摘要:

The isolation of synaptic vesicles rich in acetylcholine (ACh) from the electric organ of Torpedo has indeed strengthened the hypothesis of transmitter exocytosis, but soon after it was found that non‐vesicular free ACh was released and renewed upon stimulation. In contrast, vesicular ACh and the number of vesicles remained stable during physiological stimulations. In addition free ACh variations (representing the cytoplasmic pool) were correlated to the release kinetics as measured by the electroplaque discharge. Consequently, the mechanism releasing ACh from the cytoplasm in a packet form was searched at the presynaptic membrane itself. With synaptosomes isolated from the electric organ of Torpedo, it became possible to freeze them rapidly at the peak of ACh release and study their membrane and contents after cryofracture. A statistical analysis showed that the main structural change was the occurrence of large intramembrane particles at the peak of ACh release and under all release conditions. This impressive change contrasted with the stability in the number of vesicles. Another role for the vesicle was envisaged during intense stimulations when the cytoplasmic ACh and ATP pools become exhausted. The decrease in ATP leads to an increase in calcium and protons in the cytoplasm; this signals the depletion of vesicular ACh and ATP stores in the cytoplasm. Release can go on, while ATP promotes the uptake of calcium by vesicles. At the end of its cycle the vesicle will be full of calcium and will perhaps release it. As far as the mechanism of ACh release is concerned it probably depends on a membrane component (perhaps the large particles) activated by calcium and able to translocate ACh in a quantal or subquantal form. In most recent work we showed that if a lyophilized presynaptic membrane was used to make proteoliposomes filled with ACh, they released ACh upon calcium actio

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00403.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Mannose‐binding sites were detected at the ultrastructural level in nuclei of lizard granulosa cells in situ by means of mannosylated ferritin. When ultrathin sections of material embedded in glycol methacrylate were incubated with mannosylated ferritin, a strong labelling was observed over nucleoli, chromatin and the external leaflet of the nuclear envelope, but no labelling was detected in the perinuclear space except for nuclear pores. This labelling was clearly inhibited when sections were incubated in a solution containing both mannosylated ferritin and a sugar‐related neoglycoprotein (mannosylated serum albumin). These ultrastructural data supporting the existence of nuclear lectin‐like components in reptilian cells are in agreement with our previous findings about such components in nuclei isolated from mammalian cells. Owing to the unique organization of the granular component of the nucleoli in specialized granulosa cells, we are able to show that some of the mannose‐binding sites are associated with ribosomal pre

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

By blocking cells in mitosis with the anti‐fungal drug thiabendazole, it has been possible to carry out ultrastructural studies on the condensed chromosomes of the fission yeast, Schizosaccharomyces pombe. It is estimated that the DNA in these chromosomes is compacted approximately 1000‐fold, and that the nucleoprotein density is similar to that of higher eukaryotic metaphase chromosomes. A basic structural component of the condensed chromosomes appears to be a 50‐60 nm fibre, which is often visible in a loop configuration on the periphery of the chromatids. This is reminiscent of the 50‐60 nm fibre loops which are frequently seen in preparations of metaphase chromosomes, and suggests that mechanisms of nucleoprotein folding may be similar in both lower and higher euk

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The early interactions between African swine fever virus (ASFV) and monkey kidney cells in culture, and the effect of chloroquine were studied by electron microscopy. Our results indicate that ASFV uptake occurs by endocytosis: after attachment to the cell surface, the virions were seen in coated pits and were internalized by endocytosis in endosomes and finally in lysosomes. Virions in coated vesicles were never seen. All these steps were completed in about 15 min. Direct penetration of viruses through the plasma membrane was never observed. In order to elucidate the participation of an acidic intracellular compartment in the penetration of ASFV, we studied the effect of chloroquine, a lysosomotropic drug known to increase the pH of acidic intracellular vacuoles and to inhibit ASFV infection. In the presence of this drug there were no apparent alterations on binding, endocytosis and intracellular distribution of the viral particles. The main effect of chloroquine was to retain the virions in lysosomes. When the drug was removed from the medium, the viral particles disappeared and images of binding of viral membranes with the membranes of the intracellular vacuoles were obtained, suggesting that the inhibited step is the uncoating of the virus. Viral fusion with the plasma membrane was obtained when the medium was acidified to pH 5‐6. These results suggest that ASFV enters the cells by adsorptive endocytosis and that the uncoating process takes place intracellularly in a way similar to that described for Semliki Forest virus and other enveloped viruse

