Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Exocytosis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1978

Effects of microfilament-active drugs, phalloidin and the cytochalasins A and B, on exocytosis in mast cells evoked by 48/80 or A23187.

Rat peritoneal mast cells were used as a model system to study the effect, on exocytosis, of three agents known to interact with microfilaments. Mast cell secretion was evaluated by fluorimetric assay of histamine and by ruthenium red staining, the latter method allowing a direct visualization and quantitation of exocytosis at the light microscopic level. Phalloidin, in concentrations up to 300 microgram/ml, was without effect on either spontaneous or 48/80-evoked secretion, even after cells were exposed to the drug for 28 h. The failure of even high doses of phalloidin to influence cellular morphology and exocytosis in the mast cell may reflect the absence of a specific membrane receptor. Cytochalasin B was likewise without effect on the response to 48/80 in normally respiring cells; but inhibited this response in the presence of Antimycin A. This inhibitory effect probably reflects the ability of cytochalasin B to block glucose transport. In normally respiring cells, neither phalloidin nor cytochalasin B affected the active expulsion of granules from exocytotic pits. Cytochalasin A, without concomitant treatment with Antimycin A, completely inhibited secretion in response to both 48/80 and A23187, and did so in low concentration. Whether this striking inhibitory effect results from an interaction with microfilaments is uncertain for the inhibition could be mimicked by nonpenetrating thiol-oxidizing agents and prevented by impermeant thiol-protecting agents suggesting that cytochalasin A may inhibit histamine release by thiol-oxidation at the cell surface. Possible surface sulfhydryls are important for membrane rearrangements accompanying exocytosis.

Animals↗
PubMed1978

Adenosinetriphosphate, calcium and temperature requirements for the final steps of exocytosis in Paramecium cells.

In Paramecium cells a synchronized discharge of trichocysts (which involves only the final exocytosis steps of membrane fusion, content discharge and membrane resealing) was achieved with ATPase-blockers, Ca2+-ionophores, lipid solvents (including lysolecithin), polyethyleneglycol, anaesthetics (Dibucain) and cationic detergents (cetyltrimethylammonium bromide (CTMAB) and cetylpyridinium chloride (CPC). Only Dibucain--and to some extent cationic detergents--can trigger exocytosis independently of extracellular Ca2+, possibly by mobilizing intracellular Ca2+. The internal free [Ca2+] necessary for exocytosis can be estimated to be greater than 10(-6) to 10(-4) M. Membrane-free trichocyst contents were isolated by density gradient centrifugation; they are converted from the contracted to the expanded state by Dibucain, CTMAB and CPC, and also by exogenous ATPase (Apyrase). Thus, it is possible to de-couple the discharge (stretching) process from membrane-related phenomena. Since only the latter are inhibited by low temperature (0 degrees C), membrane lipids probably have to be in a fluid state for exocytosis to occur. At least 2 steps appear to be involved: when membrane fusion is initiated, an independent matrix-bound system is activated for the synchronized stretching process. The energy requirement for one discharge event is estimated to be about 14 X 10(6) ATP molecules.

Adenosine Triphosphate↗
PubMed1975

X-ray microanalysis of calcium binding sites in Paramecium with special reference to exocytosis.

In Paramecium cells Ca++-stimulated triggering of the exocytosis of secretory vesicles ("trichocysts") was achieved by ionophores X-537 A or A 23187. Under triggering conditions electron dense deposits were present in some "resting" trichocysts and regularly in discharging trichocysts; upon subsequent fixation deposits occurred on the trichocyst membrane (on the inner side or within the membrane) and on the "inner lamellar sheath" from where deposits seemed to "radiate" into the secretory materials. Similar results were obtained with glutardialdehyde fixation alone which also triggers exocytosis but only at low concentrations. Element analysis by energy dispersive x-ray microanalysis ascertained the presence of Ca and P in deposits occurring in trichocysts. Those "resting" trichocysts which were devoid of deposits did not contain Ca or P enriched. Hence, an abrupt Ca++-influx into individual trichocysts just before exocytosis seems to be involved in the triggering mechanism, possible in combination with the sudden activation of an ATPase system localized at those sites of the trichocysts which primarily contain the deposits. When paramecia were treated only with Ca++ and then fixed with OsO4 plus oxalate or merely with glutardialdehyde, electron scattering deposits were formed also on the inner side of the cell membrane and within the ciliary shaft (but rarely in trichocysts). Deposits obtained on cilia (including "ciliary granule plaques") also contained Ca, P and S. Cells contain osmiophilic "calcium-storing vacuoles" which were selectively rich in Ca and S but devoid of P.

