Infection of algae-free Paramecium bursaria with symbiotic Chlorella sp. isolated from green paramecia

1989 ◽  
Vol 93 (3) ◽  
pp. 571-579
Author(s):  
RENATE MEIER ◽  
WOLFGANG WIESSNER
Keyword(s):  
Algal Cell ◽  
Middle Part ◽  
Paramecium Bursaria ◽  
Middle Region ◽  
Free Medium ◽  
Large Vacuole ◽  
Chlorella Sp ◽  
The Moment ◽  
In Cells

Algae-free Paramecium bursaria was exposed to cells of Chlorella sp. for 30s (pulse) and then incubated in algae-free medium for periods between 0 and 15 min. During this chase the fate of the vacuoles formed during the exposure to algae was followed in order to reveal the moment of perialgal vacuole (PV) formation. PVs are characterized by always enclosing an individual algal cell and thus differ from digestive vacuoles (DVs). PVs did not appear immediately after the pulse, but were found only in cells chased for at least 3 min. In those ciliates the algae-containing vacuoles were more than 3 min old and located in the middle part of the cell. These results showed that PVs were not formed directly at the cytopharynx, but many algae were at first enclosed together in large DVs. After the release from the cytopharynx DVs undergo a sequence of fusion events during their cyclosis: fusion with acidosomes apparently occurs at the cell's posterior end, not later than 2 min, and fusion with lysosomes in the middle region of the cell at the earliest at about 7 min, after the pinching off of a DV from the cytopharynx. Thus, PVs appeared to develop from condensing DVs after acidosomal but before lysosomal fusion. As the first step, part of the DV enclosing an individual algal cell must detach from the large vacuole. Further steps and the implications of the mechanism of PV formation resulting in the re-establishment of endosymbionts in P. bursaria are discussed.

Comparative freeze-fracture study of perialgal and digestive vacuoles in Paramecium bursaria

1984 ◽  
Vol 71 (1) ◽  
pp. 121-140
Author(s):  
R. Meier ◽  
M. Lefort-Tran ◽  
M. Pouphile ◽  
W. Reisser ◽  
W. Wiessner
Keyword(s):  
Algal Cell ◽  
Freeze Fracture ◽  
Paramecium Bursaria ◽  
Digestive Vacuole ◽  
Intimate Contact ◽  
Chlorella Sp ◽  
Membrane Topography ◽  
Long Time ◽  
Membrane Changes ◽  
Endocytic Activity

In the endosymbiotic unit of Paramecium bursaria (Ciliata) and Chlorella sp. (Chlorophyceae) algae are enclosed individually in perialgal vacuoles, which do not show acid phosphatase activity and thus differ from digestive vacuoles. Both types of vacuoles have been studied by freeze-fracture. Perialgal vacuoles are nearly spherical; their membrane always fits tightly to the algal surface. The vacuole size and shape do not vary much. During division of the algal cell into four autospores the vacuole diameter only doubles. After autospore formation the vacuole invaginates around the algal daughter cells and divides. Newly formed perialgal vacuoles remain in intimate contact and exhibit characteristic attachment zones before final separation. The two fracture faces of perialgal vacuole membranes are homogeneously covered with intramembranous particles (IMPs) but rarely show signs of vesicles pinching off or fusing with the membrane, except during vacuole division. The P-faces bear more IMPs (3164 +/− 625 IMP/micron 2) than the E-faces (654 +/− 208 IMP/micron 2). The range of IMP density on both faces is enormous, suggesting that the membrane is not static. Membrane changes are supposed to occur simultaneously with the enlargement of the vacuole and to be caused by fusion with cytoplasmic vesicles, as the fractured necks on vacuole membranes may indicate. Digestive vacuoles in P. bursaria show significant variations in size, shape, membrane topography and IMP density, as well as signs of endocytic activity. Different vacuole populations are present in P. bursaria according to different feeding conditions: ciliates fed for a long time have small vacuoles with few IMPs (322 +/− 198 IMP/micron 2 on the E-faces, 1438 +/− 458 IMP/micron 2 on the P-faces), which are probably condensed digestive vacuoles, whereas organisms fed for a short time have larger vacuoles with highly particulate faces (680 +/− 282 IMP/micron 2 on the E-faces, 2701 +/− 503 IMP/micron 2 on the P-faces) and thus are supposed to be older vacuoles. The digestive vacuole membrane changes continuously. Compared to digestive vacuoles perialgal vacuoles are characterized by small size combined with high IMP density on the two fracture faces. Their IMP densities resemble those of old digestive vacuole membranes. However, it would be premature to conclude that membranes of perialgal and old digestive vacuoles are identical. Membranes of old digestive vacuoles are mainly derived from lysosomal material, which presumably does not contribute to the formation of perialgal vacuole membranes as is indicated by the small vacuole diameter; fusion with lysosomes would considerably enlarge it.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Trypsin-induced increase in cyclic AMP concentration in rat thymocytes An effect independent of calcium and calmodulin

