摘要:

AbstractErythroid colony formation in agar cultures of CBA cells was stimulated by the addition of pokeweed mitogen‐stimulated C57BL spleen conditioned medium. Both 48‐hour colonies (“48‐hour benzidine‐positive aggregates”) and day 7 large burst or unicentric erythroid colonies (“erythroid colonies”) developed, together with many neutrophil and/or macrophage colonies.In CBA mice, the cells forming erythroid colonies occurred with maximum frequency (650/105cells) in 10‐ to 11‐day‐old yolk sac and fetal liver but were present also in fetal blood, spleen and bone marrow. The frequency of these cells fell sharply with increasing age and only occasional cells (2/105cells) were present in adult marrow. A marked strain variation was noted, CBA mice having the highest levels of erythroid colony‐forming cells.The erythroid colony‐forming cells in 12‐day CBA fetal liver were radiosensitive (Do110–125 rads), mainly in cycle and were non‐adherent, light density, cells sedimenting with a peak velocity of 6–9 mm/hr. These properties are similar to those of other hemopoietic progenitor cells in fetal tissues. The relationship of these apparently erythropoietin‐independent erythroid colony‐forming cells to those forming similar colonies after stimulation by er

ISSN:0021-9541    

DOI:10.1002/jcp.1040940302

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

年代:1978

数据来源: WILEY

摘要:

AbstractChanges in membrane dynamic properties associated with membrane fusion are studied employing in vitro myoblast fusion as a model system. We utilize a microscopic fluorescence relaxation approach which makes feasible the study of local variations in membrane dynamics within surface subdomains of single intact cells. Studies of the average rotational mobility of the fluorescent probe‐1‐anilino‐naphthalene‐8‐sulfonate by this technique indicate that myoblast fusion activity is preceded by a generalized increased in membrane fluidity and that areas of cell contact between fusing cells exhibit higher fluidity and polarity, locally, than non‐fus

ISSN:0021-9541    

DOI:10.1002/jcp.1040940303

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

年代:1978

数据来源: WILEY

摘要:

AbstractIncubation of cultured B‐16 melanoma cells with 1‐methyl‐3‐isobutyl xanthine (MIX) produced a sustained rise in intracellular adenosine 3′,5′‐cyclic monophosphate (cAMP) which preceded an increase in the specific activity of tyrosinase (EC 1.10.3.1). Cultures of two clones of melanoma cells, one having a mean population doubling time twice that of the other, showed density‐dependent inhibition of growth. The tyrosinase activity of each line increased progressively during logarithmic growth, reaching maximal values shortly after the cultures achieved confluence. Intracellular cAMP levels fell during logarithmic growth, being minimal in confluent cultures. The stimulatory effects of MIX and confluence on tyrosinase activity were additive. Cells plated at high density had a lower tyrosinase activity than cells allowed to achieve a similar density by successive division from sparsely planted cultures although the intracellular cAMP levels of such cultures were not different. We support the observations of other investigators that agents which increase intracellular cAMP concentrations can both inhibit cell division and stimulate tyrosinase activity. There are, however, mechanisms for increasing tyrosinase activity and inhibiting cell division which are expressed as B‐16 melanoma cells approach confluence and which are not mediated by an increase in intracellular cA

ISSN:0021-9541    

DOI:10.1002/jcp.1040940304

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

年代:1978

数据来源: WILEY

摘要:

AbstractEarly transport changes occurring during Friend erythroleukemic cell differentiation are reported. A decrease in the rate of86Rb transport was observed beginning approximately five hours after stimulation with 1.5% dimethylsulfoxide (DMSO), a potent inducer of Friend cell differentiation. By 12 to 14 hours after DMSO addition, the transport rate had stabilized at close to 60% of control level. This decrease in the rate of86Rb transport preceded a previously reported decrease in cell volume. Other chemical inducers of Friend cells, such as hypoxanthine and ouabain, also caused early decreases in86Rb influx. In contrast, xanthine, which does not induce Friend cell differentiation, also did not affect86Rb influx.The transport of two amino acid analogues, αaminoisobutyric acid and 2‐aminobicyclo [2,2,1]‐heptane‐2‐carboxylic acid, which differ in their mode of uptake, was also measured following induction by DMSO. The transport rates of both compounds decreased after a 12‐hour exposure to DMSO. In contrast, the uptake of3H‐colchicine, a drug which diffuses passively across the cell membrane, was not significantly affected.Studies with several variant cell lines which do not synthesize hemoglobin in response to DMSO indicate that these non‐inducible cells can be divided into two classes—those that demonstrate early changes in transport very similar to the changes observed in inducible cell lines and those which exhibit only small changes in transport. Results obtained using a revertant clone have helped to distinguish between those transport changes which are associated with the induction of hemoglobin synthesis and those which are not. In addition, these early transport changes may be useful in defining the stage in the differentiation process at which a particular variant

ISSN:0021-9541    

DOI:10.1002/jcp.1040940305

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

年代:1978

数据来源: WILEY

摘要:

AbstractRibonucleotide reduction was measured in Chinese hamster ovary cells made permeable to nucleotides by treatment with the detergent Tween‐80. When compared to the respective ribonucleotide reductase activity in partially purified cell extracts, CDP and GDP reductase activities in permeabilized cells responded in a similar fashion to dithiothreitol, pH, MgCl2, FeCl3, substrate concentration and the presence of positive or negative allosteric effectors. At low protein concentrations both CDP and GDP reduction with whole cells increased linearly with cell number and was greater than the activity in corresponding cell extracts.Permeabilized cells were used to measure the level of CDP and GDP reductase in a hamster cell line resistant to the cytotoxic effects of hydroxyurea. The hydroxyurea‐resistant cell line contained four to ten times more CDP and GDP reductase activity compared to parental or revertant cell lines.The permeabilized cell assay was also used to measure CDP and GDP reductase activities in Chinese hamster ovary cells synchronized by isoleucine starvation. CDP reductase activity was low in G1 arrested cells but increased 10‐fold by 16 hours after the readdition of isoleucine to the growth medium. GDP reductase, which is present at much higher levels, is similarly induced after isoleucine addition, but only by 2‐fold. The maximum activity of both CDP and GDP reductase occurred from 14 to 16 hours after isoleucine addition, which corresponded to the period of maximum DNA sy

ISSN:0021-9541    

DOI:10.1002/jcp.1040940306

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

年代:1978

数据来源: WILEY

摘要:

AbstractDehydroascorbate, an electron affinic metabolite of vitamin C, sensitized Ehrlich ascites tumor cells, in vivo, to radiation and was selectively toxic to V79 Chinese hamster lung cells under hypoxic conditions (without radiation). The radiosensitization may involve both the electron affinic nature of dehydroascorbate as well as its ability to oxidize the intracelluar NAD(P)H and non‐protein sulfhydryl. Dehydroascorbate's oxidation of NAD(P)H required higher concentrations than other sulfhydryl oxidants such as N‐ethylmaleimide and diamide. The oxidation of NAD(P)H by dehydroascorbate could be reversed by glucose. Hypoxic cell radiosensitization of V79 cells in tissue culture by dehydroascorbate could not be easily demonstrated because of the rapid breakdown and appreciable cytotoxicity of the drug at high concentration. The cytotoxicity was found to occur with both high and low densities of V79 cells. With low cell densities small amounts of oxygen did not reduce the cytotoxicity of dehydroascorbate, but virtually eliminated the cytotoxicity of nitroaromatic electron affinic compounds (metronidazole and Ro‐07‐0582). The cytotoxicity to dense cell suspensions was found to depend upon the type of buffer included in the reaction medium. The maximum cytotoxicity was obtained in buffer free saline. The reduced form of dehydroascorbate, vitamin C, was found to be toxic only under aerobic conditions. The aerobic cytotoxicity could be prevented by the addition of catalase to the growth medium or by an increase in cell density, suggesting it was caused entirely by the production of H2O2from the oxidation of vi

ISSN:0021-9541    

DOI:10.1002/jcp.1040940307

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

年代:1978

数据来源: WILEY

摘要:

AbstractA pigmented subclone of Cloudman S91 melanoma cells, PS1‐wild type, can grow in medium lacking tyrosine. This ability is conferred by phenylalanine hydroxylase activity, and not by tryptophan hydroxylase, tyrosine hydroxylase or tyrosinase activities, although the latter activity is also present in these cells. Conversion of phenylalanine to tyrosine was measured in living cells by chromatographic identification of the metabolites of [14C]phenylalanine and in cell extracts using a sensitive assay for phenylalanine hydroxylase. Phenylalanine hydroxylase activity in melanoma cell extracts was identified by its inhibition with p‐chlorophenylalanine and not with 6‐fluorotryptophan, 3‐iodotyrosine, phenylthiourea, tyrosine or tryptophan; and by adsorption with antiserum prepared against purified rat liver phenylalanine hydroxylase, and migration of immunoprecipitable activity with authentic phenylalanine hydroxylase subunits in sodium dodecyl sulfate‐polyacrylamide gel electr

ISSN:0021-9541    

DOI:10.1002/jcp.1040940308

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

年代:1978

数据来源: WILEY

摘要:

AbstractTransformation of chicken embryo fibroblasts with Rous sarcoma virus results in cells with an enhanced rate of hexose uptake. We have examined transport of the glucose analogs 2‐deoxyglucose and 3‐0‐methylglucose in cells infected with a temperature sensitive variant of the virus. In cells shifted from restrictive to permissive conditions for transformation, increased transport of the non‐phosphorylatable analog 3‐0‐methylglucose occurs at the same time as that of 2‐deoxyglucose, a phosphorylatable analog. This enhanced rate of transport can be observed within three hours of the temperature shift. There is a corresponding decrease in the transport rate of both analogs following shift to the restrictive temperature. These results suggest that increased transport is likely to be the primary event in causing transformation‐specific changes in sugar metabolism. We have also examined uptake into the internal pools of both the phosphorylated and non‐phosphorylated forms of 2‐deoxyglucose in normal cells and in cells transformed by the wild‐type virus. These data indicate a corresponding increase in the rate of accumulation of the free sugar in transformed cells and point to transport as the rate limiting step in the accumulation of 2‐deoxyglucose in both normal and transform

ISSN:0021-9541    

DOI:10.1002/jcp.1040940309

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

年代:1978

数据来源: WILEY

摘要:

AbstractHydrocortisone has been found to induce cell spreading in rat glial C6 cells by 24 hours after its addition. This spreading phenomenon is correlated with an increase in the fraction of the peripheral cytoplasm occupied by microfilaments. Cytochalasin B causes disorganization of microfilaments in the peripheral cytoplasm of the cells. Additionally, it also prevents cell spreading in response to hormonal stimulation. High levels of calcium prevent recovery of normal microfilament organization and cell spreading following removal of cytochalasin B, but have no effect on normal microfilament organization alone. Additionally both the hydrocortisone induced spreading of C6 cells and increases in peripheral microfilaments are shown to be dependent on RNA and protein synthesis. The levels of protein co‐electrophoresing with actin are not effected by hydrocortison

ISSN:0021-9541    

DOI:10.1002/jcp.1040940310

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

年代:1978

数据来源: WILEY

摘要:

AbstractFibroblastic and epithelioid clones have been isolated from the normal rat kidney line, NRK. These clones were studied for their ability to bind epidermal growth factor (EGF), susceptibility to transformation by mouse sarcoma virus (MSV), and alteration in EGF binding upon sarcoma virus transformation. The epithelioid clones bound much more EGF than the fibroblastic clones; Scatchard plots on two of these clones, one epithelioid and one fibroblastic, showed that the higher EGF binding (1.3 × 105molecules per cell for the epithelioid clone and 1.3 × 104molecules per cell for the fibroblastic clone) was due to a greater number of receptors on the epithelioid cells rather than to a difference in the apparent affinity constant. When the clones were transformed by Moloney murine sarcoma virus the EGF binding decreased, the effect being greater with the fibroblastic clones. In 20 out of 20 independently isolated sarcoma virus transformed fibroblastic clones, the level of EGF binding was either greatly reduced or completely eliminated. In contrast to EGF, another growth factor, multiplication stimulating activity (MSA), bound to a greater extent to the fibroblastic clones than the epithelioid clones, and its binding was not decreased by sarcoma virus transformation. The results show that loss of EGF binding ability correlates with expression of the murine sarcoma virus transformatio

ISSN:0021-9541    

DOI:10.1002/jcp.1040940311

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

年代:1978

数据来源: WILEY