摘要:

Abstract3T6 cells resting in medium containing 0.5% serum were stimulated to prepare for multiplication by the addition of medium containing 10% serum. After a number of hours, when the rate of preribosomal RNA synthesis, total RNA content (mainly ribosomal), and the cytoplasmic content of poly A (a measure of poly A ( + ) mRNA) were considerably elevated, the serum‐rich medium was withdrawn, and the original medium replaced. The rate of preribosomal RNA synthesis began to drop within 30 minutes, but required a much longer time to fall to a new resting level. When the serum‐rich medium was withdrawn after 12 hours of stimulation, the total RNA content required 12–18 hours to fall to the resting level, whereas cytoplasmic poly A content and the rate of protein synthesis declined more rapidly, reaching a new resting level within eight hours. During the 12 hours following withdrawal of the serum‐rich medium an appreciable fraction of the cells initiated DNA synthesis. Presumably, the cellular preparations for DNA synthesis cannot be immediately reversed because of the inertial factors related to the protein‐synthesizing

ISSN:0021-9541    

DOI:10.1002/jcp.1040860402

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

年代:1975

数据来源: WILEY

摘要:

AbstractGrowth medium was conditioned by incubation on mouse embryo cells in vitro. Supplementation of agar suspension cultures with conditioned medium from primary cells, but not from established lines, readily enhanced colony development by mouse tumor cells. Only cells with the properties of myoblasts responded to conditioned medium. Other fibroblastoid cells and virus‐transformed cell lines were not affected. Myogenic cells in agar cultures grew in the presence of conditioned medium but did not differentiate. Soluble collagen at 400 m̈g/ml possessed little colony‐stimulating activity by comparison with fresh conditioned me

ISSN:0021-9541    

DOI:10.1002/jcp.1040860403

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe exposure of rat and human lymphoid cells to mitogenic concentrations of phytohemagglutinin resulted in an apparent decrease in cellular K+without a significant change in cellular Na+when the cells were washed with isotonic Hepes buffered choline chloride prior to cation determination. The apparent reduction in total cellular Na+plus K+concentration, however, was not accompanied by a change in cell volume. We inferred that the constant cell volume could occur only if the lost intracellular K+was exchanged for an external cation during the washing procedure used to prepare cells for Na+and K+measurement. This inference was supported by the quantitative recovery of lost cellular K+in the choline chloride washing solution and the demonstration that a comparable proportion of86Rb+(K+analogue)42K+was lost from prelabelled cells during choline chloride washing. Use of medium 199 with Hanks salts, 150 mM NaCl, or 100 mM MgCl2as the washing solution did not prevent K+exchange although exchange was less in the presence of MgCl2. These findings indicate that phytohemagglutinin produces a rapid alteration in lymphocyte plasma membranes so as to allow abnormal K+exchange. This observation is of importance because investigators who measure intracellular solutes in phytohemagglutinin‐treated lymphocytes must consider the possibility of loss during preparative washes. Also, changes in membrane permeability following phytohemagglutinin treatment may modulate mitogenesis and/or permit the transmission of chemical messages between cell

ISSN:0021-9541    

DOI:10.1002/jcp.1040860404

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

年代:1975

数据来源: WILEY

摘要:

AbstractCellular feeder layers, prepared from normal blood leukocytes, usually stimulate human marrow to form colonies. A significant increase in the stimulating activity of unseparated leukocyte feeder layers is brought about following the removal of dense leukocytes in a manner which avoids enrichment of any remaining cell type. Restoration of dense leukocytes to a dense leukocyte depleted leukocyte feeder layer results in the reduction of stimulating activity to that of an unseparated leukocyte feeder; however, addition of dense leukocytes to unseparated leukocyte feeder layers has no effect on the stimulatory activity, over the range of concentrations used in this study.

ISSN:0021-9541    

DOI:10.1002/jcp.1040860405

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe synthesis and degradation of pectoralis myosin have been investigated in chickens 15–23 days after hatching. An essentially nonreutilizable tracer amino acid was used to demonstrate differences in the rates of synthesis and degradation of myosin isolated from normal and hypertrophied, dystrophic breast tissue. The analyses have shown that the dystrophic system synthesizes myosin faster than the normal system and that only myosin in dystrophic pectoralis is degraded during the experimental period. Double label experiments have indicated that the heavy chains of dystrophic myosin are destroyed at a rate greater than that characteristic of the light chain

ISSN:0021-9541    

DOI:10.1002/jcp.1040860406

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe present studies astablish the cellular pool of aspartate as the major source of this amino acid used during the biosynthesis of skeletal muscle myosin. This precursor‐product relationship has been established in growing, normal pectoralis and has been suggested in hypertrophied, dystrophic pectoralis. Specific activities of aspartic acid in plasma and cellular pools corrected for extracellular space contributions have been correlated with aspartate incorporation into myosin. These data have been coupled with quantitative data on myosin accumulation and have established the cellular pool as the major precursor pool. The data also give further insight into some of the factors responsible for the observation that in vivo dystrophic tissue gives higher levels of aspartate incorporation than normal tissu