1986 ◽  
Vol 239 (3) ◽  
pp. 603-607 ◽  
Author(s):  
J Segal
Keyword(s):  
Cyclic Amp ◽  
Free Medium ◽  
Standard Medium ◽  
Intracellular Pool ◽  
Calmodulin Inhibitor ◽  
Related Increase ◽  
In Cells

Trypsin produces a dose-related increase in cellular cyclic AMP concentration in rat thymocytes [Shneyour, Patt & Trainin (1976) J. Immunol. 117, 2143-2149; Segal & Ingbar (1983) Clin. Res. 31, 277A]. In the present study, I examined whether this effect of trypsin requires Ca2+ and whether it is modified by calmodulin. In fresh thymocytes suspended in standard medium (containing 1 mM-Ca2+), trypsin produced a concentration-dependent increase in cytoplasmic free Ca2+ concentration, which was evident at a concentration of 50 micrograms of trypsin/ml and reached maximal values at about 1 mg/ml. This effect of trypsin was very prompt in onset, almost immediate, and reached maximal values within 2-3 min. But in cells suspended in essentially Ca2+-free medium (6 nM free Ca2+), trypsin had no effect on cytoplasmic free Ca2+ concentration, which indicates that trypsin acted by increasing Ca2+ uptake rather than Ca2+ release from an intracellular pool. However, the increase in thymocyte cyclic AMP concentration produced by trypsin was independent of extracellular Ca2+ and was not influenced by calmodulin, because it was the same in the presence or absence of Ca2+ and was not changed by the calmodulin inhibitor trifluoperazine. I therefore suggest that in rat thymocytes the trypsin-induced increase in cyclic AMP concentration does not require Ca2+ and is not influenced by calmodulin.

Plastic-Wave Propagation Effects in Transverse Impact of Membranes

1960 ◽  
Vol 27 (1) ◽  
pp. 172-176 ◽  
Author(s):  
B. Karunes ◽  
E. T. Onat
Keyword(s):  
Unique Solution ◽  
Average Rate ◽  
Initial Energy ◽  
Plane Motion ◽  
Middle Region ◽  
Bending Rigidity ◽  
Transverse Impact ◽  
Significant Information ◽  
Subsequent Motion ◽  
The Moment

The paper is concerned with the plane motion of a rigid-strain-hardening membrane attached to two parallel fixed supports. The membrane is subjected to a uniformly distributed transverse impulse and the subsequent motion of the membrane is to be determined with the particular emphasis on the variation of thickness in the final deflected shape. It is first shown that two essentially different initial modes of deformation exist depending on the average rate of hardening. For both modes, the analysis can be based on two types of waves of discontinuity until the moment when the compressive membrane forces occur in the middle region of the membrane. The presence of compressive forces will generally preclude the existence of a unique solution for further motion. The bending rigidity will probably have to be included into the analysis in order to obtain a unique solution. However, for the technically important rates of hardening and velocities, the kinetic energy of the membrane at the moment of occurrence of compressive forces is small compared with the initial energy, so that significant information could be obtained from the present analysis about the variation of thickness and hardening throughout the membrane.

scholarly journals Agonist-induced Ca2+ influx in human neutrophils is secondary to the emptying of intracellular calcium stores

1991 ◽  
Vol 277 (1) ◽  
pp. 73-79 ◽  
Author(s):  
M Montero ◽  
J Alvarez ◽  
J Garcia-Sancho
Keyword(s):  
Plasma Membrane ◽  
Intracellular Calcium ◽  
Time Course ◽  
Human Neutrophils ◽  
Calcium Stores ◽  
Free Medium ◽  
Prolonged Incubation ◽  
Intracellular Calcium Stores ◽  
Cytochrome P 450 ◽  
In Cells

Emptying of the intracellular calcium stores of human neutrophils, by prolonged incubation in Ca(2+)-free medium, by treatment with low concentrations of the Ca2+ inophore ionomycin, or by activation with cell agonists, increased the plasma-membrane permeability to Ca2+ and Mn2+. The chemotactic peptide formylmethionyl-leucyl-phenylalanine and the natural agonists platelet-activating factor and leukotriene B4 released different amounts of calcium from the stores and induced Ca2+ (Mn2+) uptake, the rate of which correlated inversely with the amount of calcium left in the stores. The increased Mn2+ uptake induced by these agonists was persistent in cells incubated in Ca(2+)-free medium, but returned to basal levels in cells incubated in Ca(2+)-containing medium, with the same time course as the refilling of the calcium stores. The calcium-stores-regulated Mn2+ influx, including that induced by agonists, was prevented by cytochrome P-450 inhibitors. We propose that agonist-induced Ca2+ (Mn2+) influx in human neutrophils is secondary to the emptying of the intracellular stores which, in turn, activates plasma-membrane Ca2+ channels by a mechanism involving microsomal cytochrome P-450, similar to that described previously in thymocytes [Alvarez, Montero & Garcia-Sancho (1991) Biochem. J. 274, 193-197].

