bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchronized mammalian cell cultures. I. Cell replication cycle and macromolecular synthesis following brief colcemid arrest of mitosis
Authors: Stubblefield Elton , Klevecz Robert , Deaven Larry
Published: February 2005

Chinese hamster fibroblasts in monolayer cultures were synchronized by accumulating mitotic cells in the presence of Colcemid, removing the mitotic cells with a brief trypsin treatment, and growing them in medium lacking Colcemid. Such cultures grew normally and exhibited no significant deviations from control cultures in their mitotic interval, generation time, DNA synthesis kinetics, or proliferative capacity.

The macromolecular composition of 106 mitotic cells was chemically determined to be: DNA, 15 μg; RNA, 28 μg; and protein, 190 μg. In stock cultures, the corresponding values were about 60% to 70% of those for mitotic cells.

The kinetics of DNA, RNA, and protein synthesis were measured throughout a 12‐hour cell cycle by incorporation of tritiated precursors. DNA synthesis began two hours after, and continued until ten hours after Colcemid recovery, with 40 minute interruptions at five and eight hours. RNA synthesis commenced at one hour and continued linearly until the fifth hour, at which time the rate abruptly doubled. Protein synthesis began immediately after cell division (0.5 hour) and continued linearly until the sixth hour, at which time its rate also doubled.

The simplest interpretation of the data suggests that most of the DNA involved in transcription was replicated in the first third of the DNA synthesis period. Thereafter, the rates of RNA and protein synthesis increased because of the doubling of the active template population in each cell.
Dynamic adhesion and separation of cells in vitro II. Interactions of cells with hydrophilic and hydrophobic surfaces
Authors: Weiss Leonard , Blumenson Leslie E.
Published: February 2005

Experiments made on the passage of cells through untreated and siliconized glass beads, and on the adhesion and spread of cultured cells on glass and Teflon surfaces show that, in the absence of serum and in its presence in low concentrations, cell adhesion and spread is sensitive to substratum wettability. On the other hand, in the presence of 100% serum, no differences in adhesive parameters are detectable. It is concluded that arguments correlating cell adhesion to surface wettability, and, by inference, surface free energy, are unsubstantiated in 100% serum, which may well approximate to the in vivo situation.

The results also show no correlation between parameters of cell adhesion and cell separation, and thereby support the hypothesis that these are different processes.
Colony stimulating activity of serum from germfree normal and leukemic mice
Authors: Metcalf Donald , Foster Roger , Pollard Morris
Published: February 2005

Serum from germfree Swiss/HaM mice exhibited a reduced capacity to stimulate granulocytic and mononuclear cell colony formation by DBA/1 bone marrow cells in vitro when compared with serum from conventional Swiss/HaM mice. Sera from germfree preleukemic and leukemic AKR mice exhibited strong colony stimulating activity, indicating that the increased colony stimulating activity previously observed in the serum of conventional leukemic mice is not the consequence of bacterial or fungal infections supervening in leukemic animals with deficient immune responses.
Fluctuation of alkaline phosphatase activity in synchronized heteroploid cell cultures: Effects of prednisolone
Authors: Melnykovych George , Bishop Carole F. , Swayze Mary Ann B.
Published: February 2005

In two heteroploid cell lines synchronized with thymidine double block, activity of alkaline phosphatase decreased during the 12 hour period preceding mitotic peak. A return to high values was observed during the next 12 hours of synchronous cycle. Prednisolone (11β, 17α, 21‐trihydroxy‐1,4‐pregnadiene‐3,20‐dione), when added to such cell cultures increased alkaline phosphatase activity in one of the cell lines (Henle embryonic intestine) but had the opposite effect on another line (HeLa‐S3) in which the enzyme activity was decreased. Neither effect could be demonstrated if the hormone was added at the end of S phase or if cells were arrested in metaphase by vinblastine sulfate.
The influence of progressive growth on the specific catalase activity of human diploid cell strains. I. Effect of cellular genotype: Homozygous strains
Authors: Pan Yue‐Liang , Krooth Robert S.
Published: February 2005

The specific catalase activity of human diploid cell strains increases with progressive growth of the culture, and falls again following subculture. Although the increase is small, it is readily demonstrable, and is exponential with time.

The response of catalase activity to proggressive growth of the culture was studied in three abnormal human cell lines. A diploid cell strain, developed from a patient homozygous for the gene causing acatalasia I, had no detectable catalase activity throughout the life cycle of the culture. Another diploid cell strain, developed from a patient homozygous for the gene causing acatalasia II, had about 5% normal catalase activity, but the proportionate increase in specific activity as the culture grew was the same as for normal cells. Thus the mutation causing acatalasia II does not change the responsiveness of the cell in terms of catalase activity to progressive growth of the culture. The behavior of a heteroploid line was similar to that of the normal diploid strains, but when the growth of the heteroploid cultures reached a plateau, their population densities were four times higher than those of the diploid strains and they had about twice the specific catalase activity.
Hemopoietic progenitor cells of W anemic mice studied in vivo and in vitro
Authors: Bennett M. , Cudkowicz G. , Foster R. S. , Metcalf D.
Published: February 2005

The proliferation and differentiation of hemopoietic cells from genetically anemic Wv/Wx,W/Wv, and Wv/Wv mice, and from nonanemic carrier W/+, Wb/+, and Wv/+ mice have been evaluated in vivo by transplantation techniques and in vitro by the agar gel culture method. Marrow from anemic and carrier mice contained progenitor cells which were decreased in number and formed small, often rudimentary, colonies in the spleens of irradiated recipient mice. Proliferation and differentiation of both erythropoietic and leukopoietic progenitor cells were delayed and reduced, but erythropoiesis was more severely affected than leukopoiesis. The severity of the hemopoietic impairment was gene‐dose dependent. The W gene effect on leukopoietic progenitor cells was not secondary to anemia or to abnormal erythropoiesis.