Animals↗
PubMed1977

Luminal membrane retrieved after exocytosis reaches most golgi cisternae in secretory cells.

Dextran was used to trace membrane retrieved from the luminal surface after induced exocytosis in secretory cells of rat lacrimal and parotid glands. Two different approaches were used: (a) isolated acini were incubated in vitro with dextran followed by stimulation with carbamylcholine (lacrimal) or isoproterenol (parotid) and (b) rats were injected with isoproterenol followed by dextran infusion into the parotid duct in vivo. The main findings were the same regardless of the gland source or experimental approach. Dextran was taken up initially via coated pits into smooth-surfaced apical vesicles. Shortly thereafter it was found in multiple cell compartments: within the stacked Golgi cisternae, in condensing vacuoles, and in lysosomes. Uptake was more rapid and uniform in vivo; dextran was seen in multiple cisternae of numerous Golgi complexes within 5 min after infusion. In acini incubated in vitro uptake into Golgi cisternae was more delayed and occurred with increasing frequency up to 60 min; also, more dextran was taken up into lysosomes, which were more numerous in vitro than in vivo. The results demonstrate that, after exocytosis, membrane is removed from the cell surface via vesicles that fuse with multiple cell compartments. The two novel findings are: (a) the demonstration that the tracer can reach most of the Golgi cisternae in a given stack and (b) the demonstration of the rapidity with which the process takes place (i.e., within 5 min). The findings imply that at least some membrane retrieved from the cell surface after exocytosis fuses with the stacked Golgi cisternae.

Animals↗
PubMed1979

Membrane fusion during secretion: cortical granule exocytosis in sex urchin eggs as studied by quick-freezing and freeze-fracture.

Exocytosis of cortical granules was observed in sea urchin eggs, either quick-frozen or chemically fixed after exposure to sperm. Fertilization produced a wave of exocytosis that began within 20 s and swept across the egg surface in the following 30 s. The front of this wave was marked by fusion of single granules at well-separated sites. Toward the rear of the wave, granule fusion became so abundant that the egg surface left with confluent patches of granule membrane. The resulting redundancy of the egg surface was accommodated by elaboration of characteristic branching microvilli, and by an intense burst of coated vesicle formation at approximately 2 min after insemination. Freeze-fracture replicas of eggs fixed with glutaraldehyde and soaked in glycerol before freezing displayed forms of granule membrane interaction with the plasma membrane which looked like what other investigators have considered to be intermediates in exocytosis. These were small disks of membrane contact or membrane fusion, which often occurred in multiple sites on one granule and also between adjacent granules. However, such membrane interactions were never found in eggs that were quick-frozen fixation, or in eggs fixed and frozen without exposure to glycerol. Glycerination of fixed material appeared to be the important variable; more concentrated glycerol produced a greater abundance of such "intermediates." Thus, these structures may be artifacts produced by dehydrating chemically fixed membranes, and may not be directly relevant to the mechanism by which membranes naturally fuse.

Animals↗
PubMed1978

Effects of thyrotropin on thyroglobulin exocytosis and iodination in the rat thyroid gland.

Rats, pretreated with thyroxine for 2 days, were given one or two iv injections of 500 mU of TSH; in some groups the second TSH dose was replaced by 0.75 micronmol isoproternol. The effects of the thyroid stimulators on the following parameters were studied: the number of exocytotic vesicles in the follicle cells; the incorporation of 125I into thyroid proteins, measured over periods of 5 min; and the thyroidal cAMP contents. At 2 h after TSH administration, a second dose of TSH failed to stimulate iodination while at 8 h the iodination response was "normal". Two hours after TSH the follicle cells contained practically no exocytotic vesicles but at 8 h they had a full supply of vesicles, and this was emptied by the second TSH injection. THE CAMP content was less increased by the second TSH injection than by the first one, but the stimulatory effect of the second TSH dose on cAMP was the same at 2 h and at 8 h; this indicates that the lack of iodination response at 2 h was not simply due to blocking of TSH receptors. Isoproternol, which acts on other receptors than does TSH, cause a similar cAMP increase incontrols and at 2 h and 8 h after TSH, but stimulated iodination only in controls and at 8 h after TSH; this supported the conclusion that the lack of iodination response to a second TSH dose at 2 h was not due to impairment of the adenylate cyclase-cAMP system. These observations taken together strongly indicate that a rapid iodination response to TSH depends on stimulated exocytosis which, in turn, requires a pool of exocytotic vesicles in the follicle cells. Such a coupling between exocytosis and iodination seems appropriate since by exocytosis uniodinated thyroglobulin and membrane, showing peroxidase activity histochemically, are delivered to the site of iodination, the apical cell surface.

