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C Sardet

Publications and source records attributed to C Sardet.

At least 91 records · Page 5Linked to original sources
PubMed1988

Protein and lipid utilization during long-term fasting in emperor penguins.

The body mass of male emperor penguins is approximately 38 kg at the beginning of the 4-mo winter fast connected with breeding, and it is an estimated approximately 18 kg in leanest birds at time of spontaneous refeeding. For a 38- to 18-kg range, we investigated the changes in the rate of body mass loss, body composition, and plasma concentrations of uric acid and urea. After the first few days (phase I) a steady state (phase II) was reached in the proportions of the energy derived from proteins and lipids with proteins accounting for a constant 4%, and the remaining 96% being from lipids. The same proportions were maintained until body mass had decreased to 24 kg. Below this value the proportion of energy derived from proteins increased progressively (phase III), being 14 times higher at 18 kg than during phase II. Rate of body mass loss and plasma uric acid and urea concentrations closely reflected the changes in protein utilization: being at a low and steady value throughout phase II and increasing during phase III. Emperor penguins also fast during the spring, but for periods of only 2-3 wk. We found a 2.5 times higher value for rate of body mass loss, uric acid, and urea during spring phase II, suggesting lower effectiveness in protein sparing at that time. It may be attributed to the lower initial lipid reserves of spring birds. Would these findings be generalized to the wide variety of birds and mammals that spontaneously fast under natural conditions?(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1988

The human amiloride-sensitive Na+/H+ antiporter: localization to chromosome 1 by in situ hybridization.

The Na+/H+ antiporter is a ubiquitous membrane-bound enzyme involved in pH regulation of vertebrate cells. We cloned the human gene capable of complementing antiporter-deficient mouse fibroblasts and isolated an exon-containing genomic DNA fragment. Using this genomic probe, we mapped the putative structural gene of the amiloride-sensitive Na+/H+ antiporter to the human chromosome region 1p35----p36.1 by in situ hybridization.

Carrier Proteins↗
PubMed1985

A marker of animal-vegetal polarity in the egg of the sea urchin Paracentrotus lividus. The pigment band.

We have examined the subequatorial accumulation of pigment granules (the so-called 'pigment band') in the egg of the sea urchin Paracentrotus lividus, which constitutes an unambiguous marker of animal-vegetal polarity. Most of the reddish pigment granules are situated at the periphery of the egg. They exhibit occasional saltatory movements and can aggregate into large patches. Pigment granules are retained as a band in the isolated cortex when the egg surface complex is isolated by shearing eggs attached to polylysine-coated surfaces with calcium-free isotonic solutions. Pigment granules remain as the main vesicular component of fertilized egg cortices or of unfertilized egg cortices perfused with calcium to provoke cortical granule exocytosis. They may be anchored to the isolated cortex through associations with the plasma membrane and with an extensive subsurface network of rough endoplasmic reticulum (rough ER). Pigment granules contain antimonate-precipitable calcium and, in this respect and many others, resemble acidic vesicles recently identified in the cortex of unpigmented sea urchin eggs. We discuss the similarities observed between granules and acidic vesicles in various urchin egg species and their possible functions.

Actin Cytoskeleton↗
PubMed1985

Exocytosis of sea urchin egg cortical vesicles in vitro is retarded by hyperosmotic sucrose: kinetics of fusion monitored by quantitative light-scattering microscopy.

We have used the isolated planar cortex of sea urchin eggs to examine the role of osmotic forces in exocytosis by morphological and physiological methods. Electron micrographs of rotary-shadowed replicas show an en face view of exocytosis and demonstrate fusion of cortical vesicles to the underlying oolemma upon addition of calcium. Freeze-fracture replicas of rapidly frozen cortices reveal specialized attachment sites between cortical vesicles and the oolemma, and between the cortical vesicles themselves. We describe a novel light scattering assay for the kinetics of fusion which allows rapid changes of solutions and monitors exocytosis in real time. The rate and extent of fusion are found to be calcium dependent. The removal of calcium halts exocytosis. The validation of exocytosis in this system and development of tools for kinetic analysis allowed us to test predictions of the osmotic hypothesis of exocytosis: hyperosmotic media should inhibit exocytosis; calcium should cause vesicular swelling. Cortical vesicles were found to be permeant to sucrose, glucose, and urea. In media made hyperosmotic with 1.7 M sucrose, cortical vesicles were seen to shrink. Addition of calcium in hyperosmotic media led to a 10-fold decrease in the rate of exocytosis compared with the isotonic rate. The rate, while triggered by calcium, was no longer calcium-dependent. This slowing of exocytosis allowed us to photograph the swelling of cortical vesicles caused by calcium. Removal of calcium had no effect on subsequent exocytosis. Return of cortices to isotonic medium without calcium led to immediate exocytosis. These results are consistent with the idea that swelling of cortical vesicles is required for fusion of biological membranes.