The marrow cells of anemic and carrier mice which form colonies of granulocytic and mononuclear cells in vitro were neither decreased in number nor impaired in proliferation and differentiation. Hypertransfusion of red blood cells increased the frequency of in vitro colony‐forming cells, but not that of in vivo progenitor cells.

The data demonstrate that colony‐forming cells which proliferate in the agar gel cultures in vitro are distinct from the in vivo colony‐forming cells and suggest that the former are primitive members of the granulocytic cell line. Perhaps in vitro CFU are in an intermediate stage of differentiation between in vivo CFU and myeloblasts, analogous to that which has been suggested for the erythropoietin‐sensitive cell in the red cell series. W mutant alleles appear to act, therefore, at or very near the beginning of hemopoietic differentiation.
Analysis of growth factor gradients in hydra
Authors: Macklin Martin
Published: February 2005

Differential equations have been written and solved to describe the concentration gradients for the two hydra growth factors. The equations consider diffusion, catabolism and synthesis of the materials based primarily on the model of hydra growth described by A. L. Burnett. Concentration gradient profiles were obtained which correspond with the concentration gradients deduced from experimental evidence. It has also been possible to show that in areas of high mitotic rate, mitotic rate is related to the calculated concentration ratio of the two growth factors (stimulator/inhibitor). However, the correspondence of mitotic rate to growth factor concentration ratio does not hold for extreme values of the ratio indicating that very high and very low concentration ratios are not conductive to mitotic activity.
Cytological effects on Chinese hamster cells of synchronizing concentrations of hydroxyurea
Authors: Yu C. K. , Sinclair W. K.
Published: February 2005

The cytological effects of 2 mM hydroxyurea upon Chinese hamster cells at various phases of the cell cycle were examined. Cells in the G1, G2, or M phases of the generation cycle treated with hydroxyurea showed no chromosomal aberrations. Cell treated in S phase became moribund and eventually lysed. Some of these moribund S cells reached mitosis much later and were found to have chromatid aberrations. Cells in the log phase of growth, surviving exposure to 2 mM hydroxyurea for six hours, also showed no aberrations. Thus, viable (colony‐forming) cells, resulting from synchrony procedures with hydroxyurea are free of chromosomal aberrations.
Role of phospholipids in the aerobic endogenous metabolism of freshwater mussel spermatozoa
Authors: Higashi Satoru , Kawai Kiozo
Published: February 2005

Aerobic incubation of the spermatozoa of freshwater mussel (Hyriopsis schlegelii) caused a reduction in acyl‐ester content and a corresponding diminution in lipid‐phosphorus content. Anaerobic incubation also caused a reduction in acyl ester but a smaller reduction in lipid phosphorus, while it brought on an accumulation of free fatty acids. It was mainly palmitic and stearic acids which were accumulated during the anaerobic incubation, and they were preferentially metabolized during the aerobic incubation. Complex lipids from the spermatozoa consisted mainly of diacyl glycerophospholipids, in which phosphatidylethanolamine was predominant, followed by lecithin, while plasmalogen was a minor component. After aerobic incubation of the spermatozoa, there was a marked decrease in ethanolamine‐containing phospholipid fraction. However, no diminution was observed in the plasmalogen content. These results lead to the conclusion that mussel spermatozoa utilize as a primary energy source fatty acids which are derived from the breakdown of intracellular diacyl glycerophospholipids.
Interphase action of vinblastine and vincristine: Differences in their lethal action through the mitotic cycle of cultured mammalian cells
Authors: Madoc‐Jones H. , Mauro F.
Published: February 2005

Vinblastine and vincristine, agents which cause arrest of cells in mitosis, have been examined for their effect on the survival of synchonously growing HeLa and Chinese hamster cells. At concentrations higher than those sufficient to induce mitotic arrest, both agents were found to exert a differential lethal action depending upon the position of the cells in interphase. Cells exposed for a short time (3 hours) to 0.3 μg/ml of vinblastine are more sensitive in S and in late G1 than those in other parts of G1 or in G2. Cells exposed to vincristine (0.1 μ/ml) show only the S phase sensitivity. These difference reflect variations in the survival curves for the two drugs in different phases of the cycle. Cells exposed for a short time to lethal doses of either agent during the S phase proceed at a normal rate to mitosis where they are then arrested irreversibly. In addition, vinblastine causes an immediate interphase death by lysis of cells treated in late G1.
Effects of divalent cations on adhesiveness of rat polymorphonuclear neutrophils In vitro
Authors: Garvin James E.
Published: February 2005