[Na]i modulates isoproterenol's effect on Ca permeability in cultured heart cells

1987 ◽  
Vol 253 (2) ◽  
pp. C253-C262 ◽  
Author(s):  
D. Kim ◽  
T. W. Smith
Keyword(s):  
Resting Membrane Potential ◽  
Heart Cells ◽  
Ca Channel ◽  
Control Medium ◽  
Free Medium ◽  
Cardiac Muscle Cells ◽  
45Ca Uptake ◽  
Ca Uptake ◽  
Chick Heart ◽  
In Cells

Isoproterenol (ISO) augments the slow inward Ca current in cardiac muscle cells. We examined the role of intracellular Na (Nai) on ISO-mediated alterations in Ca uptake in cultured chick heart cells. In 140 mM Na medium, 1 microM ISO did not measurably alter 45Ca uptake. When cells were first preincubated in Na-free medium for 5 min and then incubated in control medium with 45Ca, ISO increased 45Ca uptake by 30%. Nifedipine (10 microM), verapamil (1 microM), or dl-propranolol (1 microM) abolished the effect of ISO on 45Ca uptake. CGP 28392 (1 microM), a Ca channel agonist, increased Ca influx in a manner that was augmented by decreased Nai, similar to the ISO response. Neither ISO nor CGP 28392 altered 45Ca uptake when cells preincubated in Na-free medium were further incubated in Na-free medium containing 45Ca. Exposure of cells to Na-free medium or 25 mM K+ medium caused depolarization of the resting membrane potential to approximately -40 mV. In the absence of ISO, the 45Ca uptake in cells preincubated in Na-free or 25 mM extracellular K (Ko) medium was significantly greater than in cells preincubated in control medium. This appeared to be due partly to increased 45Ca uptake via nifedipine-sensitive pathways. These findings support the hypothesis that reduction in Nai concentration ([Na]i) enhances the ISO-induced augmentation of Ca uptake via nifedipine-sensitive pathways (presumably via slow Ca channels), probably by a direct effect on the channels.

scholarly journals STUDY OF THE ENZYMATIC STAGE OF MILK GELATION: CHANGES IN VISCOSITY AND MICROSTRUCTURE

Food systems ◽  
2019 ◽  
Vol 2 (3) ◽  
pp. 4-8
Author(s):  
I. T. Smykov
Keyword(s):  
Phase Transition ◽  
Statistical Processing ◽  
Middle Part ◽  
Gel Point ◽  
Casein Micelles ◽  
Viscosity Change ◽  
Research Results ◽  
Milk Coagulation ◽  
Milk Gelation ◽  
The Moment

The article presents the results of experimental joint studies of changes in the viscosity and microstructure of milk at the enzymatic stage of gelation. Based on the statistical processing of the array of research results, it was determined that the viscosity change at this stage is not monotonic, as it is usually stated, but two-stage in the middle part and S-shaped, preceding the gel point, at its end. It was found that the S-shaped change in viscosity at the end of the enzymatic stage of milk coagulation coincides with changes in the microstructure of casein micelles and reflects the existence of a cooperative conformational phase transition in casein molecules of micelle clusters. A description of the possible mechanism of this phase transition is proposed. It was noted that the moment of the S-shaped change in the milk viscosity at the enzymatic gelation stage and the corresponding cooperative phase transition in casein micelles are a physical reflection of the gel point. The research results provide a better understanding of the mechanism of enzymatic coagulation of milk in a cheesemaking tank.

scholarly journals Sådan fortæller man, at man får et barn. Diskursive onlinekonstruktioner

2012 ◽  
Vol 40 (113) ◽  
pp. 63-78
Author(s):  
Anette Grønning
Keyword(s):  
Pregnant Woman ◽  
Family Relations ◽  
Newborn Baby ◽  
Middle Region ◽  
Presentation Of Self ◽  
Public And Private ◽  
Self Presentation ◽  
Family Ties ◽  
The Family ◽  
The Moment

HOW TO TELL THAT YOU ARE PREGNANT | The focus of this article is mediated exposure of life before life based on fetal images, including textual updates uploaded to individual Facebook profiles. The article analyses how pictures of embryos have become part of daily digital self presentation and the narrative about expecting a child. We follow a pregnant’s Facebook profile from the moment she uploads the first fetal image around the twelfth week, till the moment she updates with the news about the delivery documented by a picture of her newborn baby. The mediated exposure also involves the coming father, as the pregnant woman tags the pictures with his name to underline the family ties. Many relations (mostly women) contribute with comments that can be categorised into three groups: serious, humoristic-ironic and analysing questioning. The Facebook update can be seen as a side stage or middle region (Meyrowitz) position, a constantly more muddy space between public and private self presentation. This new praxis confirms Jean Baudrillard’s thoughts about the subject’s exaggerated presentation of self. The online audience is more comprehensive and less controllable than offline. The pregnant exposes her pregnancy, motherhood and her product (the foetus)through updates, pictures and tagging. The Facebook update is a new way to interpellate family relations and to celebrate the coming new member with the comprehensive network in three levels.

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