bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of D-[3H]cis-diltiazem binding to membrane fractions and specific binding of calcium channel blockers to isolated flagellar membranes of Chlamydomonas reinhardtii
Authors: Dolle R. , Nultsch W. 
Published: April 2021

ABSTRACT
Plasma membranes were separated from the intracellular membranes by using an aqueous two-polymer phase system. D-[3H]cis-diltiazem was employed to characterize benzothiazepine-selective receptors in these different membrane fractions of Chlamydomonas reinhardtii. The separation revealed that one type of binding site with higher affinity (KD = 33 nM) can be attributed to the intracellular membrane fraction and a second type with lower affinity (KD = 313nM) to the plasma membrane fraction. The apparent dissociation constants determined from the association and dissociation rate constants in kinetic experiments are comparable to those determined by saturation experiments. The maximum numbers of binding sites of the intracellular mem-brane fraction and the plasma membrane fraction are Bmax = 6·4pmolmg-1 protein and Bmax= 19pmolmg-1 protein, respectively. D-[3H]cis-diltiazem binding is inhibited by (±)ver-apamil and calcium chloride in both fractions. Moreover, nifedipine stimulates D-[3H]cis-diltia-zem binding by the intracellular membrane fraction, but shows no effect on the plasma membrane fraction.
Ligand displacement binding studies with isolated flagella revealed the occurrence of a D-cis- diltiazem binding site with about the same affinity to this drug (KD = 400 nM) as the one found in the plasma membrane fraction. The maximum number of binding sites is 4-5pmolmg-1 protein. The apparent dissociation constants for specific [3H]nimodipine and [3H]verapamil binding to the flagella were calculated to be 8nM and 38 nM, respectively. The corresponding Bmax values are 345fmolmg-1 protein and 1’Spmolmg-1 protein, respectively.
Metaphase position of an interchange quadrivalent of Allium triquetrum III. the expected distribution based on randomness
Authors: Rickards Geoffrey K. , Baker Wendy A. 
Published: April 2021

ABSTRACT
The position of an interchange quadrivalent at metaphase I of Allium triquetrum was modelled so as to simulate the original placement of the quadrivalent in the spindle and the preparation of linear spreads through squashing. In this way an expected distribution for the quadrivalent in linear spreads was generated. The procedure used polar views of metaphase I to which the quadrivalent was assigned pairs of positions normally occupied by bivalents. The positions of the bivalents and assigned quadrivalent were then projected into a linear array and analysed as ‘real’ data. Comparisons with observed distributions showed that a general bias in favour of marginal placement of the quadrivalent in the linear array is expected; and also showed that the quadrivalent is positioned non-randomly in the metaphase plate prior to slide preparation.
Phagosome formation in Paramecium:, Effects of solid particles
Authors: Fok Agnes K. , Sison Benjamin C. , Ueno Marilynn S. , Allen Richard D. 
Published: April 2021

ABSTRACT
Digestive vacuole (DV) formation in Paramecium can be separated into four steps: sequestration and recycling of the spent DV membrane, sweeping and concentrating of particles into the nascent DV, vacuole growth, and the release of the nascent DV. How the size, load and surface charge of solid particles affected formation and subsequently the digestive processes in log-phase cells were investigated. Pulsing cells continuously with beads resulted in an initial linear increase, followed by a steady state, of labelled DVs. Above a certain threshold concentration, the rate of formation and the size of the DVs formed (as well as the steady state) all increased with increasing bead load, so that for a 16-fold increase in bead load, a corresponding fourfold increase in the incorporation of the recycled membrane into the DVs was observed. The threshold values, which depended on the sensitivity of the technique used to score these DVs, were lowered as bead size increased. The steady state of labelled DVs was shown to correspond to a strict balance between the formation and defecation rates as shown by efflux measurements and pulse-chase protocols using two consecutive labels. The duration of the pulse required to reach these steady states was inversely proportional to the logarithm of the bead number at low bead loads but remained constant at higher bead loads. The formation rates and the DV size were similar when cells were pulsed with beads from 0·5 to 3 μm, but DV size increased using beads of 4·5 and 5·7 μm. The maximal bead size that could be ingested was − 10 μm. Beads with a positive surface charge reduced the formation rate as well as the DV size. These results show that: (1) under normal conditions particle concentration can determine the formation rate and the DV size; (2) paramecia can form DVs continuously without any detectable interruptions; and (3) the rate of defecation and thus the rate of recycling of spent DV membrane is dependent on the rate of DV formation.
Presence And Distribution Of Specific Prosome Antigens Change As A Function Of Embryonic Development And Tissue-Type Differentiation In Pleurodeles Waltl
Authors: Pal J. K. , Gounon P. , Grossi de SA M.-F. , Scherrer K. 
Published: April 2021