ISSN:0021-9541    

DOI:10.1002/jcp.1040860407

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

年代:1975

数据来源: WILEY

摘要:

AbstractActively growing HeLa monolayer cultures briefly exposed to the culture fluids (CF) from confluent HeLa cultures and labeled simultaneously or subsequently, incorporated less3H‐uridine (3H‐UR) but more3H‐adenosine (3H‐AR) than control cultures similarly exposed to fresh medium and labeled. Exposure to CF inhibited the uptake as well as the incorporation of3H‐UR by cultures. The inhibition of3H‐UR incorporation by CF‐exposed cultures could be reduced by increasing the concentration of3H‐UR in the labeling medium. Both the inhibition of3H‐UR incorporation and the stimulation of3H‐AR incorporation were prevented by washing the CF‐treated cultures with phosphate buffered saline before labeling. Similarly, both effects could be producted in HeLa cultures exposed to fresh medium containing 1 × 10−5M uridine instead of to CF. Therefore, the observed effects of CF on label incorporation were probably due to the presence of uridine or a related compound, and the inhibition of3H‐UR incorporation resulted from reduced uptake of3H‐UR rather than from reduced RNA synthesis by exposed cells. The active agent in the CF, formed only when cultures were incubated at physiological temperatures, was not a product of medium decay. It was a cellular product formed equally well by cultures incubated in medium contai

ISSN:0021-9541    

DOI:10.1002/jcp.1040860408

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

年代:1975

数据来源: WILEY

摘要:

AbstractAfter the re‐addition of serum in the presence of adenosine (25 m̈M), the entry of quiescent, serum starved BHK 21 cells into DNA synthesis follows first order kinetics after a well defined lag period of eight hours, and with a rate constant dependent on serum concentration. Initiation of DNA synthesis under these conditions can therefore be considered to be a random event occurring with a “Transition Probability” determined by the serum concentration. In the presence of adenosine, the change of Transition Probability following the addition of serum occurs abruptly. In the absence of exogenous adenosine, however, the change of Transition Probability after serum addition appears to be both gradual and bi‐phasic. The initial changes in the absence of adenosine, though smaller in magnitude, display a similar dependence on serum concentration to the changes occurring in the presence of the nucleoside. In contrast, the secondary gradual increase of Transition Probability in the absence of added purines exhibits a higher serum requirement. It is suggested that the regulation of Transition Probability by serum involves some purine‐dependent process, and that in the absence of an exogenous supply this becomes limited by endogenous synthesis which in turn may be dependent on serum con

ISSN:0021-9541    

DOI:10.1002/jcp.1040860409

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

年代:1975

数据来源: WILEY

摘要:

AbstractThere is a low uptake of leucine in suspension cultures of 3T3 cells relative to the uptake in sparse monolayer cultures. The pattern of uptake of deoxyglucose is similar in suspension and monolayer cultures and changing the medium or adding serum stimulates uptake under both culture conditions. The uptake of uridine and adenosine is greater in suspension culture than in monolayer culture. Cells do not multiply in suspension culture but do multiply in monolayer culture and thus there is a correlation between uptake of leucine and conditions which stimulate cell multiplication, but no correlation of the uptake of deoxyglucose, uridine and adenosine with these conditions.

ISSN:0021-9541    

DOI:10.1002/jcp.1040860410

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

年代:1975

数据来源: WILEY

摘要:

AbstractSpontaneous variants of the IgA immunoglobulin secreting mouse myeloma, S194–2, were isolated by cloning the line on soft agar and screening for the loss of secreted S194 immunoglobulin. Because S194 IgA possesses DNP binding activity, the screening method was designed to test for clonal secretion of antibody which specifically precipitated DNP‐ferritin conjugates. Precipitates formed over IgA secreting S194 clones, whereas none were evident over nonsecreting XCl clones nor IgG secreting MOPC 21 clones (MOPC 21 IgG does not bind DNP). In addition the method was sensitive to the amount of immunoglobulin secreted. By continual selection of exceptionally reactive clones with this assay, a S194 culture was obtained which secreted five to six times as much IgA as the original mass culture. Spontaneous variants were isolated from six independent subclones of this parent line with an overall frequency estimated at 2.7 × 10−5per cell per generation. Biochemical analysis of these variants showed that all of them secreted reduced or undetectable amounts of IgA. No variants were obtained which secreted IgA molecules altered at the DNP binding site, or which secreted immunoglobulin subunits alone. Variants of the latter class have, however, been obtained in high frequency in other myeloma strains by other investi

ISSN:0021-9541    

DOI:10.1002/jcp.1040860411

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

年代:1975

数据来源: WILEY