Cell preparations rich in polymorphonuclear neutrophils (PMN) were obtained from peritoneal exudates of rats without the use of any anticoagulant. The adhesiveness of these PMN to glass bead columns coated with rat serum were studied quantitatively using suspending solutions free of added serum protein. A dependence of the PMN adhesiveness upon divalent cations was demonstrated. Added singly Mg2+, Ni2+, Zn2+, Co2+, Mn2+, Cu2+, or Cd2+ were found to be effective whereas Ca2+, Sr2+ and Ba2+ were ineffective. A possible auxilliary role for Ca2+ when added with Mg2+ is suggested by the data. The ineffectiveness of the ions Ca2+, Sr2+ and Ba2+ was shown by use of an ion electrode not to be due to the unavailability of the ionized species. Procedures are described for obtaining highly reproducible results with the Orion Divalent Cation Electrode. The ineffectiveness of the ions Ca2+, Sr2+ and Ba2+ were also shown not to be due to action as general protoplasmic poisons. The effective ions are distinguished from the ineffective ones by characteristic ranges of ionic radii, coordination number, second ionization potentials, electronegativities and affinity constants. Removal of components of complement from the cells by washing in 0.05 M EDTA, and heating all serum used for 30 minutes at 56°C had no significant effect on the adhesiveness of the PMN. A role for complement, therefore appears largely excluded.
The self renewal probability of hemopoietic stem cells
Authors: Vogel Helmut , Niewisch Helgard , Matioli Gastone
Published: February 2005

The probability of a colony which originated as a single stem cell to become extinct due to differentiation of all of its stem cells in any generation is closely connected to stem cell self renewal probability p. p can be determined from the coefficient of variation of the colony numbers received by reinjecting single colonies of the same age. Whole spleens containing a known average colony number can also be used with advantage for this purpose. The results of both procedures indicate a stem cell self renewal probability p =0.62 ± 0.04, which does not change significantly between the sixth and the fourteenth day of colony development, and an extinction probability ω = 0.63 ± 0.12.
Decreased neutrophils and megakaryocytes in anemic mice of genotype W/Wv
Authors: Chervenick Paul A. , Boggs Dane R.
Published: February 2005

The concentration of neutrophils and megakaryocytes was determined in the marrow of anemic mice of genotype W/Wv and their normal (+/+) litter mates. In all groups studied, the humerus of W/Wv mice contained significantly less neutrophils and megakaryocytes than did normal animals. Blood neutrophil concentration was less in all groups of W/Wv mice but in only one group which was the youngest group studied, did this value differ significantly from normal.

The blood and marrow neutrophil response to endotoxin was similar in W/Wv and “+/+” animals. This suggests that the neutrophilic system of W/Wv mice responds to this stimulus in a relatively normal manner, much as their erythroid system responds to hypoxia, and androgens.
Cell electrophoretic mobility and cationic flux
Authors: Weiss Leonard , Levinson Charles
Published: February 2005

The net negativity of the surfaces of Ehrlich ascites cells was reduced by treating them with either neuraminidase or ribonuclease. Neither enzyme treatment affected the Na+ or K+ content of the cells, before or after cooling at 4°C. Experiments with K42 revealed a reduction (9.5 to 17%) in unidirectional K+‐fluxes following incubation with neuraminidase, but no change after ribonuclease‐treatment. Our data suggest that surface anionic sites associated with RNA and sialic acid moieties are not of major quantitative importance in regulating either intracellular Na+ and K+ concentrations, or unidirectional transmembrane K+‐flux. Our results do not enable us to determine whether ion‐binding to anionic sites at the electro‐kinetic surface is not an essential prerequisite to transmembrane movement, or whether it is essential, but occurs through the 40% of cell surface net negativity which is unaffected by ribonuclease‐ and neuraminidase‐treatment.
Formation and properties of thin‐walled phospholipid vesicles
Authors: Reeves John P. , Dowben Robert M.
Published: February 2005

Large numbers of thin‐walled vesicles, 0.5 to 10 μ in diameter, can be formed by permitting a thinly spread layer of hydrated phospholipids to swell slowly in distilled water or an aqueous solution of nonelectrolytes. Electron micrographs and phospholipid analyses indicate that the walls consist of a single or a few bilayers. The vesicles can be centrifuged and resuspended in another medium, making them a useful system for studying permeability. The osmolarity of the solution in the interior of the vesicles can be estimated by immersion refractometry. The osmolarity of the internal aqueous phase is linearly related to the osmolarity of the external medium.
Phenylalanine hydroxylase activity in mammalian cells
Authors: Tourian Ara , Goddard Judy , Puck Theodore T.
Published: February 2005

Survey of twelve mouse tissues revealed the presence of appreciable phenylalanine hydroxylase activity in the pancreas and kidney as well as the liver but in no other of the tissues tested. Single cell suspensions of mouse liver were prepared by use of tetraphenylboron. The enzyme activity of such suspensions was much more stable than that of liver extracts, and permitted determination of the Michaelis‐Menten constant, the pseudo‐first order reaction velocity constant on a cell‐number basis, and the temperature coefficient and apparent activation energy of the enzyme activity. Possible applications of these methods to problems in cellular biology have been indicated.
A comparative study of the role of mitochondria and the sarcoplasmic reticulum in the uptake and release of Ca++ by the rat diaphragm
Authors: Carafoli Ernesto , Patriarca Pierluigi , Rossi Carlo Stefano
Published: February 2005

