摘要:

AbstractHuman lymphocytes stimulated with phytohaemagglutininin vitroshow maximal14C‐thymidine incorporation when the gas phase of the cultures contains 20% O2. The rate of DNA synthesis is more affected by hyperoxic conditions than by hypoxia. Cell viability, defined by dye exclusion, is considerably less dependent on pO2than is cellular replicatio

ISSN:0021-9541    

DOI:10.1002/jcp.1040720302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe effect of external divalent cation salt solutions upon the association of an action potential and cessation of cytoplasmic streaming inNitellawas studied.Nitellacells remained excitable when immersed in solutions of CaCl2, MgCl2, BaCl2, and SrCl2. Cessation of streaming coincident with excitation occurred in solutions of CaCl2or SrCl2but not in solutions of MgCl2or BaCl2. In cells exposed to solutions containing mixtures of MgCl2and CaCl2, or MgCl2and SrCl2, it was the [Ca]/[Mg]or [Sr]/[Mg]which determined the effect of an action potential upon the rate of streaming, rather than the absolute concentrations Ca++or Sr++. The implications of these data are discussed with respect to the structure involved in the generation of cytoplasmic streaming and the relation of streaming to other types of biological motion.

ISSN:0021-9541    

DOI:10.1002/jcp.1040720303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe rate of cell division in an epithelial‐like cell line, 1S1, was examined by time‐lapse cinemicrography. When precautions were taken to insure a sufficient nutrient supply, the number of mitoses per unit time in any given area of a confluent monolayer remained constant. This “contact regulation of cell division” resulted in a steadily decreasing frequency of mitosis per cell as the culture became crowded. With the decrease was associated a gradual change in cell shape, from maximally flattened to maximally compact, due to contact inhibition of the movement of cells across one another.When cells were removed along a line scraped on a dense culture, the cells at the edge of the scrape flattened, migrated into the vacant area, and subsequently increased their frequency of mitosis to that characteristic of non‐confluent cells. Inhibition of mitosis caused by a limitation on the nutrient supply was also reversed at a line‐scrape. These observations suggest that cell flattening promoted mitosis by causing the cell membrane to expand, thereby facilitating the uptake of nutrients. The cell membrane would thus function in the mechanism of contact regulation as a transducer, for converting the pressure of the surrounding cell population into a restraining force upon the metabolism of ce

ISSN:0021-9541    

DOI:10.1002/jcp.1040720304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe pyrimidine requirements for growth ofT. pyriformisand for reversal of the growth inhibition caused by folate deprivation have been studied. The effects of thymidine and 5‐fluorodeoxyuridine have been shown to be quantitatively different from the effects of these compounds on growth and the rate of DNA synthesis in mammalian cells. Labelled nucleosides added to the medium have been found to be converted to the corresponding bases with the exception of deoxycytidine, which is first deaminated to deoxyuridine. As a result no deoxynucleosides other than thymidine specifically label DNA.The results allow deductions to be made concerning the enzymes involved in pyrimidine utilization by this organism. It is suggested that pyrimidine utilization is always channeled through uracil in the case of those compounds that can supply the pyrimidine requirement for growt

ISSN:0021-9541    

DOI:10.1002/jcp.1040720305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractVinblastine 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 G1than those in other parts of G1or 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 G

ISSN:0021-9541    

DOI:10.1002/jcp.1040720306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractCell 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

ISSN:0021-9541    

DOI:10.1002/jcp.1040720307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe rabbit lens can be maintained in culture under conditions which retain the block to proliferation characteristic of many of the cells in the normal tissuein vivo. Proliferation and cell migration subsequently can be triggered at will by the addition of serum to the medium. Serum is not required throughout the whole period of culture in order to elicit this response but only during aninitial periodwhich ends prior to the onset of both DNA synthesis and mitosis. The duration of this period of serum‐dependency is specifically related to the location (and hence the state of organization) of the cells within the epithelial layer. Some of the characteristics of the serum factors which promote these reactions and the conditions of culture which affect their activity are reporte

ISSN:0021-9541    

DOI:10.1002/jcp.1040720308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe 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 probabilityp. pcan 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 probabilityp=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.

ISSN:0021-9541    

DOI:10.1002/jcp.1040720309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractIn order to measure the total number of stem cells present in a given preparation, it is necessary to know the fraction of stem cells which settle in the spleen and form macroscopically visible colonies. The intravenous injection does not allow a direct measurement of this fraction. However, its value is established by injecting stem cells directly into the spleen, thus minimizing the dilution of stem cells through the circulation. It has been measured with this procedure, that only 4% of intravenously injected stem cells form spleen colonies.

ISSN:0021-9541    

DOI:10.1002/jcp.1040720310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractTo determine whether transcription of the genes coding for 5S ribosomal RNA depends upon the concurrent activity of the genes for 28S and 18S ribosomal RNA we studied the synthesis of 5S RNA in cultured L cells when the synthesis of the 45S precursor of 28 and 18S RNA was inhibited with low doses of actinomycin D. Synthesis of 5S RNA was measured by following the incorporation of3H uridine into components which, upon acrylamide gel electrophoresis, co‐migrated with markers of 5S RNA obtained from32P labeled ribosomes. We observed that the synthesis of 5S RNA persists in the absence of detectable 28S and 18S RNA synthesis, continuing at the normal rate for several hours and at a reduced rate for at least a generation time. This strongly supports the concept that 45S RNA is not a precursor of 5S RNA, and indicates furthermore that neither the 45S component, nor any of the intermediates involved in its transition to 28S and 18S RNA, are involved in controlling the output of the 5S genes The 5S RNA which is made during actinomycin treatment is retained predominantly in the nucleoplasm and undergoes a turnover of about 3.5% per hour. It apparently cannot be utilized when ribosome synthesis resumes following removal of the actinomyci

ISSN:0021-9541    

DOI:10.1002/jcp.1040720311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY