排序方式: 共有34条查询结果,搜索用时 343 毫秒
1.
Ouabain-insensitive salt and water movements in duck red cells. II. Norepinephrine stimulation of sodium plus potassium cotransport 总被引:11,自引:9,他引:2
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Catecholamines induce net salt and water movements in duck red cells incubated in isotonic solutions. The rate of this response is approximately three times greater than a comparable effect observed in 400 mosmol hypertonic solutions in the absence of hormone (W.F. Schmidt and T. J. McManus. 1977 a.J. Gen. Physiol. 70:59-79. Otherwise, these two systems share a great many similarities. In both cases, net water and salt movements have a marked dependence on external cation concentrations, are sensitive to furosemide and insensitive to ouabain, and allow the substitution of rubidium for external potassium. In the presence of ouabain, but the absence of external potassium (or rubidium), a furosemide-sensitive net extrusion of sodium against a large electrochemical gradient can be demonstrated. When norepinephrine-treated cells are incubated with ouabain and sufficient external sodium, the furosemide-sensitive, unidirectional influxes of both sodium and rubidium are half- maximally saturated at similar rubidium concentrations; with saturating external rubidium, the same fluxes are half-maximal at comparable levels of external sodium. In the absence of sodium, a catecholamine-stimulated, furosemide-sensitive influx of rubidium persists. In the absence of rubidium, a similar but smaller component of sodium influx can be seen. We interpret these results in terms of a cotransport model for sodium plus potassium which is activated by hypertonicity or norepinephrine. When either ion is absent from the incubation medium, the system promotes an exchange-diffusion type of movement of the co-ion into the cells. In the absence of external potassium, net movement of potassium out of the cell leads to a coupled extrusion of sodium against its electrochemical gradient. 相似文献
2.
3.
4.
Both Trichodorus spp. and Longidorus spp. damage roots of sugar-beet seedlings in sandy soil, causing Docking disorder. Trials in infested fields between 1969 and 1972 tested the effects of fumigation along the rows with different amounts of D-D or Telone applied either two weeks before sowing or immediately before sowing, application of the systemic nematicide aldicarb (Temik) in the furrow with the seed during sowing, and top-dressing with nitrogen. Seedling establishment was often decreased by fumigation immediately before sowing, especially when followed by excessive rainfall, but only rarely by earlier fumigation or by aldicarb; differences in numbers of roots harvested were smaller because hand-singling removed excess seedlings. There was usually little difference between the yield increases given by the most effective treatments, which were aldicarb at 1·12 kg active ingredient/ha and 2·2–6·6 ml D-D or Telone/m of row at either time of application. Nitrogen top-dressing never affected sugar yield significantly. Longidorus spp. and Trichodorus spp. were both controlled well in the fumigated row but much less well at 13 cm, and not at all at 25 cm from the row (i.e. mid-way between two treated rows). 相似文献
5.
The effects of completely defoliating sugar beet at different dates from May to October were examined in four years. In each year there were plots given the usual nitrogen fertiliser application to the seedbed, and also in two of the years plots given no nitrogen. At harvest in mid-November, minimum root weights followed defoliation in July or August, but defoliation in August or later gave minimum sugar contents. When nitrogen was applied to the seedbed sugar yields were smallest after August defoliation; in the absence of nitrogen, July defoliation gave the lowest sugar yields, root yield being smaller but sugar content usually greater than with nitrogen. Up to 40% of the sugar yield was lost by July or August defoliation and late defoliation increased some of the impurities in the root juice. Yields, and recovery from defoliation, were greater with nitrogen than without. Partial defoliation in May had relatively little effect on yield. Defoliation affected the incidence of virus yellows differently in different years. 相似文献
6.
Restriction-map variation associated with the G6PD polymorphism in natural populations of Drosophila melanogaster 总被引:10,自引:0,他引:10
Restriction-map variation was studied in 126 copies of the G6pd region in X
chromosome lines of Drosophila melanogaster from North America, Europe, and
Africa. Special attention was focused on the distribution of variation
relative to the geographically variable polymorphism for two
electrophoretic variants. Nucleotide heterozygosity as determined by eight
six-cutter restriction enzymes for the 13-kb region is estimated, on the
basis of the worldwide sample, to be 0.065%, which is the lowest value
reported for any comparable region in the D. melanogaster genome.
Significant linkage disequilibrium between electrophoretic alleles and
restriction-site variation is observed for several sites. In contrast to
published studies of other genetic regions, there are large insertions that
reach significant frequencies and are found across considerable geographic
distances. There is a clustering of this variation inside the first large
intervening sequence of the G6PD gene.
相似文献
7.
8.
9.
Sander A Huisman Wendy Bijman-Lagcher Jan NM IJzermans Ron Smits Ron WF de Bruin 《Cell cycle (Georgetown, Tex.)》2015,14(14):2333-2339
Irinotecan is a widely used topoisomerase-I-inhibitor with a very narrow therapeutic window because of its severe toxicity. In the current study we have examined the effects of fasting prior to irinotecan treatment on toxicity and anti-tumor activity. FabplCre;Apc15lox/+ mice, which spontaneously develop intestinal tumors, of 27 weeks of age were randomized into 3-day fasted and ad libitum fed groups, followed by treatment with a flat-fixed high dose of irinotecan or vehicle. Side-effects were recorded until 11 days after the start of the experiment. Tumor size, and markers for cell-cycle activity, proliferation, angiogenesis, and senescence were measured. Fasted mice were protected against the side-effects of irinotecan treatment. Ad libitum fed mice developed visible signs of discomfort including weight loss, lower activity, ruffled coat, hunched-back posture, diarrhea, and leukopenia. Irinotecan reduced tumor size in fasted and ad libitum fed groups similarly compared to untreated controls (2.4 ± 0.67 mm and 2.4 ± 0.82 mm versus 3.0 ± 1.05 mm and 2.8 ± 1.08 mm respectively, P < 0.001). Immunohistochemical analysis showed reduced proliferation, a reduced number of vascular endothelial cells, and increased levels of senescence in tumors of both irinotecan treated groups. In conclusion, 3 days of fasting protects against the toxic side-effects of irinotecan in a clinically relevant mouse model of spontaneously developing colorectal cancer without affecting its anti-tumor activity. These results support fasting as a powerful way to improve treatment of colorectal carcinoma patients. 相似文献
10.
Nucleotide variation in the triosephosphate isomerase (Tpi) locus of Drosophila melanogaster and Drosophila simulans 总被引:3,自引:0,他引:3
Hasson E; Wang IN; Zeng LW; Kreitman M; Eanes WF 《Molecular biology and evolution》1998,15(6):756-769
DNA sequence variation in a 1.1-kb region including the coding portion of
the Tpi locus was examined in 25 homozygous third-chromosome lines of
Drosophila melanogaster, nine lines of Drosophila simulans, and one line of
Drosophila yakuba. Our data show that the widespread allozyme polymorphism
observed in cosmopolitan D. melanogaster is due to a glutamic acid
substitution occurring in a phylogenetically conserved lysine that has been
identified as part of the "hinged-lid" active site of the enzyme. This
observation suggests that the replacement polymorphism may have important
functional consequences. One replacement polymorphism was also observed in
D. simulans, although its functional relevance is more difficult to assess,
since it affects a site that is not strongly conserved. This amino acid
change in D. simulans is associated with a single lineage possessing seven
unique silent substitutions, which may be indicative of balancing selection
or population subdivision. The absence of fixed amino acid differences
between D. melanogaster and D. simulans and only a single difference with
D. yakuba suggests that triose phosphate isomerase is under strong
functional constraint. Silent variation is slightly higher for D.
melanogaster than for D. simulans. Finally, we outline the general lack of
evidence for old balanced polymorphisms at allozyme loci in D.
melanogaster.
相似文献