The respective importance of mitochondria and of sarcoplasmic reticulum in the uptake and maintenance of Ca++ by the isolated rat diaphragm has been compared. Diaphragms were incubated at 30° in conditions optimal for Ca++ uptake either by isolated mitochondria or by sarcoplasmic reticulum: more Ca++ was taken up from the “mitochondrial” medium. For maximal uptake, Pi and Mg++ were necessary; substitution of NaCl and KC1 with sucrose had no effect on the uptake. The uptake was markedly inhibited by uncouplers of oxidative phosphorylation, by respiratory inhibitors, and by lowering the temperature of the incubation medium to 0°; it was not affected by oligomycin, aurovertin, DCCD, nor by inhibitors of Ca++ transport in the isolated sarcoplasmic reticulum (ergotamine, ergobasinine, caffeine). The lack of effect of caffeine was not due to lack of penetration into the muscle. Permeability barriers for ergotamine and ergobasinine could not be excluded. The maintenance of Ca++ by the diaphragm was optimal in a medium contaming Pi and Mg++. Uncoupling agents and respiratory inhibitors accelerated the rate and extent of release of Ca++ by the diaphragm. Lowering the temperature of the incubation medium to 0°, or addition of oligomycin, aurovertin, DCCD, had no effect on the release. The release of Ca++ was also unaffected by ergotamine, ergobasinine, caffeine. The results suggest a role for mitochondria in the uptake and maintenance of Ca++ by the isolated diaphragm.
Purification and ultrastructural properties of the calcium accumulating membranes in isolated sarcoplasmic reticulum preparations from skeletal muscle
Authors: Greaser M. L. , Cassens R. G. , Hoekstra W. G. , Briskey E. J.
Published: February 2005

Sarcoplasmic reticulum fragments, prepared from skeletal muscle homogenates, were found to consist of two major types when examined after negative staining. One type possessed 90 Å subunits and was thought to be of mitochondrial origin. The other had 35 Å subunits and ws presumably derived from the sarcoplasmic reticulum. Only the latter type accumulated visible calcium oxalate deposits inside the vesicle when they were exposed to a medium containing ATP, MgCl2, K2C2O4 and CaCl2. The calcium oxalate loaded vesicles were strikingly angular in shape and did not have tails. The calcium oxalate loaded vesicles had identical membrane subunit arrangement to inactive companion membranes and nonincubated controls; this suggested that the membrane subunits were not the critical structural requirement for calcium transport. A method was described whereby the calcium accumulating membranes could be purified 3‐ to 4‐fold on the basis of the best previously used preparation procedures.
Physical separation of hemopoietic stem cells from cells forming colonies in culture
Authors: Worton R. G. , McCulloch E. A. , Till J. E.
Published: February 2005

Mouse bone marrow cells in suspension were separated into a number of fractions on the basis of cell density by equilibrium density gradient centrifugation, or on the basis of cell size by velocity sedimentation. After each type of separation, the cells from the various fractions were assayed for their ability to form macroscopic spleen colonies in irradiated recipient mice, and for their ability to form colonies in a cell culture system. The results from either separation technique demonstrate that cells in some fractions formed more colonies in vivo than in the culture system, while cells in other fractions formed more colonies in culture than in the spleen. The results of control experiments indicate that this separation of the two types of colony‐forming cells was not an artifact of the separation procedures. From these experiments it was concluded that the population of cells which form colonies in culture under the conditions used is not identical to the population of cells detected by the spleen colony assay.
Viability of human diploid cells as a function of in vitro age
Authors: Merz George S. , Ross John D.
Published: February 2005

The fraction of cell capable of division was determined for (1) population of the human diploid cell strains, WI38 after different numbers of subcultivations in vitro and (2) a single population of WI38 cells at intervals throughout its entire in vitro lifespan. In both cases the percentage of cells capable of division decreased with increasing age in tissue culture. The rate and the magnitude of the decrease is sufficient to account for the limited in vitro lifespan reported by other investigators. Furthermore, the decrease in the fraction of cells capable of division in similar in some respects of senescence among human populations.
Permeability and photoxidative damage of membrane enzymes
Authors: Duncan C. J. , Bowler K.
Published: February 2005

The pattern of photodynamic damage of pig erythrocyte and rat brain microsomal ATPases and erythrocyte acetylcholinesterases has been studied, using rose bengal as photosensitizer. Of these enzymes the Na+‐K+‐Mg2+‐ATPase, believed to be associated with active transport, is very much more sensitive to damage than are the Mg2+‐ATPase and the erythrocyte acetylcholinesterase. Earlier photoxidative studies of the haemolysis of erythrocytes have shown that ion movements occur in two phases which are dependent on the duration of exposure to light and it is suggested that these are correlated with the differential sensitivity of these membrane enzymes.

The ATPases of the brain microsomal preparation were more sensitive to photodynamic damage during preincubation at 0°C, i.e. in the absence of substrate. Raising the preincubation temperature to 37°C protected both enzymes, the inactivation of the Na+‐K+‐Mg2+‐ATPase being markedly reduced. The presence of substrate during pre‐incubation at 0°C also protects both enzymes, especially the Mg2+‐ATPase. These interacting effects of temperature and substrate are compared with the known different temperature sensitivities of these two enzymes.
A melanin‐dispersing effect of cyclic adenosine monophosphate on Fundulus melanophores
Authors: Novales R. R. , Fujii R.
Published: February 2005