ABSTRACT
The prosomes, biochemically well characterized small RNA-protein complexes, found associated with mRNA in all eukaryotic cells tested, have been identified as maternal components in sea urchin and chick embryos. In this study, we investigated their presence and cytolocalization in the oocytes and embryos of Pleurodeles waltl by immunoblot analysis and immunofluorescence, using monoclonal antibodies prepared against duck prosome proteins. Of the four anti-bodies tested, three recognized the corresponding antigens in oocyte total protein extracts. Immuno-fluorescence analysis, using the three prosomal antibodies, demonstrated a drastic change in the localization of the prosome antigens, which changed from the cytoplasm to the nucleus during oogenesis. In the nucleus, in diplotene stages, prosomal antigens appeared to be associated with the lampbrush chromosomes and the nuclear matrix.
During embryogenesis, the subcellular distribution of the prosome antigens was a function of development and differentiation: in the cleavage stages up to the mid-blastula they were localized in the cytoplasm and on the plasma membrane, while in the late blastula, gastrula and neurula they were in the nucleus. Interestingly, one of the prosome antigens, p31K, was found to be in a different location in certain cells in the animal pole of the mid-blastula and was absent in the neural tissue in the neurula. In still later stages, in the free-swimming larva, all three antigens were localized in the cytoplasm, specifically in certain cell types in the epidermal tissues. Furthermore, they were sectorially distributed in the cytoplasm. These data taken together indicate the possible presence of tissue-type-specific prosome antigens in Pleurodeles. Differentiation-dependent subcellular localization of the prosome antigens suggests a cell-compartment-related multiple function of prosomes.
Variation In Thin Filament Size In The Skeletal Muscle Of The Frog
Authors: Corsi Andrea , Granata Anna Luisa , Vecchi Cesare , Strabbioli Rosanna , Re Lamberto 
Published: April 2021

ABSTRACT
The sartorius muscle of Rana esculenta was fixed and dehydrated by different methods and cross-sections of sarcomeres of different lengths were examined by electron microscopy. The area within the outlines of the thin filaments in negatives was measured using a high-resolution television system and a graphics tablet or by using a microdensitometer and computer processing the images with a density threshold above the background level.
In all specimens the area of the thin filaments in the I-bands was found to be larger than in the fizones of the A-bands where the thick and thin filaments interpenetrate. The difference was statistically significant and independent of the length of the sarcomere. The results are in agreement with previous observations in glycerol-extracted fibres. It is suggested that the change in size of the thin filaments might be accounted for by some interaction with the thick filaments.
The 3T3 cell cycle at low proliferation rates
Authors: Brooks Robert F. , Riddle Peter N. 
Published: April 2021

