摘要:

AbstractAn analysis of water vapor sorption by cysts of the brine shrimp,Artemia salina, has shown that at environmental water activities (aw) of 0.95 or less, the cysts equilibrate with the awof their environment. Above this awthe metabolic activity of the cysts participates directly in their water content, and equilibration does not occur. In contrast, dried cysts killed by heat treatment or exposure to ammonia fumes equilibrated with all values of awexamined. Analysis of the temperature dependence of sorption isotherms revealed that below cyst hydrations of about 0.3 g H2O/g dried weight the temperature coefficient for water sorption was negative, but became positive at hydrations appreciably in excess of this value. Estimates for the differential and integral net enthalpy and entropy changes accompanying the sorption of water have been calculated from isotherms. These results have been interpreted and integrated with those from previous work on the hydration‐dependence of metabolic activity. All of the examined hydration properties of the cysts have been shown to be due chiefly to the cellular component, and not the acellular shell. Analysis of the data by the Bradley equation has shown that the hydration behavior of the shell obeys this relationship, whereas that of the cellular component does no

ISSN:0021-9541    

DOI:10.1002/jcp.1040940202

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe tyrosinase (EC 1.14.18.1) activity of cultured mouse melanoma cells B16 in the stationary phase of growth, depends greatly on the pH of the medium and the kind of sugar present.The enzyme activity of a homogenate of cells grown at pH 7.2 in Eagles's MEM supplemented with 10% new born calf serum and containing galactose in place of glucose, was about ten times that of a homogenate of cells cultured at pH 6.3 in the same medium. The tyrosinase activity changed reversibily on changing the pH of the culture medium.When cultured at a constant pH of 7.2, cells grown with 1 mM galactose had about five times higher tyrosinase activity than cells grown with 1 mM glucose. Only a small amount of lactate accumulated in cultures with glucose and it had little effect on the enzyme activity.These two findings explain the very low tyrosinase activity of cells cultured in medium with 5 mM glucose: the low activity is due to the presence of glucose and to the low pH resulting from conversion of glucose to lactic acid.

ISSN:0021-9541    

DOI:10.1002/jcp.1040940203

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe over‐all rates of protein synthesis, degradation and net accumulation were estimated in rapidly growing young and slowly doubling old cultures of chick fibroblasts. We find that not only the rate of protein synthesis is reduced in senescent cultures, but the average rate of protein degradation is also slowed down considerably. This decrease in the rate of protein breakdown in aging cells stands in contrast with the previously observed acceleration of this process by other conditions (such as serum deprivation or overcrowding) that lead to the cessation of cellular growth. Though the retarded protein degradation may contribute to the accumulation of abnormal proteins in senescen cells, we find that the breakdown of grossly abnormal puromycin peptides proceeds equally rapidly in young and old cultures.The protein content of senescent cells increase by 1.8‐fold as compared to young cells, while the average cell volume is increased even more (almost 5‐fold). By contrast, consideration of the over‐all balance of protein metabolism in these cells indicaes that the average concentration of metabolically turning‐over proteins is somewhat higher in senescent than in young fi

ISSN:0021-9541    

DOI:10.1002/jcp.1040940204

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

年代:1978

数据来源: WILEY

摘要:

AbstractFollowing growth stimulation of rat embryo fibroblast (REF) cells previously arrested in G1by serum deprivation, there occurs a large increase in the synthesis of the polyamines putrescine, spermidine and spermine. Methylglyoxal bis(guanylhydrazone) (MGBG), a potent inhibitor of S‐adenosylmethionine decarboxylase can block the accumulation of both spermidine and spermine over a period of several days. Under such conditions REF cells treated with MGBG will approximately double in number and then become growth‐arrested again predominantly in the G1phase of the cell cycle. REF cells therefore appear to contain sufficient spermidine and spermine to progress through one cell cycle before the intracellular levels of these polyamines is reduced sufficiently to arrest growth in the absence of continued polyamine synthesis. Limitation of intracellular polyamine levels is therefore not the mechanism by which deprivation of serum growth factors arrests cell growth. While continued growth is nevertheless dependent on polyamine synthesis, this cell type is capable of limited proliferation in its absence. Addition of spermidine or spermine to MGBG‐arrested REF cells results in a rapid resumption of proliferation demonstrating that either polyamine can fulfill the role played by these polyamines in the growth process. Low levels of spermidine and spermine therefore arrest this cell type at a resriction point in G1at which it is decided whether the intracellular level of these polyamines is sufficiently high to enable a cell to enter into and complete a new cell cycle. This polyamine‐sensitive restriction point is considered to be analogous to the restriction point(s) in G1at which serum and nutrient limitat

ISSN:0021-9541    

DOI:10.1002/jcp.1040940205

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

年代:1978

数据来源: WILEY

摘要:

AbstractCells from thigh muscles of fetal rats proliferate readily in vitro in medium containing homologous adult rat “plasma.” As the donor animals mature, these cells become unable to make DNA and proliferate in “plasma” medium, but retain an ability to proliferate in medium containinig fetal bovine serum (FBS). This age‐related loss of the ability to proliferate in “plasma”‐medium is due to an increasing need by the cells for an exogenous prereplicative promoter which is found in FBS and a crude preparation of bovine luteinizing hormone. Adult cells (and possibly fetal cells) also require a “cycle‐completion” factor which is found in FBS and adult rat “plasma.” The requirements for such external proliferative promoters is completely eliminated by neoplastic transformation in vivo, and neoplastic adult cells isolated from a nickel sulfide‐induced mixed rhabdomyo‐fibro‐sarcoma can make DNA and proliferate in vitro in the complete abse

ISSN:0021-9541    

DOI:10.1002/jcp.1040940206

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

年代:1978

数据来源: WILEY

摘要:

AbstractThere are clones of myeloid leukemic cells that can be induced to differentiate by the normal differentiation‐inducing protein MGI to form Fc and C3 rosettes, mature macrophages and granulocytes. One of these clones (MGI+DMSO+) was also inducible by dimethylsulfoxide (DMSO) for C3 but not Fc rosettes, and for mature macrophages but not for mature granulocytes. Other clones (MGI+DMSO−) were inducible by MGI but not DMSO and a third type of clone (MGI−DMSO−) was not inducible by either compound. Clones that differed in their inducibility by DMSO showed a similar inhibition of cell multiplication by DMSO. The results indicate, that some stages of differentiation can be induced by DMSO in an appropriate clone of myeloid leukemic cells and that there are different cellular sites for induction by DMSO

ISSN:0021-9541    

DOI:10.1002/jcp.1040940207

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe effects of an acridine half‐mustard, ICR 191, on the growth rate and ploidy of four haploid and two diploid lines ofRana pipienscells in culture were studied. Growth curves indicate that the haploid and diploid cell lines were equally resistant to a 4‐hour exposure of this drug (0.1 μM to 10 μM). ICR 191 treatment induced the haploid cell cultures to become diploid. The proportion of diploid cells increased progressively with respect to time after the 4‐hour exposure period. The greater the concentration of ICR 191 applied, the more rapid the rate of conversion. Autoradiographic determinations of percent labelled nuclei indicate that DNA synthesis was not inhibited in haploid or in diploid cells. Therefore, the increased proportion of diploid cells did not originate from the small percentage of diploid cells in the initial population. Instead, the haploid cells were converted to diploid cells. Time lapse cinematography indicated that the conversion mechanism was other than cell fusion. Conversion to higher ploidy did not occur when diploid cell cultures were exposed to

ISSN:0021-9541    

DOI:10.1002/jcp.1040940208

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

年代:1978

数据来源: WILEY

摘要:

AbstractBy repeated selection for longer survival in an isotonic solution of glycerol, a stable subline of Novikoff rat hepatoma cells has been isolated. The cells exhibit markedly increased resistances to osmotic lysis in isotonic solutions of glycerl. They are twice as large and have twice as many chromosomes as cells of the parental line. It is suggested that the osmotic stress procedure can be extended for the selection of numerous kinds of mutants and can be used as a method of analysis of membrane properties.

ISSN:0021-9541    

DOI:10.1002/jcp.1040940209

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

年代:1978

数据来源: WILEY

摘要:

AbstractProlactin and growth hormone production were measured in a rat pituitary tumour cell strain (GH3) after treatment with cortisol (5 × 10−6M), thyroliberin (2.5 × 10−6M) and 17β‐estradiol (10−6M). The changes in hormone production were related to alterations in cell growth rate and cell cycle distribution. Cortisol inhibited prolactin production, stimulated growth hormone production and reduced the cellular growth rate measured two days after start of treatment (maximum about 40% inhibition). Flow‐micro fluorometric analysis of DNA distributions showed that cortisol treatment reduced the relative number of cells in S phase (maximum effect about 50%) with a compensatory increase of the proportion of cells in G1phase. The lack of inhibition of prolactin production after three days of cortisol treatment may partly be related to the increased number of cells in G1phase. Thyroliberin and 17β‐estradiol did not significantly affect cell growth after six days of treatment, although the fraction of cells in S phase was reduced by approximately 40% with a corresponding increase of cells in G1phase. For thyroliberin and 17β‐estradiol, the stimulatory effect on prolactin production and the inhibitory effect on growth hormone production witin a period of treatment of six days cannot be explained by a shift in cell cycle distributions. None of the three hormones influenced the growth fraction which was equal to unity.In conclusion, thyroliberin and 17β‐etradiol are able to change prolactin and growth hormone production without altering the cell cycle distribution. However, the effects of cortisol on prolactin and growth hormone production may partly be due to an alteration in cell cycle traverse resulting in an increased number of

ISSN:0021-9541    

DOI:10.1002/jcp.1040940210

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

年代:1978

数据来源: WILEY

摘要:

AbstractThree red cell populations have been distinguished in genotypically low potassium (LK) newborn sheep by an improved electrical sizing method and were best approximated by a logarithmic normal distribution. Labeling studies with51Cr and59Fe exclude transformation of the three red cell populations into each other. Population I, consisting of large red cells (mean volume 36 μm3), with a comparatively slow electrophoretic mobility is present at birth and disappears within three to four weeks from circulation. These cells possess a high potassium (HK) steady state concentration, a K+pump influx activity at least 5‐fold greater than observed in adult LK red cells, very low amounts of the L antigens generally associated with the LK property, and do not respond to the stimulatory action of the L antibody. The first population is gradually replaced by population II comprising small red cells (mean volume 28 μm3) of intermediate electrophoretic mobility and with a peak production around day 20 after birth. The potassium concentration, [K+]c, in these cells appears to be lower than in the cells of population I but the L antigen content is increased. Formation of population III (mean volume 30 μm3and comparatively fast electrophoretic mobility) follows closely that of population II and is preceded by a sharp increase in reticulocytosis. The red cells of population III exhibit parameters characteristic for adult LK cells: low [K+]cand K+pump activity, fully developed L antigen content, and an almost maximal response to the K+pump stimulating effect of anti‐L. In L and M antigen positive LK red cells of newborn sheep, the development of the M antigen parallels that of the L antigen. The data are consistent with the hypothesis that cellular replacement and not maturation is the major factor in controlling the HK‐LK transition in newbo

ISSN:0021-9541    

DOI:10.1002/jcp.1040940211

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

年代:1978

数据来源: WILEY