Animals↗
PubMed1984

Tracing of cell lineage in embryonic development of Phallusia mammillata (Ascidia) by vital staining of mitochondria.

Vital staining of mitochondria with a fluorescent dye 3,3'-diethyloxacarbocyanine was used to follow cell lineage in embryos of Phallusia mammillata. The results agree in general with the plan established by Conklin in 1905. Strong fluorescence migrated after fertilization similarly to the pigment of the "yellow crescent" in Styela. Later, fluorescence segregated into muscle cell primordia, but not into mesenchyme cells. An animal hemisphere cell, b 8.17 also exhibited strong fluorescence and joined a group of muscle primordia, very likely becoming a muscle cell itself. In the tadpole, all the tail muscle cells were fluorescent. Fluorescence was also noticed in nerve cell primordia of the vegetal hemisphere, particularly in the cell A 8.16 whose descendants appeared to become part of the sensory vesicle which was strongly fluorescent in the tadpole. The usefulness of this type of vital staining in following cell lineage of colorless embryos is stressed.

Animals↗
PubMed1984

Fertilization and early development in Beroe ovata.

Fertilization in the clear egg (1 mm in diameter) of the ctenophore Beroe ovata and, in particular, the positioning and movements of pronuclei, and their relationship to the larval oral-aboral axis have been observed. Fertilization can take place anywhere on the egg surface. The sperm pronucleus remains at its entry site and becomes surrounded by a specialized zone (30-50 micron in diameter) beneath the surface referred to as the sperm pronuclear zone or SPZ and devoid of large cortical granules. Polyspermy has been observed to be frequent; each pronucleus is surrounded by its own SPZ. Only the egg pronucleus migrates with a continuous velocity (averaging 18 micron/min) and moves beneath the surface directly toward the immobile sperm pronucleus. In polyspermic eggs, the egg pronucleus can probe several SPZ, each containing a single sperm nucleus, before it finally enters one SPZ and fuses with the chosen sperm pronucleus. These migrations of the egg pronucleus occur over several millimeters and take hours, but the mechanism underlying the motion or how the egg pronucleus decides which SPZ to enter is not yet known. Under our experimental conditions the mitotic apparatus and the first cleavage plane which defines the oral-aboral axis of the larva (see Reverberi (1971). "Experimental Embryology of Marine and Fresh-Water Invertebrates." North-Holland, Amsterdam. for review) pass through the point of sperm entry. During fertilization and cleavage, movements of a cortical autofluorescent material are clearly seen. This material is segregated into micromeres as cleavage progresses.

Animals↗
PubMed1984

The ultrastructure of the sea urchin egg cortex isolated before and after fertilization.

The three-dimensional organization of cortices isolated from unfertilized and fertilized Strongylocentrotus purpuratus eggs has been examined by several techniques of light and electron microscopy. It has been found that when moderate shear forces are used, the isolated unfertilized egg cortex, in addition to cortical granules, contains acidic vesicles and an elaborate network of rough endoplasmic reticulum. This network provides a physical link between the cell surface and several kinds of cytoplasmic organelles (mitochondria, yolk granules, acidic vesicles) which are retained as part of the isolated cortex when gentle shear forces are applied. Furthermore a good visualization of actin in the cortex is provided: it is present as short filaments and mostly within the stubby microvilli of the egg. Finally, it has been noted that plaques exist on the inside face of the plasma membrane ready to assemble into typical clathrin coats that prefigure the burst of coated vesicle endocytosis that takes place after fertilization. The cortex isolated soon after fertilization is shown to contain coated pits and a scaffolding of filaments (mostly actin) in which many acidic vesicles are embedded.

Animals↗
PubMed1984

A specific mutation abolishing Na+/H+ antiport activity in hamster fibroblasts precludes growth at neutral and acidic pH.

