Showing papers on "Toad published in 1977"

Acetylcholine receptors in the oocyte membrane.

Abstract: IN vertebrates, fully differentiated cells such as skeletal muscle and some nerve cells are highly sensitive to acetyl-choline (ACh), due to the presence of acetylcholine receptors in their surface membranes. In muscle fibres, the ACh-sensitivity is known to appear early during differentiation1–3, but relatively little is known about the chemical sensitivity of the membrane in the undifferentiated cell. In particular, it would be interesting to know if spermatozoa and oocytes are already sensitive to ACh and other neurotransmitter substances. To examine this question, toad (Xenopus laevis) oocytes were taken from the ovary, kept in frog's Ringer or Merriam4 solution, and studied at room temperature, using conventional electrophysiological techniques.

Relationship of aggregated intramembranous particles to water permeability in vasopressin-treated toad urinary bladder.

Abstract: It has been previously demonstrated with freeze-fracture electron microscopy that vasopressin induces specific structural alterations of the luminal membrane of granular cells from toad urinary bladder in a dose-dependent fashion. These alterations consist of aggregated intramembranous particles and are observed both in the presence and absence of an osmotic gradient. We examined the effect of methohexital, a selective inhibitor of vasopressin-stimulated water flow, and the effect of phloretin, a selective inhibitor of urea permeability, on the structure of the granular cell luminal membrane. Methohexital treatment of the vasopressin-stimulated toad bladder reduced both the osmotic water flow and vasopressin-induced alterations of membrane structure to the same extent. Phloretin reduced urea permeability but not water flow or particle aggregation. Since neither agent affects vasopressin-stimulated sodium movement, these findings indicate that the phenomenon of particle aggregation is specifically related to vasopressin-induced water permeability and not to changes in urea or sodium permeability.

Particle aggregates in plasma and intracellular membranes of toad bladder (granular cell).

Abstract: Freeze-fracture of granular cells of toad urinary bladder (Bufo marinus) reveals the presence, hitherto undescribed, of intramembranous particle aggregates in intracytoplasmic structures (tubules, vacuoles and vesicles) both in resting and vasopressin-stimulated epithelia.

Inhibition of vasopressin-stimulated prostaglandin E biosynthesis by chlorpropamide in the toad urinary bladder. Mechanism of enhancement of vasopressin-stimulated water flow.

Abstract: Chlorpropamide is known to enhance the water permeability response of the toad urinary bladder to vasopressin and to theophylline In other studies, we have shown that prostaglandin E synthesis by the toad bladder inhibits the water permeability response to arginine vasopressin and to theophylline In this study, the effect of chlorpropamide on vasopressin-, theophylline-, and cyclic AMP-stimulated water flow and on prostaglandin E biosynthesis was investigated in the toad urinary bladder in vitro Chlorpropamide inhibited prostaglandin E biosynthesis during vasopressin-, theophylline- and cyclic AMP-stimulated water flow Tolbutamide and glyburide, two other sulfonylurea compounds, also enhanced vasopressin-stimulated water flow and inhibited vasopressin-stimulated prostaglandin E biosynthesis We conclude that the mechanism of enhancement on vasopressin-stimulated water flow by the sulfonylureas is the inhibition of prostaglandin E biosynthesis

Acyl groups, molecular species, and labeling by 14C-glycerol and 3H-arachidonic acid of vertebrate retina glycerolipids.

Abstract: The toad retina diacylglycerol content is high and enriched in docosahexaenoate, both in comparison with toad brain and mammalian retina (Aveldano & Bazan, 1973, 1974) as well as with mammalian brain diacylglycerols (Sun, 1970; Keough et al., 1972; Aveldano & Bazan, 1975) where arachidonic acid predominates. This suggested that diacylglycerols in the toad retina may be uniquely engaged in the metabolism of 22:6-containing membrane lipids. Here we report an analysis of acyl groups and molecular species showing further peculiarities in toad retina lipids. In addition the cattle and toad retina glycerolipid labeling by 14C-glycerol and 3H-arachidonic acid is surveyed.

Effects of neurotransmitters upon the discharge of secretory product from the cutaneous glands of the red-spotted newt.

Abstract: The effects of sympathetic and parasympathetic agonists and antagonists on discharge of secretory product by the granular and mucous glands were examined in the red-spotted newt, Notopthalmus viridescens viridescens. Observations were made also on the South African clawed toad, Xenopus laevis, the grass frog, Rana pipiens, and the crested newt, Triturus cristatus. In contrast to the granular glands of the South African clawed toad and the grass frog, which were stimulated by α-adrenergic agents, those of the red-spotted newt discharge in response to acetylcholine, either in vitro when added to the Holtfreter's solution in which explants were incubated, or in vivo when injected subcutaneously. Granular glands of the crested newt were also discharged in response to subcutaneous injection of acetylcholine. Stimulation of the granular glands by acetylcholine was blocked by atopine but not by tubocurarie, indicating that the cholinergic receptors are muscarinic rather than nicotinic. The mucous glands of the red-spotted newt, on the other hand, did not discharge in response to either acetylcholine or to adrenergic agents.

Some ultrastructural observations on the intestinal mucosa of the toad (Bufo melanostictus).

Abstract: An ultrastructural study of the mucous membrane of the small intestine in the toal (Bufo melanostictus) has shown that in the epithelium, besides the typical epithelial lining cells, non-epithelial cell types, including lymphocytes, macrophases, plasma cells, eosinophils and neutrophils are present These non-epithelial cell types are also encountered in the lamina propria, which also contains numerous fibroblasts, smooth muscle cells and mast cells The ultrastructural features of toad intestinal mucous membrane thus resembles that in mamals in many of its features, The intraepithelial localization of macrophages and of mature plasma cells is unusual The observations suggest that the toad intestinal mucous membrane may function as a lymphoepithelial organ

Lipid metabolism in early development using labeled precursors incorporated during oogenesis and in cell-free embryo homogenates.

