摘要:

AbstractIn this study the effects of retinoic acid on the binding and mitogenic activity of epidermal growth factor (EGF) in mouse fibroblast Balb/c 3T6 cells are further examined. Retinoic acid treatment of 3T6 cells results in a sixfold enhancement of125I‐labeled mouse EGF binding when assayed at 37°C. In both retinoic acid‐treated and control cells, cell‐associated125I‐EGF is rapidly internalized, degraded, and secreted. Retinoic acid treatment does not seem to have a significant effect on the rate of internalization and degradation of EGF. At 0°C, internalization of EGF is strongly inhibited in both retinoic acid‐treated and control cells. Under these conditions retinoic acid‐treated cells still exhibit a tenfold higher level of EGF binding compared to control cells. When exposed to high concentrations of EGF both retinoic acid‐treated and control cells “down‐regulate” their EGF receptors. And although the growth rate of retinoic acid‐treated cells is about half that of control cells, the rate at which EGF binding capacity is restored after down‐regulation is about three times as fast as in control cells. No direct antagonism on EGF binding was observed between the tumor promoter 12‐O‐tetradecanoyl‐phorbol‐13‐acetate (TPA) and retinoic acid. EGF is a potent mitogen for 3T6 cells in serum‐free medium; retinoic acid inhibits the mitogenic activity of EGF even though it increases EGF binding. Retinoic acid also inhibits cell proliferation induced by sa

ISSN:0021-9541    

DOI:10.1002/jcp.1041100302

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

年代:1982

数据来源: WILEY

摘要:

AbstractAction potentials evoked by depolarizing pulses were studied in immature cultured cerebral cortical neurons from chick embryos. The majority of action potentials were rather small, and they were still elicited in the presence of 10−7gm/ml tetrodotoxin (TTX), but were almost completely abolished in Na+‐free solution or by 10−5gm/ml TTX in Tyrode's solution. The elevation of external Ca2+concentration not only increased the maximum rates of rise of action potentials in normal Tyrode's solution with and without low (10−7gm/ml) TTX but also regenerated action potentials in high (10−5gm/ml) TTX‐containing Tyrode's solution or in Na+‐free solution. These high Ca2+effects were blocked by Mn2+or Co2+. These results suggest that action potentials, which were predominantly Na‐dependent, are partially contributed by Ca ions in immature chick cerebral c

ISSN:0021-9541    

DOI:10.1002/jcp.1041100303

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

年代:1982

数据来源: WILEY

摘要:

AbstractExperiments were carried out to examine the possible physiological role of disordered membrane domains in hematopoietic cell surface differentiation. The hematopoietic stem cell line 416B has been shown to bind the dye merocyanine 540 (MC540), a fluorescent probe which may be specific for disordered regions of lipid bilayers (Williamson et al., 1981). The surface receptors for the lectins Concanavalin A (Con A) and wheat germ agglutinin (WGA) exhibit patchy distributions on the surface of 416B cells which correspond to the distribution of MC540 binding regions. Appropriate incubation of these cells with either of the two lectins results in the induced formation of a cap. The binding regions for MC540 and the receptors for the other lectin become localized to the same region of the membrane by this process. Such coordinated rearrangements of surface glycoproteins associated with disordered lipid domains may play a role in the cocapping of disparate surface molecules (Raz and Bucana, 1980) or in differentiation‐related cell surface rearrangements (Schlegel et al., 1980

ISSN:0021-9541    

DOI:10.1002/jcp.1041100304

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

年代:1982

数据来源: WILEY

摘要:

AbstractProtein degradation in ten mammalian cell lines is markedly inhibited by small amounts of bovine colostrum. This response is consistent with the growth‐promoting activity of colostrum that has been reported previously. Fractionation of colostrum on DEAE cellulose showed that most of the inhibitory activity against protein breakdown in H35 cells coeluted with insulin. Insulin concentrations in different batches of bovine colostrum ranged from 0.67 nM to 5.7 nM, approximately 100‐fold higher than in blood. The sensitivity of protein breakdown in H35 or MH1C1hepatoma lines to these colostrum samples was proportional to their insulin concentrations and could largely be accounted for by the amount of insulin present. Removal of insulin from colostrum by means of a protein A‐anti‐insulin antibody affinity column was accompanied by a loss of the ability of colostrum to inhibit protein breakdown in H35 or MH1C1cells. However, in IMR90 fibroblasts, a cell line with a similar sensitivity to colostrum as the two hepatomas but very insensitive to insulin, protein breakdown was still inhibited by the insulin‐free colostrum. These results suggest that, whereas the effect of bovine colostrum in H35 or MH1C1cells is actually a response to insulin, different growth factors in colostrum account for the inhibition of protein breakdown in other c

ISSN:0021-9541    

DOI:10.1002/jcp.1041100305

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

年代:1982

数据来源: WILEY

摘要:

AbstractΔ1‐Pyrroline‐5‐carboxylic acid, an intermediate in the interconversions of proline, ornithine, and glutamate, is a potent stimulator of glucose oxidation through the hexosemonophosphate‐pentose pathway. The effect is observed in cultured human fibroblasts, Chinese hamster ovary cells (CHO‐K1), and rabbit kidney cells (LLC‐RK1). In human fibroblasts, the magnitude of the stimulation of the hexosemonophosphate‐pentose pathway is dependent on the concentration of added pyrroline‐5‐carboxylate and the effect is observed over a wide range of glucose concentrations. The mechanism of the effect is related to the generation of oxidizing potential in the form of NADP+by pyrroline‐5‐carboxylate reductase concomitant with the conversion of pyrroline‐5‐carboxylate to proline. In LLC‐RK1 cells, a cell line unique in having proline oxidase activity, proline also stimulated hexosemonophosphate‐pentose pathway activity. Although pyrroline‐5‐carboxylate markedly stimulated the hexosemonophosphate‐pentose pathway, it had no effect on glucose metabolism in the Embden‐Meyerhof pathway or the tricarboxylic acid cycle. Since the hexosemonophosphate‐pentose pathway is a source of ribose‐5‐phosphate, the precursor of phosphoribosyl pyrophosphate, the effect of pyrroline‐5‐carboxylate on the hexosemonophosphate‐pentose pathw

ISSN:0021-9541    

DOI:10.1002/jcp.1041100306

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

年代:1982

数据来源: WILEY

摘要:

AbstractHepatocytes were isolated from fasted rats by a two‐step Ca++‐free/collagenase perfusion method. The cells were subjected to centrifugation under mild conditions at 12°C in a linear metrizamide gradient (1.075–1.12 gm/cm3). The cells were distributed in the gradient a bell‐shaped manner. According to their position in the gradient the cells were divided in five different population. The heaviest population was omitted from the subsequent evaluation because it contained a high proportion of dead cells. The activity of alanine aminotransferase increased with increasing cell density indicating that the lightest cell population was enriched in perivenous cells, whereas the heaviest cell population had an excess of periportal cells. Protein synthesis was more rapid in the light (perivenous) cell population than in the heavy (periportal) cell population as measured by means of incoporation of radioactively labeled valine into protein. The distribution measured in vitro indicated approximately 80% higher rates in perivenous cells. On the other hand, the synthesis and secretion of export proteins were similar in all cell populations regardless of their density. Protein degradation measured as appearance of free valine in cell media was higher in the light (perivenous) cell population than in the other populations. Thus protein metabolism seemed to be faster in the light cell po

ISSN:0021-9541    

DOI:10.1002/jcp.1041100307

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

年代:1982

数据来源: WILEY

摘要:

AbstractRat 3Y1 cells arrested at early S by hydroxyurea traversed the remainder of S and G2 and completed mitosis after removal of the drug, irrespective of the absence of serum from the culture medium. When cells were deprived of serum for a period between early S and mitosis after removal of hydroxyurea, the cells delayed entry into S in the presence of serium in the second generation for the time length approximately equal to that of serum deprivation. When mitotic cells, which had been continously exposed to serum after removal of hydroxyurea, were deprived of serum for the next 24 hours and then were reexposed to serum, the cells delayed entry into S for more than 24 hours (more than the time length of serum deprivation). On the other hand, the cells already deprived of serum between early S and G2 in the first generation were less delayed in entry into S after postmitotic 24‐hour serum deprivation than were the cells exposed to serum between early S and G2 in the first generation. These results suggest that serum‐dependent events continue to occur in the first generation for on‐time entry into S in the next generation, and that these premitotic events (the potential for entry into S) decay if serum is absent for a long period of time after mi

ISSN:0021-9541    

DOI:10.1002/jcp.1041100308

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

年代:1982

数据来源: WILEY

摘要:

AbstractTwo recessive mutations ofParamecium tetraureliaconfer sensitivity to potassium: While wild‐type cells survive when up to 30 mM KCI is added to their growth medium, mutants cease to grow and die when levels of added KCl reach 20–25 mM. Similar sensitivities are seen to Rb+and Cs+, but not to Na+. Swimming behavior of mutants is indistinguishable from wild type when place in stimulating solutions containing Na+, K+, or Ba2+. Behavioral adaptation to low levels of K+also is indistiguishable from wild type. Flame photometry reveals that one mutant is unable to keep out K+when that ion is at high levels in the medium, while the other mutant readily leaks K+and Na+when those ions are at low levels in the medium. Both mutants have markedly lower internal Na+than does wild type. Problem with K+permeability account for the sensitivity of the one mutant to elevated external K+, but the basis of sensitivity in the other mutant is unclear. These mutants expand the range of ion regulation mutants inParameciumand demonstrate that lesions in cellular ion regulation in this organism need not result in changes in swimming behav

ISSN:0021-9541    

DOI:10.1002/jcp.1041100309

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe distribution of complement receptors CR1 and CR3 among macrophages derived from cultures of bone marrow, blood, and elicited or normal peritoneal cell population was studied. Cells and colonies from the first three sources had a common phenotype, CR1 + 3 −, whereas those from the noram peritoneal populations had either CR1 + 3 − or CR1 + 3 +. The former phenotype characterized spindle‐shaped as well as epithelial‐like macrophages; the latter was essentially restricted to colonies made up of the epithelioid cells. Both morphologic features and the CR phenotypes remained stable throughout the culture period. These phenotypic differences might be explaniend by the presence of at leas two clonally derived types of macr

ISSN:0021-9541    

DOI:10.1002/jcp.1041100310

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe possible functions of ornithine decarboxylase (ODC) and polyamines in the differetiation of mouse NB‐15 neuroblastoma cells were investigated by examining the changes of these parameters in the differentiaton and nondifferentiating NB‐15 cells over a 5‐day culture period. Differentiation of NB‐15 cells was induced by the addition of dibutyryl cyclic AMP and 3‐isobutyl‐1‐methylxanthin (IBMX) to the growth medium and was monitored by neurite outgrowth, increase of acetylcholinesterase (AChE), and RIcAMP‐binding protein. Plating of NB‐15 cells in fresh serum‐containing growth medium was accompanied by rapid growth and a marked increase of ODC activity, this early increase of ODC activity was attenuated, both in duration and in magnitude, in the differentiating cells. The spermidine content of the differentiating neuroblastoma cell was significantly lower than that of the nondifferentiating cells. In the fully differentiated neuroblastoma cells, the ODC activity and spermidine content were lower than that of the undifferentiated cells by approximately 15‐fold and five‐fold, respectively. Based on these results it is proposed that changes of polyamine metabolism may be of significance in the differentiation of mo

ISSN:0021-9541    

DOI:10.1002/jcp.1041100311

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

年代:1982

数据来源: WILEY