Treatment of Fundulus melanophores with adenosine 3′,5′‐monophosphate (cyclic AMP) is followed by reversible melanin dispersion in these cells. Adenosine 3′‐monophosphate and adenosine 5′‐monophosphate both have a similar, but weaker dispersing action. In addition, adenosine 5′‐monophosphate also has a melanin aggregating effect. These results are interpreted to mean that nerve transmitters may act by controlling the level of cyclic AMP within the Fundulus melanophore.
Colony‐forming cells in organ cultures of embryonal liver
Authors: Latsinik Nataly V. , Luria Elen A. , Friedenstein Alexander J. , Samoylina Nina L. , Chertkov Iosiph L.
Published: February 2005

Livers from 17‐ to 20‐day CBA mouse embryos were maintained for three weeks in organ culture. During this period, hematopoiesis continued; morphologically recognizable cells were identified until day 24 and hematopoietic cells with colony forming ability were present until day 23. The method appears to hold promise for studies of hematopoietic differentiation in vitro.
Further studies on the biological properties of friend virus‐induced leukemic cells differentiating along the erythrocytic pathway
Authors: Rossi Giovanni B. , Friend Charlotte
Published: February 2005

When Friend virus‐induced leukemic cell lines were injected into irradiated hosts after the second radiation dose, the colony‐forming unit (CFU) in the recipient spleens per 104 cells was found to be 7‐fold higher than the CFU obtained when the second radiation dose had been given shortly after the inoculation of the cells. Serial passage of the cells from the spleen colonies to irradiated hosts resulted in a marked increase of the CFU value, indicating that this cell population was capable of both self‐replication and erythroid differentiation. The “f” fraction, which indicates the percentage of the inoculated cells that reach the spleen in the irradiated recipients, was found to be approximately 15%. If the highest CFU value obtained from serial colony‐to‐colony passages is corrected by this factor, a final cloning efficiency of about 18% is demonstrated.

Neither induced plethora nor the administration of erythropoietin (1 u/mouse/for 2 days) appeared to affect the spleen colony‐forming ability of the leukemic cells.

Erythroid differentiation is not detectable in the transplantable subcutaneous tumors which were used to initiate the tissue culture lines and which also are capable of inducing erythroid spleen clones in irradiated recipients. This lends support to the theory of the influence of “microenvironmental factors” on the fate of stem cells with potential for differentiation.
Selection of synchronous Chlorella cells by centrifugation to equilibrium in aqueous ficoll
Authors: Hopkins H. A. , Sitz T. O. , Schmidt R. R.
Published: February 2005

Synchronous daughter cells of Chlorella pyrenoidosa can be selected, on the basis of their unique density, from cultures growing in continuous light by centrifugation to equilibrium in aqueous Ficoll. The degree of synchrony, as judged from cell release data, is equivalent to or better than that obtained by intermittent‐illumination procedures.
The molecular biology of reovirus
Authors: Joklik Wolfgang K.
Published: February 2005

The genome of reoviruses consists of ten discrete segments of double‐stranded RNA. The molecular weight of three of these, the L segments, is about 2.7 × 106; of another three, the M segments, about 1.4 × 106; and of the remaining four, the S segments, 0.6–0.8 × 106. In addition, reovirions contain about 2,000 molecules of oligonucleotide from 2 to 20 nucleotides long, most of which are very rich in ademine.

The protein capsid of reovirions, which consists of an inner core and 92 outer shell capsomeres, is composed of seven species of polypeptides which also fall into three size classes. The size of six of these polypeptides is such that each accounts for the entire information content of one of the genome RNA segments.

Reovirus messenger RNA molecules are transcripts of all ten genome RNA segments. Transcription proceeds not only in vivo in the infected cell, but can also take place in vitro. It is then catalyzed by reovirus cores, the polypeptide composition of which is strikingly similar to that of E. coli DNA‐dependent RNA polymerase. Transcription both in vitro and in vivo is entirely asymmetric and is conservative with respect to template.

The patterns of transcription of the several reovirus genome RNA segments have been determined both in vitro and in vivo and the pattern of translation has been analyzed under in vivo conditions. The results suggest that transcription and especially translation are regulated within infected cells.
Influence of exogenous ions on the events of maturation in Rana pipiens oocytes
Authors: Ecker R. E. , Dennis Smith L.
Published: February 2005

Full‐grown ovarian oocytes removed from non‐hormone‐treated Rana pipiens females exhibit a low level of protein synthesis, the rate of which is dependent upon the ionic environment. The highest rates of protein synthesis in these oocytes are obtained in media containing either a divalent cation (Ca++ or Mg++) or high levels of K+. The dependence of protein synthesis on ionic environment persists through about the first 18‐24 hours of maturation (at 18°C). Normal maturation of oocytes in vitro also has specific ionic requirements for the first 24 hours. In this case, the process requires high ionic strength (T/2 = 1.0‐1.2) and divalent cations. The kinetics of K+ exchange suggest that K+ exists in the ovarian oocyte in two compartments; one in equilibrium with the exogenous medium and freely exchangeable; the other in equilibrium with the exogenous medium and freely exchangeable; the other in equilibrium with the first internal compartment and only very slowly exchangeable. The slowly exchangeable (bound) compartment contains about 95% of all endogenous K+. In hormone stimulated oocytes, the kinetics of K+ exchange are essentially the same. Oocyte adaptation to ionic environment is discussed as a possible regulatory mechanism during maturation.
Studies on the mechanism of hormonal stimulation of zinc uptake in human cell cultures: Hormone‐cell interactions and characteristics of zinc accumulation
Authors: Cox Rody P. , Ruckenstein Adriana
Published: February 2005