Animals↗
PubMed1979

[Is the process of localized lysosomal exocytosis responsible for the cytolytic action of killer T-lymphocytes?].

In this paper, we formulate the hypothesis that in the process of target cell lysis a lysosomal enzyme regurgitation, performed by killer cells at the level of the target effector junction, accounts for the target lesion which precedes the lysis (lethal hit). This process of exocytosis, similar to the one described previously in polymorphonuclear neutrophils is supported by cytological studies performed directly on identified killers isolated by micromanipulation. Light and electron microscopy observations confirm a previous report which describes the effector cells rich in lysosomal bodies. In addition, when a killer cell is associated with a target cell to form a conjugate, lysosomes are concentrated near the cell junction and, after incubation at 37 degrees C, acid phosphatases may be detected at the junction. Lysosomal enzyme exocytosis explains why target lysis needs an effector target binding to occur and also the other conditions required for any exocytosis process such as Ca++ in the medium, integrity of the microtubular apparatus, a low level of cyclic AMP and energy dependancy.

Acid Phosphatase↗
PubMed1978

A freeze-fracture study of exocytosis and reflexive gap junctions in human ovarian decidual cells.

Fine-structural features of ovarian decidual cells and their mode of secretion were examined by means of freeze-fracture microscopy. Unique cortical peduncular processes contained secretory vesicles within the expanded peduncle tip, the membrane-leaflets of which exhibited a particle-poor E face adjacent to the vesicle lumen and a P face containing a greater particle number. Exocytosis from attached peduncles involved release of vesicular profiles 40-55 nm in diameter; small particles 8.5-11.5 nm in diameter were also observed at degranulation sites. In fractures revealing the E face of the plasmalemma, cytoplasmic portals at the bases of peduncular stalks were distinguishable from endocytic vesicles. The frequent occurrence of reflexive gap junctions associated with peduncles was shown by freeze-fracture. However, there appeared to be no consistent spatial relationship between gap junctions, secretory peduncles, or sites of exocytosis. Freeze-fracture analysis of the topography of reflexive gap junctional profiles revealed that such gap junctions share basic similarities with intercellular gap jum particle-free aisles. The finding in the present study of reflexive gap junctions occurring between peduncles and the cell soma, as well as between peduncles, suggests that the original definitiof the same cell should be broadened to include any gap junctional specialization formed between portions of the plasma membrane of one cell.

Cell Membrane↗
PubMed1979

Induction of exocytosis from glomus cells by incubation of the carotid body of the rat with calcium and ionophore A23187.

Carotid bodies from adult rats were electron microscopically studied after incubation in glucose-containing salt solutions containing calcium and/or ionophore A23187 or neither. In the absence of the ionophore, adding or omitting calcium had no effect on the fine structure of the glomus cells. Incubation in the medium containing both 1 mM calcium and the ionophore caused the appearance of exocytotic membrane profiles in several glomus cells. Exocytosis was not seen when only A23187 and endogenous calcium was present. For exocytosis to occur, calcium appeared to be essential and the event seemed to be due to a rise in the intracellular calcium concentration caused by the ionophore.

Animals↗
PubMed1978

Neurosecretion. XVII. Experimentally induced release of neurosecretory material by exocytosis in the insect Leucophaea maderae.

In the corpora cardiaca of the insect Leucophaea the administration of serotonin elicits ultrastructural features indicative of the extrusion of neurosecretory material by exocytosis. The response to the stimulus and the process of extrusion seem to occur at considerable speed. Nearly all of the 30 test animals, fixed at various intervals starting as early as 3 min after the injection of the drug, show granules captured at the moment of leaving the axon as well as fully exteriorized secretory material. The fact that many of these granules are much smaller than the typical neurosecretory type speaks for intracellular fragmentation of the latter prior to the discharge of this cellular product. After 25 min or more the extruded electron dense structures show signs of breakdown. 3the apparent speed of these phenomena accounts for the dearth of omega-type configurations observed in unstimulated specimens of this species. The possible relationship between the membrane phenomena involved in exocytosis and the transient protrusions of bounding membranes of neurosecretory granules described in earlier papers remains to be clarified.