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The effects of the lysosomotropic weak bases, NH4Cl, methylamine and chloroquine, on the secretory process of antibody‐synthesizing cells were studied. Popliteal lymph node cells taken from rats immunized against horseradish peroxidase (HRP) were incubated with the lysosomotropic agents. The rate of secretion of anti‐HRP antibodies was measured using an indirect enzyme‐linked immunosorbent assay. These agents induced an inhibition of antibody release within 5 min, and for all four concentrations tested, maximal inhibition was reached after 15 min. A 50% inhibition was obtained with 20 mM NH4Cl, 21.7 mM methylamine and 8.8 × 10(‐4) M chloroquine. This effect was rapidly and entirely reversible, regardless of the weak base used, and it increased as the pH of the extracellular media was raised. Under these conditions, intracellular ATP contents remained normal, and protein synthesis did not undergo marked changes except with chloroquine. Inhibition of secretion was accompanied by an intracellular accumulation of antibodies which was equal to the degree of inhibition of antibody release. Immunocytochemical studies of the weak base‐treated cells performed by light and electron microscopy showed that this accumulation probably occurred within certain dilated Golgi saccules. In addition, reduced incorporation of fucose into immunoglobulins as well as partial inhibition of the secretion of fucosylated immunoglobulins were observed in the presence of weak bases. These results are consistent with the hypothesis that weak bases inhibit antibody secretion by acting within saccules of the Golgi apparatus. These saccules could maintain an acidic pH important for the migration and/or sorting of immun

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00408.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

ATP‐dependent Ca2+ transport was studied in rat parotid microsomes; the activity appears to be associated with rough endoplasmic reticulum vesicles, as indicated by marker distribution in subcellular fractions and by electron microscopic observations. Purified rough microsomes exhibit an ATP‐dependent Ca2+ accumulation and a Ca2+‐dependent ATPase activity; these activities are similarly stimulated by K+ and display an apparent Km for free calcium of 0.6‐0.7 microM. A phosphoprotein, with a molecular weight of about 110,000, was detected after short incubation with [gamma 32P] ATP and CaCl2; it is suggested that this compound represents a phosphorylated intermediate form of the Ca2+

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00409.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The high salt extract obtained from demembranated human spermatozoa contains high molecular weight proteins. These proteins are associated with an ATPase activity inhibited by sodium orthovanadate. In association with lower molecular weight proteins, they constitute a 20 S particle and are probably localized in the dynein arms (and in the radial spokes) of the human spermatozoon axonemes. Evidence is shown for a biochemical analogy between the dynein ATPases extracted from the invertebrate axonemes and the human dynein‐like ATPase described in this stud

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00410.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Young adult rats absorbed 50 p.p.m. Cd2+ added to drinking water. After 6 weeks, 3, 6 and 9 months of treatment, the ultrastructural condition of liver, kidney and muscle was observed by electron microscopy. The choice of these tissues was determined by their differences in the capacity to accumulate Cd2+: the liver is able to concentrate a considerable amount of metal, but redistributes it throughout the entire organism, while the kidney collects it in view of its elimination. Muscle contains the least Cd2+. A general regression in mitochondria cristae accompanied by a vesiculation and a fragmentation of endoplasmic reticulum appeared simultaneously in the three tissues, at as early as 6 weeks of treatment, and extended progressively with its continuation supporting evidence of a general attack of the intracellular membrane systems. Cd2+ stimulation of membrane‐degrading enzymes such as phospholipases and proteases was suggested. A concomitant diminution in glycogen stores was noted. Active synthesis of neutral lipids, especially cholesterol esters, took place in liver mitochondria of treated rats in collaboration with rough endoplasmic reticulum, and progressively generated a multiplication of electron‐transparent inclusions in cytoplasm. Isolated mitochondria from liver, kidney and muscle of Cd2+‐treated rats maintained partial energy coupling, but displayed a rapid early fall in cytochrome oxidase followed by a partial restoration after 6 months of treatment, and a progressively slackening of succinate dehydrogenase. Isolated vesicles of liver mitochondria inner membrane of treated rats behaved as intact mitochondria, indicating changes inside the membrane itself. Addition in vitro of the metal ion to mitochondria and also to inner membrane vesicles isolated from control rats revealed that Cd2+ was able to stop completely succinate dehydrogenase, but was totally ineffective on cytochrome oxidase. Membrane fixation of Cd2+ on the flavoprotein or SH associated with succinate dehydrogenase is proposed. Considering the close parallelism of the extensive depression of microsomal NADPH cytochrome c reductase and the rapid fall in mitochondrial cytochrome oxidase, it is suggested that an indirect inhibition process occurs, through Cd2+‐induced diminution of a constituent common to all cytochromes in t

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00411.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Forty‐eight and 96 hr 3H‐thymidine continuous labeling was analyzed on denervated mid‐bud limb blastemas of Pleurodeles waltlii M. In innervated blastemas, 92 to 95% of mesenchymal cells are cycling; denervation provokes an early exiting from the cycle in G0‐1(+ 15% of non‐cycling cells for a 6‐day denervation, + 20% for an 8 day denervation) and an elongation of the G1 phase. For epidermis only 25% (48 hr labeling) to 53% (96 hr labeling) of cells are cycling in innervated blastemas; denervation strongly decreases this percentage (+ 40% of non‐cycling cells for a 6‐day denervation, + 60% for an 8‐day denervation). As for mesenchyme, denervation also lengthens the G1 phase of epidermal cells. So our results contradict the conclusion of other authors claiming a G2 blockage. They account for the fall in proliferation indices and the arrest of regeneration after denervation. Finally, they show that the cell cycle of regeneration cells is controlled by the ne

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00412.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY