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H Plattner

Publications and source records attributed to H Plattner.

At least 91 records · Page 5Linked to original sources
PubMed1987

Ultrastructural analysis of dynamic cellular processes: a survey of current problems, pitfalls and perspectives.

Dynamic phenomena in cells that can be analyzed on the ultrastructural level comprise so different aspects as ion shifts, conformational changes of macromolecules, membrane particle rearrangements, lipid phase transitions, protein-protein interactions (notably ligand-receptor interactions, including their sorting and sequestration), reversible membrane-to-membrane contacts, membrane fusions, transcellular transport phenomena, restructuring of cytoskeletal elements, ciliary and flagellar beat, cell shape changes, etc. Only some of these phenomena can be analyzed under stationary conditions, while others are unidirectional and sometimes very rapid. Therefore, the methodical approaches to be used (primary methods and follow-up procedures) might be widely different. Quite different methods are available, such as fast freezing, specific labeling, low temperature processing and/or analysis, x-ray-microanalysis, etc. Only occasionally are there alternative non-ultrastructural control methods available. This survey paper tries to analyze the degree of reliability (or uncertainty) of current methods and to pinpoint the goals and eventually also new methodical perspectives for an integrative approach to analyze dynamic cellular processes with the high temporal and spatial resolution provided by the electron microscope.

Animals↗
PubMed1986

Ultrastructural and cytochemical characterization of adrenal medullary plasma membrane vesicles and their interaction with chromaffin granules.

Plasma membrane vesicles obtained by density gradient centrifugation of bovine adrenal medullary homogenates were analyzed by electron microscopic methods, including negative staining, ultrathin sections and freeze-fracture replicas. Rapid freezing showed the intramembrane structure of plasma membrane vesicles to be distinct from that of other organelle membranes, such as chromaffin granules. Cytochemical demonstration of acetylcholinesterase (EC 3.1.1.7) activity on most membrane profiles confirmed that plasma membrane vesicles are derived predominantly from plasma membranes. About half of the plasma membrane vesicles were smaller than 0.15 micron and almost none larger than 0.55 micron. Practically all were composed of single shells. Most vesicles were impermeable to cytochemical markers of the size of Ruthenium red (Mr 800) and none were permeable to markers larger than 40 kDa. Surface charge probes, concanavalin A binding and endogenous actin decoration with heavy meromyosin indicated that the major fraction of plasma membrane vesicles is oriented right-side-out. A minor population with opposite orientation could also be detected. Isotonic ionic media caused vesicle aggregation in suspensions of plasma membrane vesicles and chromaffin granules. Freeze-fracturing always revealed clusters of membrane-intercalated particles at the sites of contact between aggregated membranes.

Adrenal Medulla↗
PubMed1986

Lectin binding sites in Paramecium tetraurelia cells. I. Labeling analysis predominantly of secretory components.

Though all three lectins tested (ConA, RCA II, WGA) bound to the entire cell membrane, none bound selectively to the docking site of secretory organelles (trichocysts); the same results were achieved with FITC-conjugates, or, on the EM level, with peroxidase- or gold-labeling. Only WGA triggered the release of trichocysts and none of the lectins tested inhibited AED-induced synchronous exocytosis. When exocytosis was triggered synchronously in the presence of any of these three lectins (FITC-conjugates), the resulting ghosts trapped the FITC-lectins and the cell surface was immediately afterwards studded with regularly spaced dots (corresponding to the ghosts located on the regularly spaced exocytosis sites). These disappeared within about 10 min from the cell surface (thus reflecting ghost internalization with a half life of 3 min) and fluorescent label was then found in approximately 6-10 vacuoles, which are several microns in diameter, stain for acid phosphatase and, on the EM level, contain numerous membrane fragments (otherwise not found in this form in digesting vacuoles). We conclude that synchronous massive exocytosis involves lysosomal breakdown rather than reutilization of internalized trichocyst membranes and that these contain lectin binding sites (given the fact free fluorescent probes did not efficiently stain ghosts). Trichocyst contents were analyzed for their lectin binding capacity in situ and on polyacrylamide gels. RCA II yielded intense staining (particularly of "tips"), while ConA (fluorescence concentrated over "bodies") and WGA yielded less staining of trichocyst contents on the light and electron microscopic level. Only ConA- and WGA-staining was inhibitable by an excess of specific sugars, while RCA II binding was not. ConA binding was also confirmed on polyacrylamide gels which also allowed us to assess the rather low degree of glycosylation (approximately 1% by comparison with known glycoprotein standards) of the main trichocyst proteins contained in their expandable "matrix". Since RCA II binding could be due to its own glycosylation residues we looked for an endogenous lectin. The conjecture was substantiated by the binding of FITC-lactose-albumin (inhibitable by a mixture of glucose-galactose). This preliminary new finding may be important for the elucidation of trichocyst function.

Animals↗
PubMed1986

Lectin binding sites in Paramecium tetraurelia cells. II. Labeling analysis predominantly of non-secretory components.

All the lectin-FITC conjugates tested (ConA, RCA II, WGA) bind to the surface of Paramecium cells. Yet only WGA yields a distinct fluorescent pattern; it contours the basis of cilia and in some cells it brilliantly stains a few neighbouring rows of the regular surface fields in the anterioventral region (a region known to contain extensive fields of linear aggregates of freeze-fracture particles and to be engaged in conjugation). Incubation in vivo with WGA-FITC resulted in the selective labeling of the cytopharyngeal region as well as of the cytoproct. On Lowicryl K4M sections, WGA-gold probes concomitantly labeled disk-shaped vesicles that are assumed in the literature to serve as shuttle vesicles between these two cell regions and, thus, to connect forming and defecating digesting vacuoles (stages DV I and DV IV). On K4M sections WGA-Au stains also most other components of the lysosomal system. Also on K4M sections RCA II-Au labeled the walls of bacteria contained in DV I and II type digesting vacuoles (but not lysosomes identified bona fide by their size and shape and by their frequent vicinity to or continuity with digesting vacuoles). The WGA data largely support previous conclusions on the possible functional connection of all these elements (DV I-IV, smaller lysosomes, disk-shaped vesicles etc.) of the lysosomal system in Paramecium, as proposed by Allen and his group on the basis of other lines of evidence. As shown in the accompanying paper, ConA-FITC stained ghosts (formed after massive trichocyst exocytosis) also abut into DV-like structures. The different results obtained with the three lectins tested reflect the complex sorting machinery contained in the elaborate lysosomal system of a Paramecium cell. In the cytosol, finally, there occurs a particularly intense staining with ConA-gold, applied to Lowicryl sections, that probably represents glycogen-like particles. The same procedure reveals some weak staining of secretory contents and of nuclear structures.

Animals↗
PubMed1986

ATP keeps exocytosis sites in a primed state but is not required for membrane fusion: an analysis with Paramecium cells in vivo and in vitro.

We have tried to specify a widespread hypothesis on the requirement of ATP for exocytosis (membrane fusion). With Paramecium tetraurelia cells, synchronously (approximately 1 s) exocytosing trichocysts, ATP pools have been measured in different strains, including wild type cells, "non-discharge" (nd), "trichless" (tl), and other mutations. The occurrence of a considerable and rapid ATP consumption also in nd and tl mutations as well as its time course (with a maximum 3-5 s after exocytosis) in exocytosis-competent strains does not match the actual extent of exocytosis performance. However, from in vivo as well as from in vitro experiments, we came to the conclusion that ATP might be required to keep the system in a primed state and its removal might facilitate membrane fusion. (For the study of exocytosis in vitro we have developed a new system, consisting of isolated cortices). In vivo as well as in vitro exocytosis is inhibited by increased levels of ATP or by a nonhydrolyzable ATP analogue. In vitro exocytosis is facilitated in ATP-free media. In vivo-microinjected ATP retards exocytosis in response to chemical triggers, whereas microinjected apyrase triggers exocytosis without exogenous trigger. Experiments with this system also largely exclude any overlaps with other processes that normally accompany exocytosis. Our data also explain why it was frequently assumed that ATP would be required for exocytosis. We conclude that membrane fusion during exocytosis does not require the presence of ATP; the occurrence of membrane fusion might involve the elimination of ATP from primed fusogenic sites; most of the ATP consumption measured in the course of exocytosis may be due to other effects, probably to recovery phenomena.

Adenosine Triphosphate↗
PubMed1986

Calmodulin in Paramecium tetraurelia: localization from the in vivo to the ultrastructural level.

Monospecific polyclonal antibodies against Paramecium tetraurelia calmodulin were prepared and labeled for calmodulin localization on different levels of resolution: by microinjection into living cells; with isolated cell surface complexes (cortices); on the ultrastructural level, using Lowicryl sections of non-permeabilized cells (with colloidal gold-protein A labeling of antibodies bound); or using permeabilized and gently fixed cells for incubation with peroxidase- or microperoxidase-tagged antibodies. Sites selectively labeled above cytoplasmic background largely coincided, irrespective of the method used, although sensitivity, resolution, and liability to redistribution of antigen were quite different. (The methodological diversification applied allowed for their mutual control.) Nonspecific binding can be largely excluded, since all these methods gave negative results with pre-immune sera. We reached the following conclusions on sites with selective calmodulin binding (above cytoplasmic background level) in P. tetraurelia cells. A pool of calmodulin co-localized with F-actin, not only in the cortex (including fibrous materials around ciliary basal bodies) but also around food vacuoles (phagosomes) and, to a lesser degree, around the buccal cavity. Trichocyst docking sites on the cell membrane, and coated pits also displayed calmodulin labeling, thus indicating the potential involvement of calmodulin in exo-endocytosis processes. Calmodulin was also enriched on membranes of compartments with presumable ion (possibly Ca2+) transport capacity, such as trichocysts and the osmoregulatory system. Not selectively labeled were nuclei, mitochondria, and some small lysosomal organelles (as identified in vivo by rhodamine 123 or acridine orange fluorescence, respectively).

Actins↗
PubMed1986

Filamentous actin in Paramecium cells: mapping by phalloidin affinity labeling in vivo and in vitro.

In living Paramecium cells, microinjected rhodaminyl (R)-phalloidin rapidly labels a thin cortical layer. This can be more clearly resolved with microinjected and fixed cells (allowing for better resolution) as well as with isolated pellicles (surface membrane complexes with trichocysts, microfilaments, and mitochondria attached). Labeling of a longitudinal and perpendicular pattern, reflecting the relief of the cell surface, and labeling of ciliary basal bodies then becomes clearly visible. Other structures labeled by R-phalloidin are the surfaces of food vacuoles of different sizes and, although inconsistently, the borders of the buccal cavity. Small acidic compartments (as identified by acridine orange fluorescence vital staining), probably representing acidosomes and small lysosomes, were not labeled. F-actin on food vacuole surfaces may somehow be involved in intracellular transport or fusion processes. No labeling was observed in association with the osmoregulatory system (contractile vacuoles and their ampullae and radial canals). The specificity of in vivo labeling obtained was supported by the abolition of R-phalloidin labeling when isolated pellicles were pretreated with unlabeled phalloidin or with DNAse I. It was also possible to discriminate among different layers of R-phalloidin binding in the cortex by detaching different layers of the surface complex from each other. Since localization of F-actin in ciliates has raised a considerable amount of dispute in the past, we also repeated all these experiments with RITC-labeled HMM, but we obtained essentially the same labeling pattern as with R-phalloidin. Ciliary basal bodies therefore clearly contain some F-actin. Our data shed some light on aspects of surface structuring and motility in these cells.

Actin Cytoskeleton↗
PubMed1986

Filamentous actin in paramecium cells: functional and structural changes correlated with phalloidin affinity labeling in vivo.

Rhodaminylated (R)-phalloidin microinjected into Paramecium tetraurelia cells at a final concentration of greater than or equal to 20 micrograms/ml produces considerable functional and structural changes. F-actin bundles (with 20 micrograms/ml phalloidin within 15 min) are formed, which subsequently (greater than 30 min) are sequestered into autophagic vacuoles; simultaneously, the originally intense fluorescence of a narrow cortical layer becomes more and more diminished. When such microinjected cells are processed for electron microscopy, they display concomitant ultrastructural alterations, namely, the formation of transcellular bundles of 5-7 nm-thick filaments, which subsequently appear in autophagosomes, as well as a considerable reduction of filamentous materials in the cortex. This, in turn, entails a considerable restructuring of the cortex, enabling free access of various structural components to the cortex. Higher doses of R-phalloidin abolish cytoplasmic streaming (e.g., 50 micrograms/ml after 20-30 min); although the cells may survive, new secretory organelles (trichocysts) are no longer docked to the cell membrane. In contrast, exocytosis of docked trichocysts (as well as subsequent membrane resealing and retrieval) is not impaired under any conditions. Cortical F-actin may account for the cytoplasmic streaming that may normally guarantee the delivery of new trichocysts to free docking sites at the cell membrane. When docking is inhibited by high R-phalloidin doses, excess free trichocysts are sequestered into autophagosomes (crinophagy). One of the most sensitive cell functions is food vacuole formation (assayed by prelabeling with India ink), which correlates with the presence of R-phalloidin labeling in the cytostomal region and around food vacuoles. The main conclusions from this work are that filamentous actin may be involved in structuring of the cortex and in cytoplasmic streaming, and may therefore influence the formation, and possibly the transcellular transport (cyclosis), of food vacuoles, as well as the docking of trichocysts, whereas it does not play a role in exocytosis per se or in the steps immediately following.