Adrenal steroid hormones with glucocorticoid activity increase the uptake of Zn++ in HeLa cell cultures. On the basis of the level of Zn++ accumulation induced, steroid hormones can be classified into four groups: (a) optimal inducers (e.g., hydrocortisone and prednisolone); (b) suboptimal inducers (e.g., aldosterone and corticosterone); (c) anti‐inducers (e.g., progesterone and 17 α‐methyl testosterone) which competitively inhibit induction by optimal inducers; and (d) non‐inducers (e.g., cortisone and pregnenolone) which neither induce nor inhibit the steroid‐mediated increase in Zn++ uptake. The ability of an anti‐inducer to block the effects of optimal inducers is not the result of inhibition of steroid uptake or an effect on general protein synthesis. Optimal inducers do not increase adenyl cyclase activity of HeLa cells nor can the hormone effects on Zn++ uptake be reproduced by 3'‐5' cyclic AMP. The prednisolone‐induced enhancement of Zn++ uptake is gradually lost over two or three days following removal of the hormone. Uptake of Zn++ by HeLa cells is not altered by a decrease of sodium concentration in the medium nor by changes in medium osmolarity. The uptake mechanism is not affected by subjecting intact cells to proteolytic enzymes; however, if cells are disrupted the hormone‐mediated increase in Zn++ accumulation is lost. The Zn++ taken up by HeLa cells in the presence or absence of hormone is primarily cytoplasmic in localization and appears to be distributed in a multicompartmental system.
Stimulation by epinephrine of adenyl cyclase activity, cyclic AMP formation, DNA synthesis and cell proliferation in populations of rat thymic lymphocytes
Authors: MacManus J. P. , Whitfield J. F. , Youdale T.
Published: February 2005

During the first ten minutes after the beginning of a continuous exposure of rat thymocyte populations (maintained in vitro) to epinephrine, there is an increase in the cellular concentration of cyclic AMP. The hormone also increases the activity of a crude preparation of the thymocyte's cyclic AMP‐forming enzyme, adenyl cyclase. Between 30 and 45 minutes after the beginning of exposure to epinephrine, an additional part of the cell population begins to synthesize deoxyribonucleic acid (DNA). These changes are finally followed two to four hours later by an increase of the flow of cells into mitosis.

Since cyclic AMP itself is known to stimulate both the initiation of DNA synthesis and thymocyte proliferation, and since the mitogenic action of epinephrine is shown to be potentiated by caffeine and inhibited by imidazole, it is concluded that the mitogenic action of this hormone is mediated by the cyclic nucleotide.
Early changes in the synthesis of acidic nuclear proteins in human diploid fibroblasts stimulated to synthesize DNA by changing the medium
Authors: Rovera Giovanni , Baserga Renato
Published: February 2005

When resting WI‐38 cells in a confluent monolayer were stimulated to proliferate by changing the medium, the incorporation of leucine‐3H into nuclear acidic proteins was promptly stimulated, although its incorporation into total cellular proteins was unchanged or even decreased. Three fractions, all acidic by aminoacid analysis, were extracted from the nuclei: (1) ribonucleoproteins (RNP); (2) a fraction extractable with 0.15 M NaC1; and (3) a fraction tenaciously bound to the insoluble residue (residual fraction). A first increase occurred between one and three hours after stimulation in all three fractions. The synthesis of NaCl‐soluble proteins then returned to control levels, while the synthesis of residual and RNP proteins remained high between 6 and 12 hours and increased even further at 18 hours, the peak of DNA synthesis. Pulse chase experiments indicated that the proteins synthesized in the first hour after stimulation have a turnover time of less than four hours, while the same fractions in non‐proliferating cells were stable for at least 12 hours. 2‐mercapto‐1‐(β‐4‐pyridethyl) benzimidazole, when added at the same time as the fresh medium, produced an inhibition of the increase in nuclear protein synthesis at one hour, but, if added at five hours after stimulation, it did not inhibit the increase in nuclear protein synthesis occurring at six hours. Actinomycin D (0.01 μg/ml) inhibited both the stimulation of DNA synthesis and the increases in nuclear acidic protein synthesis occurring at one and six hours after stimulation. These results seem to indicate that the serum factors responsible for the stimulation of WI‐38 cells, after binding to cells, induce an early synthesis of acidic nuclear proteins which is sensitive to very low doses of actinomycin D. In turn, the newly synthesized proteins could in some way activate in the nuclei the genes that control DNA synthesis and cell division.
Biochemistry of the bioluminescence of colonial hydroids and other coelenterates
Authors: Morin James G. , Hastings J. W.
Published: February 2005

The biochemical system responsible for the bioluminescent flashing in a number of coelenterates has been isolated and partially characterized. The system involves a molecule termed a “photoprotein,” which emits a brief (1 second) flash of light when reacted with calcium. A chelating agent such as EDTA must be used at all times to maintain the activity intact. The activity of reacted photoprotein is not restored if the calcium is removed by EDTA.
Formation of extracellular adenosine triphosphate by normal and neoplastic human cells in culture
Authors: Ågren G. , Ponten J. , Ronquist G. , Westermark B.
Published: February 2005