Animals↗
PubMed1979

Freeze-fracture study of the chromaffin cell during exocytosis: evidence for connections between the plasma membrane and secretory granules and for movements of plasma membrane-associated particles.

Exocytosis was studied in acetylcholine-stimulated bovine adrenal medulla. During a pre-exocytotic stage, chromaffin granules are found in juxtaposition to the plasma membrane and separated from it by an electron dense space 25--27 A in width. Freeze-fracture studies show this stage to be characterized by connections between the granules and the plasma membrane. These connections are apparently cytoplasmic but bridge both membranes; they are presumably proteinaceous, but their exact nature remains to be elucidated. Later stages of exocytosis were also studied by the freeze-fracture technique; a typical feature is the lack of intramembrane particles around the fusion site. Both connections and membrane particle movement are discussed in terms of recent biochemical findings.

Acetylcholine↗
PubMed1975

The effect of puromycin and cycloheximide on vacuole formation and exocytosis in Tetrahymena pyriformis GL-9.

It has been shown that both puromycin and cycloheximide, at concentrations of 434 and 100 mug/ml respectively, produce a marked inhibition of vacuole formation and exocytosis in Tetrahymena pyriformis GL-9. These effects were analysed in a quantitative manner. At the same time as these inhibitions occurred the incorporation of 1-C14 leucine into trichloroacetic acid precipitable material was inhibited by 90% and 100% respectively over a 40 min period. This inhibition of protein synthesis by cycloheximide occurred almost immediately, whereas the inhibition of vacuole formation and egestion was delayed. The results suggested that the latter processes were dependent upon a continuing supply of proteinaceous material, of which there was only a small store within the cell. Cycloheximide inhibited exocytosis completely -nder the conditions employed (with 100% inhibition of protein synthesis) whereas puromycin (with a 90% inhibition of protein synthesis) only inhibited it by about 50%. This suggested that the amount of newly synthesized protein required for the exocytic egestion process was very small in relation to the total cell requirement for protein synthesis. The entry of both inhibitors into the cell was by means other than vacuole formation. Puromycin appeared to have some effect on vacuole formation which was unconnected with protein synthesis. Microscopic observations of living cells indicated that oral apparatus function and endocytic vacuole formation were probably both affected by the inhibitors. Chloramphenicol, at 200 mug/ml, had little effect on vacuole formation by starved cells with an exposure of an hour. The uptake of 1-C14 leucine from the growth medium was found to be a selective process, giving a concentration of about 2000 times into the cells over a 1 hr period. The results are discussed

Bacterial Proteins↗
PubMed1976

The dissociation of exocytosis and respiratory stimulation in leucocytes by ionophores.

By exploiting the unique characteristics of three ionophores, experimental conditions were found which permit the dissociation of respiratory stimulation from secretion in polymorphonuclear leucocytes. A marked stimulation of respiration was produced by ionophore X537A, which binds and transports both alkali-earth and alkali cations. The stimulatory activity of this ionophore was the same at either high or low Na+/K+ ratios in the medium and was virtually unaffected by extracellular Ca2+. A slight stimulation of oxygen consumption was also caused by the K+-selective ionophore valinomycin and by ionophore A23187, which complexes and transfers bivalent cations. Ionophore X537A and valinomycin were unable to stimulate selective release of granuleassociated beta-glucuronidase and gradually increased cell fragility, as monitored by increased leakage of lactate dehydrogenase. Ionophore A23187 slightly increased exocytosis of beta-glucuronidase. In a Mg2+-free medium, Ca2+, added simultaneously with ionophore A23187, greatly enhanced respiration and secretion of the granule enzyme. If Ca2+ was added a few minutes after the ionophore, exocytosis occurred, but no respiratory burst was observed. If the latter experiment was repeated in the presence of extracellular Mg2+, both secretion and respiration were stimulated. This effect was not produced by Mn2+ or Ba2+. It is proposed that Ca2+ is required for triggering selective secretion of granule enzymes from leucocytes is caused by an intracellular redistribution of cations, which may invovle Mg2+-dependent mechanisms.

Animals↗
PubMed1979

Synaptic vesicle exocytosis captured by quick freezing and correlated with quantal transmitter release.