ABSTRACT
When the proliferation rate of Swiss 3T3 cells is decreased by limiting the availability of growth factors, cell cycle variability increases, as predicted by the transition probability model. Nevertheless, the transition probabilities would appear to play a relatively minor role in the regulation of proliferation rate. Instead, at least 40% of the increase in the average cycle time is brought about by an elongation of the minimum cycle time (i.e. the ‘deterministic’ part of the cycle). In addition, we have found that a substantial proportion of the cells (roughly 20%, in the present experiments, for doubling times of the order of 35–40 h) drop out of cycle in each generation, leading to a growth fraction of less than 1·0. The non-dividing cells, which we have previously shown to remain capable of division, would seem to support the existence of a Go state outside the normal cell cycle, and distinct from the indeter-minate states postulated by the transition probability model. Because of the generation of non-dividing cells at low proliferation rates, the log α and β plots (distributions of cycle times, and sibling cycle time differences, respectively) are markedly concave, with a continuously decreasing slope. The transition probabilities cannot therefore be estimated directly and it is impossible to determine the extent to which they contribute to the regulation of proliferation rate. Rather, our data suggest that the transition probabilities are not uniform throughout the population under these conditions, but vary substantially from cell to cell.
In addition to the changes in cell cycle kinetics, we also report an increased failure rate of cyto-kinesis, at low proliferation rates, leading initially to the appearance of binucleate cells. Such failures of cytokinesis may be responsible for the well-known rise in the incidence of binucleate and polyploid cells in the liver, with age.
In Situ Preparation Of The Nuclear Matrix Of Physarum Polycephalum: Ultrastructural And Biochemical Analysis Of Different Matrix Isolation Procedures
Authors: Waitz Werner , Loidl Peter 
Published: April 2021

ABSTRACT
A novel method for in situ preparation of nuclear matrix from whole plasmodia of Physarum polycephalum without isolation of nuclei is presented. Plasmodia are encapsulated in agarose beads and after solubilization of the cytoplasm the nuclear matrix is prepared. With this quick and easy technique nuclear matrix can be reproducibly prepared with perfect recovery. We compared the ultrastructural and biochemical properties of the matrix after three different matrix isolation procedures: preparation with high salt, ammonium sulphate and lithium diiodosalicylic acid. The results show that the ultrastructure and protein composition of the three types of matrix are very similar or even identical. We conclude that many of the conflicting results on nuclear matrix in the literature are due to perturbations of nuclear integrity during the isolation of nuclei. For this reason the new in situ method is an important approach in the standardization of nuclear matrix isolation.
Expression of a mutated ras gene in Dictyostelium discoideum alters the binding of cyclic AMP to its chemotactic receptor
Authors: Ludérus M. E. E. , Reymond C. D. , Van Haastert P. J. M. , Van Driel R. 
Published: April 2021

ABSTRACT
Dictyostelium discoideum cells contain a ras gene that codes for a polypeptide that is highly homologous to the human ras proteins. Extra copies of the wild-type gene or a gene carrying a missense mutation in codon 12 (ras-Glyl2 and ras-Thrl2, respectively) have been introduced into Dictyo-stelium cells by transformation.
We have investigated the properties of the chemotactic cell surface cyclic AMP receptor in crude membrane preparations of wild-type Dictyostelium cells and ras-Glyl2 and ras-Thrl2 transformants. In vitro, an ATP- and Ca2+-dependent reduction of the number of cyclic AMP receptors was observed in membranes from all three cell types. The number of available receptors was decreased maximally by about 50%. In the presence of ATP the half-maximal Ca2+ concentration required for this process was about 10−5M in wild-type and ras-Glyl2 membranes, and less than 10−7M in ras-Thrl2 membranes. Addition of GTP (but not GDP) or the phorbol ester PMA (phorbol-12-myristate-13-acetate) reduced the Ca2+ requirement of the process in wild-type and ras-Gly12 membranes to the physiological level of less than 10−7M. In membranes derived from ras-Thrl2 cells addition of GTP or PMA had no effect.
The results indicate that D. discoideum cells contain a cyclic AMP receptor-controlling pathway that can be activated in vitro and involves a GTP-binding protein and a Ca2+ plus ATP-dependent activity, possibly protein kinase C. It is concluded that the ras protein specifically inter-acts with this pathway; the pathway appears to be constitutively activated by the mutated ras gene product.
Cytotoxic effects of cisplatin, cis-dichlorodiammineplatinum(ll), on Tetrahymena
Authors: Nilsson Jytte R. 
Published: April 2021