Normal and neoplastic human cells in culture were suspended under isotonic conditions and incubated for one minute with the substrates, including 32P‐labelled inorganic phosphate, and cofactors of the glyceraldehyde‐3‐phosphate dehydrogenase and phosphoglycerate kinase reactions (complete medium), as well as with an incomplete medium lacking ADP, NAD+ and glyceraldehyde‐3‐phosphoric acid. The neoplastic cell types incubated in the complete medium synthesized three to six times more labelled ATP than the corresponding normal cells. In the incomplete medium only insignificant amounts of labelled ATP were formed during one‐minute incubation by all types of cells. From other types of experiments it could be concluded that the labelled ATP, isolated from the cells incubated in the complete medium, was formed at the surface of the cell membranes. Only negligible amounts of enzymes engaged in the synthesis of ATP have leaked out from the cells.
Studies on the mechanism of interaction between rabbit transferrin and reticulocytes
Authors: Baker Erica , Morgan E. H.
Published: February 2005

The two stages in the uptake of transferrin by rabbit reticulo‐cytes were investigated using radioiodine‐labeled rabbit transferrin and albumin. The first stage of rapid, temperature‐insensitive uptake of transferrin was similar to albumin uptake: uptake of both proteins increased linearly with increasing protein concentration of the incubation medium up to at least 60 mg/ml, was maximal at low ionic strength and pH, and increased in the presence of basic polyamino acids. Transferrin uptake was in part dependent on the reticulocyte concentration of the blood, but albumin uptake was independent of reticulocyte concentration.

The second slower, temperature‐sensitive stage of transferrin uptake was linearly related to reticulocyte concentration, and was not found with albumin, α1‐macroglobulin or γ‐globulin. Transferrin uptake was optimal at physiological pH and ionic strength and was unaffected by basic polyamino acids. When the transferrin concentration was raised, uptake increased to reach a maximum at a concentration of 15 mg/ml.

It was concluded that the first stage of transferrin uptake was in part or wholly due to non‐specific adsorption of transferrin to erythrocytes, while the second stage of uptake was specific for transferrin and reticulocytes and depended upon normal function of the cells.
Comparative studies on the interaction of benzpyrene with cells derived from poikilothermic and homeothermic vertebrates. II. Effect of temperature on benzpyrene metabolism and cell multiplication
Authors: Fred Clark H. , Diamond Leila
Published: February 2005

The effect of incubation temperature on cell multiplication and on the efficiency of benzpyrene (BP) metabolism to water‐soluble derivatives was compared in cell cultures derived from three poikilothermic and three homeo‐thermic vertebrate species. The fish cells grew optimally at about 20°C and the amphibian and reptilian cells at about 30°C, and in general, these cells multiplied over broader ranges of temperature than the mouse, hamster or chick cells. In each cell system, the maximum temperature supporting efficient BP metabolism exceeded the maximum temperature supporting cell growth by 4 to 8°, but the range of temperatures supporting near‐maximal BP metabolism was also considerably broader in the poikilothermic than in the homeothermic vertebrate cultures.
The time of DNA replication in the cell cycle in relation to RNA synthesis in frog embryos
Authors: Remington J. A. , Flickinger R. A.
Published: February 2005

Variations in the rates of DNA and RNA synthesis during the DNA synthetic (S) period of the cell cycle have been determined in explants of early Rana pipiens embryos.

Cells of dorsal axial ectoderm‐mesoderm regions and belly endoderm regions of the embryo were partially synchronized using 5‐fluorodeoxyuridine. The partially synchronized explants were incubated continuously or at intervals during the S period with radioactive nucleic acid precursors. Autoradiographic and biochemical evidence indicates that at the gastrula, neurula and tailbud stages the DNA is replicated discontinuously in two maxima with a slowing in the synthetic rate in the middle of the S period. There is an increase in the proportion of the DNA which replicates late as development proceeds from gastrulation. At the neurula and tailbud stages the proportion of late replicating DNA is greater in the belly endoderm than in the dorsal axial ectoderm‐mesoderm.

Experiments utilizing H3‐5‐uridine indicate that RNA is synthesized discontinuously in two maxima during the S period in both dorsal axial and belly regions at the earlier neurula stage. By the tailbud stage, however, a significant decrease in the second maximum of RNA transcription occurs. RNA extraction experiments indicate that these changes can be attributed, in part, to changes in the synthesis of DNA‐like RNA. These findings are discussed in relation to cell determination.
Changes in the functional efficiency of flight muscle sarcosomes during heat death of adult Calliphora erythrocephala
Authors: Davison T. F. , Bowler K.
Published: February 2005

The temperature sensitivity of flight muscle mitochondria from adult Calliphora erythrocephala has been studied. Intact flies were treated to sublethal and lethal high temperatures, their sarcosomes were isolated and the efficiency of the coupling of oxidation and phosphorylation was measured. The temperature sensitivity of sarcosomes is correlated with the heat death point of the intact animal and the impairment of oxidative phosphorylation with α‐glycerophosphate suggests that a breakdown in ATP synthesis may be one of the causes of heat death. Restitution of enzyme activity was observed in mitochondria isolated from flies recovering from sublethal heat treatment. The results suggest that the impairment of membrane‐enzyme complexes may be important lesions in heat death.
Viral‐induced fusion of human cells. I. Quantitative studies on the fusion of human diploid fibroblasts induced by sendai virus
Authors: Velázquez Antonio , Payne Francis E. , Krooth Robert S.
Published: February 2005

