摘要:

AbstractIn pancreatic islets insulin secretion in response to a variety of stimulators is sensitive to the redox state of extracellular and intracellular thiols. In this connection variations of plasma glutathione (GSH) may also be of importance. In the process of stimulus‐secretion coupling, membrane thiols play an important role. One major localization of critical thiols appears to be related to the influx of calcium through the voltage‐dependent channel.Other transmembranal ion movements and the cAMP system seem to be less sensitive to thiol oxidation than calcium influx via voltage‐dependent Ca cha

ISSN:0263-6484    

DOI:10.1002/cbf.290030302

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractPhosphoinositide hydrolysis in intact pancreatic islet cells was investigated in an indirect but dynamic manner by monitoring the efflux of radioactivity from islets prelabelled with [3H]inositol. A rise in glucose concentration provoked a rapid, modest but sustained increase in effluent radioactivity, this phenomenon being abolished in the absence of extracellular Ca2+or presence of verapamil. The release of [3H]inositol was also stimulated at high extracellular K+concentration, but not by gliclazide. Whether in the presence or absence of glucose, carbamylcholine provoked a marked increase in effluent radioactivity. The response to the cholinergic agent was decreased in the presence of verapamil or absence of extracellular Ca2+and abolished in the presence of atropine or LiCl. These results suggest that an increase in cytosolic Ca activity, as caused by glucose or membrane depolarization, may cause activation of phospholipase C. In response to cholinergic agents, however, the enzymic activation, although modulated by Ca2+availability, may result directly from the occupation of muscarinic receptors.

ISSN:0263-6484    

DOI:10.1002/cbf.290030303

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractAn investigation on cell cultures obtained from temporal human bone fragments showed that they provide a suitable model for studying the mechanism involved in calcitonin action on bone cells. Furthermore they demonstrated: (1) a transitory increase in45Ca uptake that returned to control values ten minutes after the hormone was added; (2) a relation between45Ca uptake and increased cAMP concentrations when these were measured at the same time intervals; (3) a reproduction of the salmon calcitonin (sCT) effect after incubation of the cultures with either db‐cAMP or db‐cGMP and (4) inhibition of45Ca uptake and parallel decrease in cAMP levels with propanol.These results suggest that in human bone cell cultures, sCT acts as a temporary promoter of45Ca uptake, probably by activating an adenylate‐cyclase system through a β‐

ISSN:0263-6484    

DOI:10.1002/cbf.290030304

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe levels of polyamines and their synthesizing enzymes in squamous cell carcinoma of prostate implanted in intact as well as castrated male rats were determined after certain hormonal manipulations. The tumour was found to grow with an identical rate in non‐castrated and castrated rats. Polyamine content and activities of polyamine synthesizing enzymes in the tumour were found to be much lower compared to their values in ventral prostate. Moreover, the levels of these parameters were comparable in tumours whether implanted in non‐castrated or gonadectomized animals. The sequential analyses of putrescine and spermidine and activities ofL‐ornithine decarboxylase andS‐adenosyl‐L‐methionine decarboxylase of tumours at different time intervals showed a significant reduction in their levels at 30 days compared to 10 days post implantation in non‐castrated as well as castrated rats. Daily intramuscular administration of tumour‐bearing intact or castrated animals with testosterone (50 μg/g), β‐estradiol (2 μg/g) or cyproterone (12·5 μg/g) for 10 days did not influence polyamine metabolism in tumour tissue. However, either β‐estradiol and cyproterone treatments or castration were found to decrease polyamine synthesis in ventral prostate. At the same time, the testosterone replacement therapy did not allow polyamine levels or activities of polyamine synthesizing enzymes to decline in the ventral prostate of castrated rats. Our results demonstrated that contrary to ventral prostate, the polyamine metabolism in squamous cell carcinoma of prostate is independent of hormonal control. The loss of hormonal sensitivity of polyamine metabolism in the prostatic tumour could be the result of qualitative changes that occur