Actin Cytoskeleton↗
PubMed1985

Synchronous exocytosis in Paramecium cells involves very rapid (less than or equal to 1 s), reversible dephosphorylation of a 65-kD phosphoprotein in exocytosis-competent strains.

Synchronous exocytosis in Paramecium cells involves the rapid (less than or equal to 1 s) dephosphorylation of a 65-kD phosphoprotein, which, after a lag phase of approximately 5 s, is reversed within approximately 20 s. Exocytosis inhibitors suppress this reaction; stimulatory and inhibitory effects are dose dependent. The dephosphorylation of the 65-kD phosphoprotein occurs only in exocytosis-competent strains, but not in mutant strains that cannot carry out membrane fusion, or that are devoid of secretory organelles or cannot transport them to the cell membrane. Since under all conditions analyzed the transient dephosphorylation of the 65-kD phosphoprotein strictly parallels the actual amount of exocytosed organelles, this process might be involved in exocytosis performance, perhaps in its initiation.

Animals↗
PubMed1985

Synchronous exocytosis in Paramecium cells. VI. Ultrastructural analysis of membrane resealing and retrieval.

After the synchronous induction of exocytosis of secretory organelles (trichocysts) in Paramecium tetraurelia cells the process of membrane resealing and retrieval could be followed under synchronous conditions. The characteristic aggregates of membrane intercalated particles (MIPs) contained within the freeze-fractured cell membrane (rings and rosettes) and trichocyst membranes (annulus MIPs), in addition to collar striations on the top of trichocyst membranes, served as endogenous ultrastructural markers. This allowed us to follow the re-arrangement of membrane constituents during and after exocytosis with high temporal and spatial precision. Membrane specificity is maintained to a considerable extent (approximately 99.5%), as judged from the rare occurrence of aberrant resealing (according to freeze-fracture data) and from the rather minute shift of glycocalyx components (according to electron staining experiments) during normal membrane resealing. Coated pits are not involved in membrane retrieval (155 ghosts analysed); since the membrane regions involved in exocytotic fusion are backed by apposed materials, probably proteins, this may restrain membrane constituents from intermixing. Another factor for maintaining membrane specificity is the fact that resealing of the exocytotic opening occurs much more rapidly than in most other systems. The retrieval operates with a half-life of 3 (strain 7S) to 9 min (K401); the involvement of cortical microtubules in the retrieval can be largely excluded, since only two microtubules (of unidentified origin) were seen to approach ghost structures in 4074 cases analysed during this period of intense ghost retrieval. Phalloidin microinjected at a dose that blocked all cytoplasmic streaming (before synchronous exocytosis was induced) did not abolish membrane resealing and retrieval, which, therefore, may be passive processes.

Animals↗
PubMed1985

Synchronous exocytosis in Paramecium cells. IV. Polyamino compounds as potent trigger agents for repeatable trigger-redocking cycles.

We found that different polyamino compounds trigger the instantaneous and simultaneous release of trichocysts from Paramecium tetraurelia cells (monoxenically bacterized cultures), provided amino groups are spaced in intervals of approximately 1.0 nm; in this case even diamines or oligopeptides exert some trigger effect. The most potent trigger agent found was aminoethyldextran (AED, MW = 40 kDa) which was used mainly as a derivative with 40 -NH2/molecule. A maximal response (strain K401) was achieved at 1.38 X 10(-6) M, a half maximal response at 1.08 X 10(-6) M. AED acts by a dual effect, i.e., not only by statistically properly spaced amino groups but also by some additional effect of the dextran molecule, since this greatly enhances the effect of oligoamines, although it exerts no trigger effect per se. From a total of approximately 1120 or approximately 1230 trichocysts per cell (strain K401 or 7S) approximately 95% are releasable by AED. In these strains the number of non-releasable trichocysts corresponds closely to the number of undocked trichocysts floating in the cytoplasm, so that practically all trichocysts which are docked to the cell membrane, can be released. (We also analysed different mutant strains for their response to AED.) Massive trichocyst release does not impair cell viability or culture growth, and multiple release-redocking cycles can be performed; up to 5 trigger-docking cycles were tested with individual cells in 12 h intervals. AED-triggered exocytosis requires a free extracellular [Ca2+] of greater than or equal to 10(-5) M; it is inhibited by EGTA (ethyleneglycol-bis(beta-aminoethyl ether)-N,N'-tetraacetate), by a short pH 5.5 shock or by neomycin at 10(-5) M concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Synchronous exocytosis in Paramecium cells. V. Ultrastructural adaptation phenomena during re-insertion of secretory organelles.

We used aminoethyldextran (AED) as a secretagogue for the simultaneous exocytosis of a great proportion of secretory organelles (trichocysts) from Paramecium tetraurelia cells and we applied freeze-fracturing and ultrathin sectioning for a quantitative analysis of the re-arrangement of ultrastructural details within the cell membrane during re-insertion of new trichocysts. Characteristic arrangements of membrane-intercalated particles (MIPs) occur over trichocyst docking sites: 300 nm large double rings of MIPs and a MIP rosette in the middle. Empty sites, displaying a compressed ring ("parenthesis") without a rosette, are expanded to full size rings when a trichocyst is docked. We obtained a first hint on the possible existence of a short lived (approximately 5 min) adaptation stage, represented by rings without a rosette. This could mean that docking of a trichocyst would induce the assembly of rosette MIPs over a newly docked trichocyst. The reformation of rosettes is paralleled by an increasing number of extrudable trichocysts which underscores the causal role of rosette MIPs in exocytosis performance. New trichocysts are inserted at the old predetermined sites after removal of ghosts and formation of a "plug" as a receptor-type structure. The number of non-docked, free trichocysts in the cytoplasm is only slightly changed, indicating a continuous synthesis and docking rate (approximately 2-3 organelles per min). Since in strain 7S ghosts are removed within approximately 10 min and docking goes on over 9 h, there occur many empty docking sites in the time period in between, with a maximum of approximately 1 h after AED triggering, thus providing a unique situation for further experiments.

Adaptation, Physiological↗
PubMed1984

Synchronous exocytosis in Paramecium cells. I. A novel approach.

From a total number of approximately 1100-1300 secretory organelles ("trichocysts") in a Paramecium tetraurelia cell, approximately 90% are docked to the cell membrane. Approximately 90% of this subpopulation can be discharged from the cells within seconds, when exposed to the novel trigger agent aminoethyldextran (AED) at a concentration of 10(-6) M. No deleterious side effects were recognized with this trigger agent even over long time periods. By application of AED close to cells with the use of a micropipette we found that triggering of trichocyst release by AED involves a local, non-propagated effect and that all regions of the cell body are equally reactive. It requires exogenous Ca2+. It is independent of ciliary Ca2+ channels, since deciliated cells or ciliary mutations with "Ca2+-tight" cilia respond to AED with normal exocytosis performance. The massive and rapid occurrence of trichocyst release in response to AED allowed for a freeze-fracture analysis of intramembraneous changes (see Olbricht et al., Exp cell res 151 (1984) 14 [23]) which also shows the involvement of exocytosis) as well as for a long-term study of the re-attachment of trichocysts (see Haacke & Plattner, Exp cell res 151 (1984) 21 [10]) under synchronous conditions.

Animals↗
PubMed1984

Synchronous exocytosis in Paramecium cells. II. Intramembranous changes analysed by freeze-fracturing.

Since Paramecium tetraurelia cells were found to discharge synchronously most of their secretory organelles ('trichocysts') when exposed to 10(-6) M aminoethyldextran (AED) [17], this was now used for a freeze-fracture and -etching analysis of intramembranous changes during exocytosis performance, in conjunction with a rapid freezing method. In controls the potential exocytosis sites of the cell membrane revealed a 'rosette' of approximately 8 membrane-intercalated particles (MIPs) within a 300 nm large double 'ring' of MIPs (see [18]). During exocytosis we found the following changes: (a) Membrane fusion starts as a focal event, the smallest recognizable openings measuring 20-30 nm in diameter. (b) The exocytotic opening always forms in the center of the rosette. (c) Rosette MIPs may stay very close to the exocytotic opening, or they may partly be dispersed as the exocytotic opening is formed. (d) No diaphragm is formed during exocytotic membrane fusion. (e) The exocytotic opening is increasing to a size where it fills the total fusogenic zone contained within a ring, but not any further. (f) Rosette MIPs become further dispersed through the rings. (g) Resealing involves the transformation of rings into a collapsed form ('parenthesis'). (h) A resealed exocytosis site contains no conspicuous MIP aggregates, such as rosettes or 'annulus' structures from the trichocyst membrane, indicating a clear separation of both components.