ABSTRACT
A study was made of the effects of cisplatin, cis- dichlorodiammineplatinum(II) (5-250 mg 1−1), on the physiology and fine structure of Tetrahymena. The physiological effects observed were dose-dependent. Endocytosis was inhibited reversibly in all, but late in the high, concentrations. After an initial dose-related increase, due to division of cells most advanced in the cell cycle, proliferation ceased for at least two normal cell generations (6h) in 50 and 100 mg drug 1− 1, but for 24h in 250mgl−1, after which multiplication was resumed in a dose-dependent manner. Exposure to cisplatin resulted in the appearance of small, refractive granules and platinum (i.e. electron-dense material) accumulated in these granules. Fine structural observations of cells exposed to 250 mg drug I− 1 showed nucleolar fusion and appearance initially of lipid droplets, dense granules and autophagosomes. A time-dependent redistribution of cell organelles was revealed by morphometry; in particular, the mitochondria increased in number, but decreased in size. Moreover, after prolonged treatment (24 h) and without cell division, the inner mitochondrial membrane had diminished and the ratio of the inner to the outer mitochondrial membrane was only half of the value for control mitochondria. Concomitantly with this decrease, the cell content of ATP was reduced to a similar extent. The findings indicate a specific action of cisplatin on mitochondria, resembling that induced in Tetrahymena by chloramphenicol and methotrexate.
Molecular organization of cell-wall crystals from Chlamydomonas reinhardtii and Volvox carteri
Authors: Goodenough Ursula W. , Heuser John E. 
Published: April 2021

ABSTRACT
The extracellular matrices of Chlamydomonas reinhardtii and Volvox carteri contain homologous salt-extractable crystalline layers that will self-assemble in vitro. The organization of these crystals is examined using the quick-freeze deep-etch technique. In C. reinhardtii, the outer layer of the crystal is an open polygonal weave (W6B); this is shown to be constructed from regular overlapping associations between the fibrous hydroxyproline-rich glycoprotein GP1. The inner layer of the crystal (W6A) is shown to be a copolymer of GP2 and GP3. The bulky globular domains of these glycoproteins form the rows of granules seen on the upper and lower surfaces of W6A in both Chlamydomonas and Volvox, and their filamentous domains interact to form a dense meshwork.
The shape of cultured epithelial cells does not depend on the integrity of their microtubules
Authors: Middleton C. A. , Brown A. F. , Brown R. M. , Roberts D. J. H. 
Published: April 2021

ABSTRACT
Fibroblasts are thought to require an intact system of cytoplasmic microtubules in order both to adopt and to maintain a polarized morphology in culture, but whether the same is true for epithelial cells is not clear. We therefore compared the effects of the microtubule-disrupting drugs, colcemid and nocodazole, on the morphology of isolated embryonic chick heart fibroblasts (HF), corneal epithelial (CE) and epidermal epithelial (EE) cells. Immunofluorescence observations showed that all three cell types contained abundant microtubules when cultured in control medium and that these were absent from cells cultured in medium containing either colcemid or nocodazole. Qualitative observations suggested that these drugs inhibited the polarization of spreading HF but had no effect on the morphology of either of the epithelial cell types. We confirmed this observation quantitatively using two measures of cell shape, elongation and dispersion, both of which increase with increasing polarization. Our measurements show that microtubuledisrupting drugs significantly reduce both the elongation and dispersion of spreading HF but do not have a significant effect on either of these measures for the epithelial cell types.
We quantified in a similar way the effects of microtubule-disrupting drugs on the morphology of all three cell types that had previously spread in control medium. We found that transferring spread HF to colcemid-containing medium significantly reduced both the elongation and dispersion of these cells but that the same treatment had no effect on these measures for either of the epithelial cell types.
Our observations suggest that, unlike the fibroblasts, the epithelial cell types we have studied do not require microtubules either to adopt or to maintain a polarized morphology.
Mechanism of ca2+ inhibition of cytoplasmic streaming in lily pollen tubes
Authors: Kohno Tadashi , Shimmen Teruo 
Published: April 2021

