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S D Levine M Jacoby 《Biology of the cell / under the auspices of the European Cell Biology Organization》1989,66(1-2):23-27
Although it is well accepted that vasopressin (ADH) increases the permeability to water of the toad bladder granular cell's luminal membrane, recent studies have suggested that regulation also takes place at an additional "postluminal" site within the epithelial granular cell. These studies are based upon the observation that a number of experimental maneuvers can alter tissue permeability to water, but do not change the number of particle aggregates observed on the protoplasmic face of the granular cell's luminal membrane with freeze-fracture electron microscopy. These aggregates are believed by many investigators to mediate the transport of water across the luminal membrane. The dissociation between permeability and aggregate frequency described above has been variously interpreted as the consequence of changes in the permeability of the aggregates themselves, or of changes in the permeability of a "postluminal" barrier that is functionally in series with the luminal membrane. We attempted to distinguish between these 2 possibilities by studying paired toad bladders during 3 protocols that alter vasopressin-stimulated water flow across the intact tissue without altering aggregate frequency. Estimates of the permeability of postluminal barriers were obtained by exposing the luminal surface to amphotericin B, an antibiotic that forms water-permeant channels in the luminal membrane. Of the 3 protocols, only diminishing bladder filling volume decreased the water flow elicited by luminal amphotericin B, suggesting that only that protocol indeed decreased the permeability of some postluminal barrier. The other 2 protocols, increasing PCO2 and repeatedly stimulating the bladder with vasopressin, did not alter amphotericin B-elicited flow, suggesting that postluminal barriers were not altered by these 2 protocols.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Ohne Zusammenfassung 相似文献
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The water permeability of toad urinary bladder. II. The value of Pf/Pd(w) for the antidiuretic hormone-induced water permeation pathway 总被引:4,自引:1,他引:3 下载免费PDF全文
Using the methods described in the preceding paper (Levine et al., 1984) for measuring the magnitude of the water-permeable barriers in series with the luminal membrane, we correct measured values of Pd(w) in bladders stimulated with low doses of antidiuretic hormone (ADH) or 8-bromo cyclic AMP to obtain their true values in the luminal membrane. Simultaneously, we also determine Pf. We thus are able to calculate Pf/Pd(w) for the hormone-induced water permeation pathway in the luminal membrane. Our finding is that Pf/Pd(w) approximately equal to 17. Two channel models consistent both with this value and the impermeability of the ADH-induced water permeation pathway to small nonelectrolytes are: (a) a long (approximately equal to 50 A), small- radius (approximately equal to 2 A) pore through which 17 water molecules pass in single-file array, and (b) a shower-head-like structure in which the stem is long and of large radius (approximately equal to 20 A) and the cap has numerous short, small-radius (approximately equal to 2 A) pores. A third possibility is that whereas the selective permeability to H2O results from small-radius (approximately equal to 2 A) pores, the large value of Pf/Pd(w) arises from their location in the walls of long tubular vesicles (approximately 2 micron in length and 0.1 micron in diameter) that are functionally part of the luminal membrane after having fused with it. Aggregate-containing tubular vesicles of these dimensions have been reported to fuse with the luminal membrane in response to ADH stimulation and have been implicated in the ADH-induced hydroosmotic response. 相似文献
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Delineation of suppressor and helper activity within the OKT4-defined T lymphocyte subset in human newborns 总被引:6,自引:0,他引:6
Lymphocytes taken from the cord blood of newborns have active suppressor activity. Using in vitro PWM-stimulated cocultures, unfractionated T cells from newborns potently suppressed the expected immunoglobulin G (IgG) synthesis of their mothers' peripheral blood lymphocytes (PBL). Using positive and negative selection techniques, we characterized the active suppressor cell as expressing the OKT4+T8- phenotype. This cord blood lymphocyte subset suppressed maternal IgG synthesis after depletion of maternal suppressor cells, implicating the ability of newborn T cells to suppress directly rather than by inducing adult suppressor activity. Sublethal amounts (1500 rad) of gamma-irradiation fully abrogated the suppressor activity of cord blood T lymphocytes. Radioresistant cord T cells provided T cell help. Irradiation of cord OKT4+ and OKT8+ populations and their subsequent culture with maternal B cells determined that helper activity was a radioresistant subpopulation of the OKT4+ subset. These results indicate significant differences in the functional properties of T cell subsets from adults and newborns. Population studies determined that cord blood lymphocytes had a greater proportion of OKT4+ cells and lower proportion of OKT8+ cells than PBL from unrelated adults. The mothers tested had similar proportions of OKT4+ cells as their babies, and these levels are significantly higher than those of unrelated adults. 相似文献
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L B Jacoby 《Experimental cell research》1974,84(1):167-174
DNA synthesis is initiated in unfertilized sea urchin eggs (Strongylocentrotus purpuratus and Lytechinus pictus) by exposing them to NH4OH-sea water (ordinary sea water titrated to pH 9–9.1 with NH4OH). The eggs are considered to be unfertilized eggs by visual and electro-biological criteria and because they can later be fertilized and then do give visible and electrobiological fertilization reactions. The incorporation of 3H-thymidine proceeds in rounds, the magnitude increasing in successive rounds. It is also reported that the treatment with NH4OH activates the uptake of thymidine by the eggs, although the internal thymidine builds up more slowly in unfertilized eggs treated with NH4OH than it does in fertilized eggs. The magnitude of the incorporation of exogenously supplied labelled thymidine into DNA is lower in the NH4OH-treated unfertilized eggs than in normal fertilized eggs. This difference is not attributed to differences in the amount of DNA synthesized and the explanation is sought in thymidine uptake and nucleotide pathways. 相似文献
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Transferable plasmids in gram-negative bacteria that confer resistance to potassium tellurite or tellurate were found. This re-istance was distinct from resistance to mercury, silver, or arsenic compounds and was unrelated to antibiotic resistance. In Escherichia coli, plasmids determine a 100-fold increase in the minimal inhibitory concentration for tellurite and a 10-fold increase in tellurate resistance. Many, but not all, of the plasmids belong to incompatibility group S. In Pseudomonas aeruginosa, tellurium resistance is specifically associated with incompatibility group P-2 and involves a 5- to 10-fold increase in tellurite or tellurate resistance. 相似文献
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Several commonly used serotonin receptor antagonists were studied for their ability to influence basal plasma insulin and glucagon (using 30K antibody) levels as well as the response of these hormones to a glucose or arginine challenge administered systematically to overnight fasted rats. Cyproheptadine, in contrast to other antagonists employed, induced large increases of insulin, glucagon and glucose, although this hyperinsulinemia was of a smaller magnitude when compared with hormone levels observed during an equivalent hyperglycemia resulting from glucose administration. The pancreatic response to a glucose load (increased insulin and decreased glucagon release) and an arginine load (increased insulin and glucagon release) were prevented by cyproheptadine pretreatment. Basal insulin levels were bot consistently altered by methysergide or cinanserin and were slightly elevated by metergoline. Basal glucagon levels were unaffected by these drugs. These three agents potentiated the insulinotropic effect of an arginine load whereas only metergoline exerted a similar effect on the response to glucose loading. Glucagon release in response to these stimuli was not significantly altered by drug pretreatment. 相似文献