Animals↗
PubMed1984

Synchronous exocytosis in Paramecium cells. III. Rearrangement of membranes and membrane-associated structural elements after exocytosis performance.

Aminoethyldextran (AED) was used to trigger the synchronous release of trichocysts from Paramecium tetraurelia cells (see [8]) by a mechanism involving exocytotic membrane fusion and resealing (see [5]). Ultrastructural changes were analyzed by quantitative evaluation of ultrathin sections. In resting cells the percentage of potential trichocyst-docking sites which are actually occupied by a trichocyst was 58%; 36% of potential docking sites contained ghosts and 6% a "plug" of electron-dense material. We derived from our data that paramecia would discharge permanently and spontaneously trichocysts (without AED) at a rate of 2-3 per min (which we then also verified by counting the spontaneous release rate) and that this value is equivalent to the docking rate. For the synchronous expulsion of trichocysts in response to AED we had determined that the degree of synchrony is more than a hundred times better than in most other systems (see [8]). We have determined the half-lives (HL) for different events involved in exocytosis and re-docking as follows: approximately 3 sec for trichocyst discharge, approximately 3 sec for the formation of ghosts, 8 min for the clearing of ghosts from the cell surface, 4 min for the formation of "plugs". Trichocysts are docked with a HL of 40 min and "plugs" (considered as receptor-type structures for trichocyst docking) disappear with a concomitant HL of 50 min. Evidently the clearing of ghosts allows for re-formation of "plugs" but the respective HL values signal that "plugs" may also be formed anew. The relatively slow decline of the percentage of "plugs" (after their azimuth 15 min after AED triggering) may also indicate the synthesis of new docking sites. After a period of over approximately 3 h following AED triggering, the original situation is roughly re-established and maintained over the whole period of population growth analyzed.

Animals↗
PubMed1984

The secretory contents of Paramecium tetraurelia trichocysts: ultrastructural--cytochemical characterization.

The secretory contents ("matrix") of Paramecium tetraurelia trichocysts expand by a factor of 4.5 when they undergo a Ca2+-mediated decondensation in the course of exocytosis. This is paralleled by a concomitant increase in the interval of the periodic banding of the matrix from 12 nm to 45-51 nm, which becomes visible with different electron stains for proteins and negatively charged groups. Recent reports of actin in secretory contents led us to investigate its redistribution and artifactual adsorption to the trichocyst contents upon their expansion. To visualize this effect we used peroxidase-labeled F(ab) fragments from an IgG directed against Paramecium actin, a DNAase I-gold complex, and the induction of F-actin polymerization. The trichocysts were analyzed in situ as well as after isolation by density-gradient centrifugation. Additionally, in response to current reports in the literature, we reanalyzed trichocyst contents for any possible presence of calmodulin. We applied three independent in situ methods for this: autofluorescence after trifluoperazine affinity labeling, calmodulin-fluorescence affinity labeling, and an electron microscopic immunocytochemical method. All three methods failed to reveal any significant labeling of structurally intact trichocysts in situ, although we also showed that discharged trichocysts avidly adsorb calmodulin from the culture medium. From the present data we conclude that the decondensation of trichocysts during exocytosis is mediated by a sudden conformational rearrangement of secretory proteins in the trichocyst contents, without the involvement of any other regulatory or contractile proteins, which occur only in the cytoplasm. Trichocyst contents are not significantly--if at all--glycosylated.

Actins↗
PubMed1983

Decoupling of exocytotic membrane fusion from protein discharge in Paramecium cells.

Under certain conditions it is possible in Paramecium cells to induce selectively the fusion of the secretory organelle membrane with the cell membrane without the involvement of any further steps (release of secretory contents, etc.). A Ca2+-mobilizing fusogen was used in the presence of components which inhibit the discharge of the secretory contents (Mg2+ and EGTA, mainly). One can thus produce many exocytotic openings with the secretory contents (which are normally vigorously discharged) still retained.

Dibucaine↗