naegleria gruberi have an interconnected flagellar apparatus consisting of nucleus, rhizoplast and accessory filaments, basal bodies, and flagella. The structures of these components have been found to be similar to those in other flagellates. The development of methods for obtaining the relatively synchronous transformation of populations of Naegleria amebae into flagellates has permitted a study of the development of the flagellar apparatus. No indications of rhizoplast, basal body, or flagellum structures could be detected in amebae. A basal body appears and assumes a position at the cell surface with its filaments perpendicular to the cell membrane. Axoneme filaments extend from the basal body filaments into a progressive evagination of the cell membrane which becomes the flagellum sheath. Continued elongation of the axoneme filaments leads to differentiation of a fully formed flagellum with a typical "9 + 2" organization, within 10 min after the appearance of basal bodies.
RNA TRANSPORT FROM NUCLEUS TO CYTOPLASM IN CHIRONOMUS SALIVARY GLANDS
Authors: Stevens Barbara J. , Swift Hewson
Published: May 2004

The fine structure and cytochemistry of the extremely large RNA puffs, or Balbiani rings, in salivary gland nuclei of midge, Chironomus thummi, larvae have been investigated. The Balbiani rings are composed of a diffuse mass of electron-opaque 400 to 500 A granules, short threads about 180 to 220 A in diameter and associated fine chromatin fibrils. These components appear to be organized into brushlike elements which form the ring. Electron microscope cytochemistry has shown that the granules and short threads contain RNA. After ribonuclease digestion, only 50 to 100 A chromatin fibrils were apparent in the Balbiani ring, and the granules were no longer demonstrable. Deoxyribonuclease digestion had no apparent effect on these structures. Observations indicate that the granules are formed from the short threads and released into the nucleoplasm in which they are evenly distributed. At the nuclear envelope, many granules have been observed partially or completely within the nuclear pores. These granules become elongated and are shown to penetrate the center of the pore in a rodlike form, about 200 A in diameter. The Balbiani ring granules are not normally visible within the cytoplasm adjacent to the nuclear envelope, but have been rarely found in this region. It is suggested that the granules represent the product of the Balbiani ring, possibly a messenger RNA bound to protein, and that they regularly pass into the cytoplasm through a narrow central channel in the pores of the nuclear envelope.
THYMIDINE TRIPHOSPHATE SYNTHESIS IN TETRAHYMENA
Authors: Shoup G. D. , Prescott D. M. , Wykes J. R.
Published: May 2004

The amount of thymidine-H3 converted to thymidine-H3 monophosphate in 30 min formed the basis for assays of thymidine kinase in cell extracts from Tetrahymena pyriformis. The optimal concentration of adenosine triphosphate is lower than that required by other cell types. Thymidine triphosphate does not exercise any feedback control of the enzyme. Other deoxyprimidine nucleotides were tested, but these also failed to exhibit any feedback inhibition. At suboptimal adenosine triphosphate levels, thymidine triphosphate and other deoxypyrimidine nucleotides stimulate the reaction, suggesting that these nucleotides may act either directly or indirectly as phosphate donors in the crude enzyme preparations. This possibility was affirmed when thymidine triphosphate and deoxycytidine triphosphate were shown to be capable of limited phosphorylation of thymidine. Comparison of enzymatic activities in logarithmically growing culture and stationary phase culture, in which nuclear DNA synthesis has virtually ceased, reveals no change in enzymatic activity. The results suggest that thymidine kinase is a constitutive enzyme in Tetrahymena.
LYSOSOME FUNCTION IN THE REGULATION OF THE SECRETORY PROCESS IN CELLS OF THE ANTERIOR PITUITARY GLAND
Authors: Smith Robert E. , Farquhar Marilyn G.
Published: May 2004

The nature and content of lytic bodies and the localization of acid phosphatase (AcPase) activity were investigated in mammotrophic hormone-producing cells (MT) from rat anterior pituitary glands. MT were examined from lactating rats in which secretion of MTH1 was high and from postlactating rats in which MTH secretion was suppressed by removing the suckling young. MT from lactating animals contained abundant stacks of rough-surfaced ER, a large Golgi complex with many forming secretory granules, and a few lytic bodies, primarily multivesicular bodies and dense bodies. MT from postlactating animals, sacrificed at selected intervals up to 96 hr after separation from their suckling young, showed (a) progressive involution of the protein synthetic apparatus with sequestration of ER and ribosomes in autophagic vacuoles, and (b) incorporation of secretory granules into multivesicular and dense bodies. The content of mature granules typically was incorporated into dense bodies whereas that of immature granules found its way preferentially into multivesicular bodies. The secretory granules and cytoplasmic constituents segregated within lytic bodies were progressively degraded over a period of 24 to 72 hr to yield a common residual body, the vacuolated dense body. In MT from lactating animals, AcPase reaction product was found in lytic bodies, and in several other sites not usually considered to be lysosomal in nature, i.e., inner Golgi cisterna and associated vesicles, and around most of the immature, and some of the mature secretory granules. In MT from postlactating animals, AcPase was concentrated in lytic bodies; reaction product and incorporated secretory granules were frequently recognizable within the same multivesicular or dense body which could therefore be identified as "autolysosomes" connected with the digestion of endogenous materials. Several possible explanations for the occurrence of AcPase in nonlysosomal sites are discussed. From the findings it is concluded that, in secretory cells, lysosomes function in the regulation of the secretory process by providing a mechanism which takes care of overproduction of secretory products.
THE STRUCTURE OF EOSINOPHIL LEUKOCYTE GRANULES IN RODENTS AND IN MAN
Authors: Miller Fritz , de Harven Etienne , Palade George E.
Published: May 2004

The structure of the specific granules of eosinophil leukocytes has been studied by electron microscopy in sections of tissues, buffy coats, and sediments of peritoneal washings of rats, mice, guinea pigs, and men. The core of eosinophil granules is a crystal which has a cubic lattice with a repeat of ∼30 A in rodents and ∼40 A in man. The chemical composition of the core is discussed in connection with recent cell fractionation studies, and the hypothesis that the core is a crystal of peroxidase is considered.