ISSN:0263-6484    

DOI:10.1002/cbf.290030305

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractPyruvate promotes both phosphate uptake and glucose synthesis by isolated chick kidney proximal tubule cells. 3‐Mercaptopicolinate inhibits both glucose synthesis and the promoted phosphate accumulation to the same extent. Glycerol also stimulates glucose synthesis, but does not affect phosphate accumulation. Oxygen utilization by the tissue is slightly stimulated by glycerol and pyruvate, but the enhancement of uptake by pyruvate is unlikely to result from raised cellular oxidative phosphorylation. The action of pyruvate is not a direct effect on the phosphate transporter, or on the transport of phosphate across the basolateral membrane, but entails an obligatory flux to triose phosphat

ISSN:0263-6484    

DOI:10.1002/cbf.290030306

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe properties, tissue and cellular distribution of intestinal transglutaminase have been investigated. Transglutaminase was assayed with dimethylcasein and [14C]putrescine as substrates. The enzyme has maximum activity at pH 10, although more reliable assays are made at pH 9. Transglutaminase showed an absolute requirement for Ca2+and exhibited linear assay kinetics. TheKmfor putrescine was approx. 0·15 mmol/I.Tissue distribution studies suggest transglutaminase is more active in the more muscular segments of the gut. The cellular localization in jejunum was investigated by sequential cell release techniques. Approximately 2 per cent of the total activity was found in the enterocytes and crypt cells. Most of the activity was in the submucosa and serosa suggesting an interstitial cell localization.Acute hypoplastic enteropathy induced by methotrexate was accompanied by a striking decrease in mucosal transglutaminase but the activity returned to control values by 72 h. There was no significant increase in activity during the period of intense crypt cell hyperplasia and it is concluded that intestinal transglutaminase is not implicated in crypt cell proliferation

ISSN:0263-6484    

DOI:10.1002/cbf.290030307

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractExposure of Chinese hamster ovary and African green monkey kidney cells to T‐2 mycotoxin resulted in several morphological changes which were related to inhibition of protein synthesis, the basicin vitromechanism of action of the toxin. These changes, which occurred in both cell types, included disassociation of polysomes and mitochondrial cristae alterations. In addition, CHO cells displayed membrane bleb formations similar to those found in CHO cells after exposure to established inhibitors of protein synthesis, puromycin and anisomycin. Blebs could be either a result of protein synthesis inhibition or a non‐specific early pathological response. Bleb formations were not observed in VERO cells under any experimental condit

ISSN:0263-6484    

DOI:10.1002/cbf.290030308

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe uptake and binding of59Fe,67Ga and239Pu complexed with citrate of transferrin (Tf) and of125I‐labelled Fe–Tf by human lymphoblasts (WI‐L2 cells) have been studied. Uptake kinetics of59Fe–Tf and [125I]‐Tf point to internalization by receptor mediated endocytosis.67Ga binding and uptake is always less. This may be explained by a lower affinity of Ga‐complexes for the cell surface. Factors which influence Fe uptake have a similar effect on Ga.239Pu uptake and binding, however, are different, especially in that Tf does not stimulate239Pu uptake and may actually

ISSN:0263-6484    

DOI:10.1002/cbf.290030309

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

摘要:

AbstractDigestion of pig liver chromatin with DNAse II afforded three different fractions which were characterized in terms of their DNA, RNA and tightly bound non‐histone protein content, their DNA fragment size and their template activity. Two of these fractions are soluble after digestion with DNAase II and have been separated on the basis of their different solubility in MgCl2. A third fraction is not solubilized even after extensive digestion, although the size of its DNA is comparable to that of the enzyme solubilized fractions. The three fractions show qualitatively and quantitatively different distribution of tightly bound non‐histone proteins, with specific protein components in each fraction; furthermore the non‐solubilized fraction is greatly enriched in proteins tightly bound to DNA. From all the data obtained it can be suggested that the tightly bound proteins of the insoluble fraction may play, directly or indirectly, a role in maintaining an organized chromatin stru

ISSN:0263-6484    

DOI:10.1002/cbf.290030310

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY

ISSN:0263-6484    

DOI:10.1002/cbf.290030301

出版商:John Wiley&Sons, Ltd.    

年代:1985

数据来源: WILEY