We describe the design and operation of a machine that freezes biological tissues by contact with a cold metal block, which incorporates a timing circuit that stimulates frog neuromuscular junctions in the last few milliseconds before thay are frozen. We show freeze-fracture replicas of nerve terminals frozen during transmitter discharge, which display synpatic vesicles caught in the act of exocytosis. We use 4-aminopyridine (4-AP) to increase the number of transmitter quanta discharged with each nerve impulse, and show that the number of exocytotic vesicles caught by quick-freezing increases commensurately, indicating that one vesicle undergoes exocytosis for each quantum that is discharged. We perform statistical analyses on the spatial distribution of synaptic vesicle discharge sites along the "active zones" that mark the secretory regions of these nerves, and show that individual vesicles fuse with the plasma membrane independent of one another, as expected from physiological demonstrations that quanta are discharged independently. Thus, the utility of quick-freezing as a technique to capture biological processes as evanescent as synaptic transmission has been established. An appendix describes a new capacitance method to measure freezing rates, which shows that the "temporal resolution" of our quick-freezing technique is 2 ms or better.

Aminopyridines↗
PubMed1977

Calcium and stimulus-secretion coupling in the mast cell: stimulant and inhibitory effects of calcium-rich media on exocytosis.

1. Isolated rat peritoneal mast cells incubated in Ca-free media for 2 h, with or without EDTA, and observed by phase-contact microscopy, became ;bubbled' in appearance when subsequently exposed to media rich in calcium (16-110 mM).2. Electron microscopy showed the response to be ;compound' exocytosis of the sort elicited by conventional mast cell secretagogues such as antigen (in sensitized cells) and 48/80.3. The response to Ca was inhibited by withdrawing glucose and adding dinitrophenol and was thus energy-dependent.4. Mg in similarly high concentration had no such stimulant effect on Ca-deprived cells, and excess Ca stimulated only after Ca deprivation.5. It is suggested that Ca deprivation may increase the permeability of the plasma membrane of the mast cell thereby allowing some Ca, when subsequently introduced in high concentration, to penetrate and activate exocytosis; and the results are considered further support for the postulated mediator function of Ca in stimulus-secretion coupling.6. Two inhibitory effects of calcium in high concentration were detected: (a) suppression of migration or expulsion of granules from the exocytotic pits within the cellular domain; and (b) diminished sensitivity to 48/80.

Animals↗
PubMed1977

Early effects of thyroid stimulating hormone (TSH) on exocytosis and endocytosis in the thyroid.

The early effect (3 min) of thyroid stimulating hormone (TSH) on exocytosis-endocytosis in the rat thyroid follicle cell was investigated by electron microscopic morphometry. All rats used were pre-treated with thyroxine for 2 days prior to the experiments. In control rats, the membrane surface area of exocytotic vesicles, the only type of vesicle present in the apical part of the follicle cell, approximately equaled that of the apical plasma membrane. Intravenous administration of TSH caused a significant decrease in the membrane surface area of exocytotic vesicles by about 20% and a corresponding, significant increase in the membrane surface area of the apical plasma membrane by about 20%. Pseudopods were present in 4 of 6 TSH-injected rats examined, but the membrane surface area of these structures was only 15% of the increase in the surface area of the apical plasma membrane. The total membrane surface area analyzed was not influenced by injection of TSH. We conclude that the initial effect of TSH on the thyroid follicle cell is a re-distribution of membrane from exocytotic vesicles to the apical plasma membrane. This conclusion is in harmony with our previous observations which indicate that the (membrane-requiring) endocytotic response after TSH is regulated by the amount of membrane material added to the apical plasma membrane by exocytosis.

Animals↗
PubMed1977

[Demonstration of exocytosis in the sinus gland of Astacus Leptodactylus (Nordmann) under the influence of serotonin injections].

Following a serotonin injection, a rise of exocytosis in the sinus gland of the crayfish Astacus leptodactylus is observed together with an increase of the glucose level in the hemolymph. The phenomenon of exocytosis reaches a peak between 2 and 4 h after injection, wheras the highest glucose level in the hemolymph appears between 4 and 6 h after the same injection.

Animals↗
PubMed1978

Dissociation of the neutrophill functions of exocytosis and chemotaxis.

The peptide Gly-His-Gly is shown to be chemotactic for human neutrophils in vitro and for rabbit neutrophils in vivo but to be unable to induce lysosomal enzyme release from human neutrophils at sublytic concentrations. The failure of this chemotactic peptide to elicit lysosomal enzyme release provides evidence that interactions with a chemotactic receptor does not necessarily activate chemotaxis and exocytosis in the human neutrophil, thus suggesting that the presumed common pathway of exocytosis and chemotaxis may be divergent at the cell receptor and/or postreceptor level.

Albumins↗