A H+-suicide technique based on the reversibility of Na+/H+ antiport was developed for the selection of mutants deficient in this membrane-bound activity. The strategy was to use the Na+/H+ antiporter as a H+-vector killing device. Chinese hamster lung fibroblasts (CCL39) were loaded with LiCl and incubated in Na+-, Li+-free choline Cl saline solution (pH 5.5). Under these conditions, intracellular pH dropped in 5 min from 7.1 to 4.8, leading to a rapid loss of cell viability (less than 0.1% survival after 30 min). Cytoplasmic acidification and cell death were prevented by treatment with 5-N,N-dimethylamiloride, a potent inhibitor of Na+/H+ antiport. Of the H+-suicide resistant clones that survived two cycles of selection, 90% were found deficient in Na+/H+ antiport activity. One class of mutants (PS10, PS12) fully resistant to the H+-suicide test, does not acidify the cell interior in response to an outward-directed Li+ gradient and has no detectable amiloride-sensitive Na+ influx measured either in Li+- or H+-loaded cells. Growth of these fibroblast clones lacking Na+/H+ antiport was found to be pH conditional in HCO3(-)-free medium. Whereas wild-type cells can grow over a wide range of external pHs (6.6-8.2), PS mutants cannot grow at neutral and acidic pHs (pH less than 7.2); their optimal growth occurs at alkaline pH values (pH 8-8.3). These findings strongly suggest that the Na+/H+ antiport activity through regulation of intracellular pH plays a crucial role in growth control.

Acid-Base Equilibrium↗
PubMed1982

Changes in intracellular cations following fertilization of sea urchin eggs. Na+/H+ and Na+/K+ exchanges.

Sodium and potassium contents, as well as H+ excretion were measured at various times after fertilization in eggs of the sea urchin Paracentrotus, using a rapid filtration technique (Payan, P, Girard, U P, Christen, R & Sardet, C, Exp cell res 134 (1981) 339 [1]). Sodium content changes with a biphasic time course due to the appearance of two exchange mechanisms: 1. A transient Na+/H+ exchange with a l/l stoichiometry causes a rapid rise in intracellular sodium. This exchange lasts about 3 min. and is not inhibited by poisoning the eggs with NaCN. 2. An Na+/K+ exchange, detectable within minutes of fertilization causes sodium content of the egg to fall and settle below unfertilized level. This exchange is energy-dependent, reduced in low K+ (2 mM), totally inhibited by harmaline (10(-4) M) and only partially inhibited by ouabain (10(-2) M). Potassium content rises rapidly after fertilization by an undefined mechanism and is further increased via the Na+/K+ exchange. The Na+/Ka+ exchange increases the cytoplasmic K+/Na+ ratio of the egg from 6 to 12 in the first hour after fertilization. When fertilization occurs in low K+ SW, where the Na+/K+ exchange is reduced, the ratio Na+/K+ decreases and the embryos develop with a preponderance of ectodermal structures (animalization).

Animals↗
PubMed1980

Changes in permeability of sea urchin egg membrane to urea after fertilization or activation.

1. Fertilization or artificial activation of the sea urchin egg, are known to increase the plasma membrane permeability to ions and small metabolites. We have examined the permeability properties of the egg membrane to urea. 2. Urea influx is not saturable and is slightly dependent on temperature. It is inhibited by phloretin. 3. Fertilization leads to a biphasic increase in urea flux kinetics. The first acceleration lasts about 10 min. The second acceleration is maintained at least up to the first cleavage. 4. The ionophore A 23187 mimics exactly fertilization. 5. Weak bases such as procaine lead to a gradual acceleration in urea flux kinetics. The response depends on the dose of procaine added. 6. The inhibitor of oxydative phosphorylation 2,4-DNP fails to block the accelerations triggered by fertilization or activation by A 23187. 7. We discuss the results in light of the early and late events of egg activation.

Animals↗
PubMed1980

Freeze fracture of the gill epithelium of euryhaline teleost fish.

We briefly discuss the information one can obtain using freeze fracture. We used this technique to precisely identify the types of junctions that link the cells of the gill epithelium of euryhaline teleosts. In particular we demonstrate that seawater adaptation is characterized by the appearance of new apical tight junctions between chloride cells. Another particularity of these cells, the extensive network of tubules, extension of the basolateral plasma membrane, is shown to be made of repetitive units. We discuss the functional importance of the observations with respect to the adaptation of fish to different salinities.

Animals↗
PubMed1980

Polysaccharidic material in chloride cell of teleostean gill: modifications according to salinity.

The gill epithelium is known to be implicated in the hydromineral regulation of teleosts, especially owing to its "chloride cells." We have examined the polysaccharides of chloride cells from euryhaline teleosts adapted to fresh- or saltwater. The use of periodic acid-chromic acid-silver methenamine, colloidal thorium, or radioautography after incorporation of [3H]glucosamine has shown that chloride cells are characterized by a high concentration of polysaccharides in their apical region (at the level of the vesiculotubular system) and by a special polysaccharidic cell coat. The polysaccharide molecules originate from the Golgi area; by 12 h they accumulate within the vesiculotubular system and are released in the apical cavity of the cell within 24 h. In fresh- and saltwater-adapted fish, the localization of polysaccharidic material in chloride cells is basically the same. However, in saltwater-adapted fish, the amount and turnover of the polysaccharide molecules are clearly increased.

Adaptation, Physiological↗