ABSTRACT
Using a Ca2+ ionophore, A23187, the free Ca2+ concentration ([Ca2+]) in the cytoplasm of pollen tubes of Liliutn longiflorum was controlled from the cell exterior. At [Ca2+] higher than 1·0×10−5M (pCa5-0), cytoplasmic streaming was inhibited, and the inhibition was irreversible. The ATP content did not change, but actin filaments were fragmented and formed aggregates. A subsequent decrease in [Ca2+] almost stopped the progress of the actin filament fragmentation, but filamentous actin did not re-form from the fragmented actin. In a previous paper, we reported that pollen tube organelle movement along characean actin bundles was inhibited by Ca2+ at 10−sM levels and the inhibition was reversible. In the present study, the reversibility was also demonstrated using an in situ Ca2+ treatment. Organelles were isolated from pollen tubes that had been treated with high [Ca2+] and A23187. They moved along characean actin bundles in Ca2+-free medium.
It is concluded that Ca2+ inhibition of cytoplasmic streaming can be attributed to both inactivation of myosin and fragmentation of actin. The irreversibility of Ca2+ inhibition in situ is attributed to the irreversible fragmentation of actin filaments.
Chemical signal-response in diatoms of the genus Amphora
Authors: Cooksey Barbara , Cooksey Keith E. 
Published: April 2021

ABSTRACT
The marine diatom Ampbora coffeaeformis is positively chemotactic to glucose and sugars of similar structure. A free hydroxyl group is required at the 2-position of the ring; however, D-mannose (a toxic sugar) and L-glucose promote negative chemotaxis. Sugar metabolism is not necessary for a chemosen-sory response. When the direction of higher concentration in a D-glucose gradient is reversed, cells already orientated reverse their direction of movement. Pretreatment of diatoms with a uniform concentration of D-glucose before exposure to a concentration gradient eliminates the chemotactic response. When diatom cells attached to surfaces in the presence of 5 mM-Ca2+ are exposed to 0·25–0,625mM Ca2+, their motility drops rapidly. However, when this experiment is carried out in the presence of a uniform concentration of D-glucose or 3-O-methyl-D-glucose, motility is sustained for 25–30 min before falling. Speed of motility is also increased during this period. These results can be interpreted in terms of an agonist bindingsecretion coupling model for diatom chemotaxis.
Localization of calmodulin in the enterocyte of Necturus small intestine
Authors: Scully R. R. , Dedman J. R. , Schultz S. G. 
Published: April 2021

ABSTRACT
Calmodulin was localized in the small intestine of Necturus maculosa at both the light- and electron-microscopic levels utilizing an affinity-purified, monospecific antibody and immunoperoxidase cytochemistry. The microvilli and basolateral membranes of the epithelium were highly reactive, the cytoplasm was moderately reactive. Connective tissue, endothelia, and muscularis of the submucosa were also reactive. The mitochondrial matrix, nuclear envelope, and terminal web, and mucous granules of goblet cells were unreactive. Omission of the primary antibody, substitution of immunoglobulin not bound to the affinity column or inappropriate immunoglobulin (sheep anti-viral src product) for the primary antibody, caused no immunoreaction product to be formed.
Maintenance of multiplication rate stability by cell populations in the face of heterogeneity among individual cells
Authors: Grundel Ralph , Rubin Harry 
Published: April 2021

ABSTRACT
We addressed the question of how a population of cells can maintain a constant multiplication rate given the heterogeneity of its individual members. Using the NIH 3T3 line of mouse embryo cells, comparisons were made of multiplication rates between offspring subclones and the parental clones from which the subclones were derived. Parents at all levels of multiplication rate produced offspring with a wide range of multiplication rates. Offspring from parent cells with the highest growth rates rarely exceeded their parents in rate of multiplication. Offspring from slow-growing parents, however, often exceeded the parents.
It is concluded that the multiplication of NIH 3T3 populations represents constant diversification in multiplication rate: heterogeneous parents producing heterogeneous offspring. Population growth rates can remain stable because the fastest-growing parents generally produce offspring that multiply slower than the parents while the slowest parents often produce offspring that multiply faster than the parents.