Abstract: Embryos of the toad,Bufo arenarum, Hensel, taken during early stages of development were used to survey the [U-14C] glycerol and32P lipid labeling. When precursors were supplied at the time of oogenesis, large differences in specific activities of phospholipid were observed. Using32P, a steep rise as a function of development was evidenced. Triglycerides contained much higher proportions of [U-14C] glycerol than phospholipids when administered to the female toad along with a pituitary homogenate. However, lack of [U-14C] glycerol uptake into lipids was observed when cell-free homogenates of eggs at different stages of development ranging from unfertilized oocyte to midgastrula were incubated in unsupplemented amphibian Ringer. At the later stage, significant de novo biosynthesis of lipids from glycerol began to be measurable, whereas during cell cleavage intracellular redistribution of preformed phosphoglycerides was used for membrane assembly.

Testicular Leydig cells and 277-1277-1277-1dehydrogenase in cadmium-treated toads (Bufo melanostictus)

Abstract: Injection of cadmium chloride in toad increased Leydig cell size (area) and Δ5-3β-hydroxysteroid dehydrogenase activity in the testis.

3H-fucose incorporation into glycoproteins of toad bladder epithelial cells.

Abstract: Electron microscope autoradiography was used to detect the incorporation of 3H-fucose into glycoproteins of toad bladder epithelial cells. After short exposure to 3H-fucose, without a chase period, the Golgi regions of all four cell types were labeled. When exposure to 3H-fucose was followed by chase periods (1,3,4 and 6 hours) the apical and basal-lateral plasma membranes of granular cells were heavily labeled. Apical granules and the cytoplasm of granular cells were also labeled, suggesting that they both provide the means for glycoprotein transfer from the Golgi to the plasma membranes. The heaviest labeling in mitochondria-rich cells, after the 1- and 3-hour chase periods, was over the apical tubules, although the apical and basal-lateral plasma membranes were also heavily labeled. After 4- and 6-hour chases, the labeling of the apical tubules decreased, whereas the labeling of the plasma membranes increased, strongly suggesting that in these cells apical tubules play a major role in the transfer of glycoproteins from the Golgi to the plasma membrane. Our results demonstrate that the route of 3H-fucose incorporation into plasma membrane glycoproteins and the rate of glycoprotein synthesis and breakdown are not the same in the two major epithelial cell types in toad bladder.

Action of vasopressin, ouabain, and cyanide on the volume of isolated toad bladder epithelial cells.

Abstract: Toad bladder epithelial cells were isolated under mild conditions in a calcium-free medium; they were found to exclude trypan blue, to consume oxygen, and to respond to vasopressin with an increased rate of oxygen consumption. Since isolated toad bladder epithelial cells are mostly spherical in shape, the cell diameter can be accurately measured with an ocular micrometer of an inverted microscope. Epithelial cells swelled by 29±3% in the presence of KCN. This cyanide-induced swelling of cells was prevented by amiloride or, alternatively, by replacing NaCl by equiosmotic amounts of mannitol in the Ringer's fluid. Cells incubated in the presence of vasopressin swelled by 10±2%. Vasopressin and KCN acted synergistically in enhancing cell volume. Ouabain caused cells to swell by 9±2%, and this effect was not additive to the swelling seen with vasopressin. These observations are in accord with the theory of Leaf and his associates, that the predominant effect of vasopressin is to enhance sodium entry into the transporting epithelial cells of the toad urinary bladder.

Active phosphate transport across the urinary bladder of the toad,Bufo marinus

Abstract: Net transport of inorganic phosphate occurs in the absence of an electrochemical gradient from the mucosal to the serosal bathing solution in the isolated toad urinary bladder. This transport can be inhibited by metabolic inhibitors. The magnitude of this transport can be altered by changes in phosphate concentration or by the addition of parathyroid hormone.

Histochemistry of the juxtaglomerular apparatus in the toad Bufo bufo. The glucose-6-phosphate dehydrogenase activity of the macula densa.

Abstract: An investigation regarding the question of whether there exists a macula densa as part of the juxtaglomerular apparatus in the kidney of amphibians has been carried out. With the aid of a histochemical reaction for glucose-6-phosphate dehydrogenase activity, the presence of a macula densa zone as a specialized part of the distal tubule in the toad Bufo bufo was demonstrated. The functional significance of the high glucose-6-phosphate dehydrogenase activity in the macula densa cells is discussed.

Difference between frog and toad tadpoles in response of the keratinizing epidermis of the oral region to excess of vitamin A

Abstract: Rearing of the tadpoles of the frog,Rana breviceps, in solutions containing 2.5, 5, 7.5, 10 and 15 IU/ml vitamin A palmitate resulted in reduction or complete disappearance of the keratinized epidermal material over the jaws and of the horny labial teeth. The tadpoles of the toad,Bufo andersonii, however, were not affected in this way at all by exposure to even 20 and 30 IU/ml vitamin A in the rearing medium.

A comparison of the uptake of [1-14C]palmitate into cell fractions of the perfused toad, chick and guinea-pig heart.

Abstract: 1. 1. The incorporation and washout of [1-14C]palmitate in the subcellular fractions of toad, chick and guinea-pig hearts has been studied at warm and cold temperatures. 2. 2. Maximal FFA radioactivity generally occurred in the microsomal fraction. Washout of radioactivity in chick and guinea-pig hearts virtually ceased in the cold, while in the toad it was only moderately affected. 3. 3. The microsomal esterification process was temperature dependent. It was most active in the guinea-pig and least active in the toad.