Human diploid fibroblasts in monolayer cultures underwent cyto‐plasmic fusion in the presence of UV‐inactivated Sendai virus. The proportion of nuclei in the cultures which were in polykaryocytes (“polykaryocytic index”) under the conditions used in the present study, was about 0.50. When the cells were fused by the methods developed for the present study, the polykaryocytic index was substantially higher than when the conventional method was employed. The extent of fusion obtained was dependent, up to a certain degree, on the concentration of the virus and on the cell population density. The polykaryocytic index reached a maximum four to six hours after the cells were exposed to virus, but the frequency of cells with very high numbers of nuclei continued to increase for at least two days. Evidence is presented which suggests that the population of mononucleate cells is heterogeneous as regards their ability to fuse. The distribution of multinucleate cells with various numbers of nuclei roughly fits the Poisson distribution, although the frequency of cells with very large numbers of nuclei is substantially greater than the Poisson would predict.
The effect of hypertransfusion on the growth of mouse foetal liver cells transplanted into irradiated, adult recipients: Failure to detect a differential effect between cells from early and late foetuses
Authors: Tarbutt R. G. , Cole R. J.
Published: February 2005

Erythropoiesis can be reinstated in lethally irradiated mice by transplantation of adult bone marrow or liver cells from foetuses at any stage of gestation beyond the eleventh day. Hypertransfusion of the recipients abolishes erythropoiesis resulting from the transplants, even when the transplants are derived from foetuses at a very early stage of development. This suggests that erythropoietin is necessary for the successful growth of these early foetal transplants, at least in the environment of the irradiated recipient. These results are at variance with an earlier report on the susceptibility of early foetal liver transplants to suppression by hypertransfusion.
Innervation and acetylcholine sensitivity of skeletal muscle cells differentiatedin vitrofrom chick embryo
Authors: Kano Masaakira , Shimada Yutaka
Published: February 2005

Trypsin‐dissociated myoblasts from leg muscle of 12‐day chick embryos have been cultured in monolayers. After four days the muscle cultures have been confronted with fragments of the spinal cord of six‐day chick embryos.

Electrophysiological and morphological analysis demonstrate that characteristic neuromuscular transmission can develop in these cultures. Electrical stimulation of the cord fragment evokes contractions of innervated muscle fibers, from which end plate potentials and miniature end plate potentials with average frequency around one per second or more can be recorded. D‐tubocurarine (1 μg/ml) suppresses reversibly these synaptic potentials.

Non‐innervated muscle fibers are sensitive to acetylcholine over all their surface, while innervated muscle fibers are sensitive at the regions where structures suggestive of motor end plate (“bulb‐type”) are found.

We can conclude that neuromuscular connections developedin vitroin our experiments are functional in respect of transmission of impulses but also in respect of neurotrophic influences for restriction of chemosensitivity.
The rate of sedimentation of individual human red blood cells
Authors: Canham Peter B. , Jay Alfred W. L. , Tilsworth Eva
Published: February 2005

The sedimentation of individual cells was investigated in the context of the Stokes' equation for sedimenting spheres. Blood obtained from a finger prick was diluted 104 times by volume in Tris buffered Ringer solution (pH 7.4, 310 milliosmolar). A small sample of the suspension was put in a plastic, flat bottomed depression slide which was then closed with a coverslip. Thirty‐six runs were done in which a cell was kept in focus on an inverted microscope. The 250 μm descent was monitored on a two channel chart recorder. The orientation, determined by the observer as edge, oblique, or flat, and the verticle displacement, indicated by a ten turn potentiometer connected to the fine focussing knob, were recorded simultaneously. The cells studied indicated that cells are more frequently in the edge‐on orientation, that larger cells sediment faster than smaller cells despite the lower density for larger cells, and that cells wobble considerably. The biconcave cells made approximately three orientation changes per minute where one change in orientation was considered to be a rotation of 45° in any direction. Brownian motion is thought to be responsible for the wobble, or random rotations of the sedimenting cell. The edge‐to‐flat velocity ratio was 1.38 ± 0.30 S.D. which is significantly less than 1.5, the theoretical and experimental value for thin discs. There was a moderate dependence of sedimentation velocity on the square of the diameter (R = +0.5) in accordance with Stokes' Law. The variance in this relation can be accounted for by the known variation of cellular density within a normal population of red cells, and by the inherent errors of measurement.
Density dependent regulation of growth in suspension cultures of L‐929 cells
Authors: Glinos André D. , Werrlein Robert J.
Published: February 2005

Suspension cultures of L‐929 fibroblasts grown to densities of 6 to 10 × 106 cells/ml through daily centrifugation and resuspension in fresh media, have been maintained for periods up to five months without change in viability or cell size. DNA synthesis and mitosis in these cultures is limited to 5% of the cells per day, a fraction very nearly equal to the fraction of cells rendered nonviable, most likely during the manipulations associated with medium renewal. The kinetics of the flow of cells into the S and M periods following (a) renewal of the medium and (b) dilution of the high density cultures, suggest that the large majority of the cells are in a G0 or early G1 phase, resuming growth readily in response to decreased cell density. This is further indicated by the sequence of the marked shifts occurring in the cell volume distribution spectrum of the high density cultures after dilution. Long term, steady state regulation of growth with retention of intact viability was thus demonstrated in the case of a long established aneuploid cell line. The fact that this occurs in suspension but not in attached cultures, supports the concept that impairment of growth control in such cells affects predominantly regulatory mechanisms located at the cell surface rather than those concerned with intracellular synthesis and metabolism.