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51.
Stimulant-evoked depolarization and increase in [Ca2+]
i
in insulin-secreting cells is dependent on external Na+ 总被引:1,自引:0,他引:1
M. J. Dunne D. I. Yule D. V. Gallacher O. H. Petersen 《The Journal of membrane biology》1990,113(2):131-138
Summary The patch-clamp technique and measurements of single cell [Ca2+]
i
have been used to investigate the importance of extracellular Na+ for carbohydrate-induced stimulation of RINm5F insulin-secreting cells. Using patch-clamp whole-cell (current-clamp) recordings the average cellular transmembrane potential was estimated to be –60±1 mV (n=83) and the average basal [Ca2+]
i
102±6nm (n=37). When challenged with either glucose (2.5–10mm) ord-glyceraldehyde (10mm) the cells depolarized, which led to the initiation of Ca2+ spike potentials and a sharp rise in [Ca2+]
i
. Similar effects were also observed with the sulphonylurea compound tolbutamide (0.01–0.1mm). Both the generation of the spike potentials and the increase in [Ca2+]
i
were abolished when Ca2+ was removed from the bathing media. When all external Na+ was replaced with N-methyl-d-glucamine, in the continued presence of either glucose,d-glyceraldehyde or tolbutamide, a membrane repolarization resulted, which terminated Ca2+ spike potentials and attenuated the rise in [Ca2+]
i
. Tetrodotoxin (TTX) (1–2 m) was also found to both repolarize the membrane and abolish secretagogue-induced rises in [Ca2+]
i
. 相似文献
52.
Keila?Cristina?Novais?Porto Yule?Roberta?Ferreira?Nunes Leonardo?Monteiro?RibeiroEmail author 《Plant Ecology》2018,219(2):199-207
The Mauritia flexuosa palm tree is widely distributed in South America, and is associated with flooded environments. It dominates the arboreal stratum in the highly threatened marsh ecosystems called “veredas” in the Cerrado biome (neotropical savanna), and its oleaginous fruits are important for the maintenance of the regional fauna and as a source of income for traditional human populations. The seeds of this palm demonstrate an unusual association of recalcitrance and dormancy, and information about its seed bank maintenance in natural environments is scarce. We measured the variations in water content, viability, and germination of seeds maintained over 1 year in four typical vereda microenvironments (edge, near the water, in the water, and at the lower zone of the vereda) and related that information to soil water contents and climatic data. Seed viability was best preserved under constantly flooded conditions (at the lower zone of the vereda), with the potential for maintaining a temporary seed bank in the aquatic environment that would favor dispersal. Although the seeds are intolerant of dehydration, they have a high capacity for maintaining their water contents under partially drained soil conditions, and overcoming dormancy is favored under those conditions. Mauritia flexuosa establishment strategies are driven by sophisticated interactions with climate and with vereda microenvironments, with a tendency for maintaining seed banks and seedling banks in localities with flooded or drained soils, respectively. 相似文献
53.
Compensatory substitutions and the evolution of the mitochondrial 12S rRNA gene in mammals 总被引:5,自引:2,他引:3
12S ribosomal RNA (rRNA) gene sequences from a suite of mammalian taxa (13
placentals, 4 marsupials, 1 monotreme), for which phylogenetic
relationships are well established based on independent criteria, were
employed to study the evolution of this gene. Phylogenetic analysis of 12S
sequences produces a phylogeny that agrees with expectations. Base
composition provides evidence for directional symmetrical substitution
pressure in loops; in stems, base composition is much more even. Rates of
nucleotide substitution are lower in stems than loops. Patterns of
nucleotide substitution show an overall preference for transitions over
transversions, with this difference more profound in stems than loops.
Among different transversion pathways, there is a wide range of
transformation frequencies. An analysis of compensatory substitutions shows
that there is strong evidence for their occurrence and that a weighting
factor of 0.61 should be applied in phylogenetic analyses to account for
the dependence of mutations at stem positions relative to positions where
changes are independent. Among stem variables (i.e., stem length,
interaction distance, substitution rates, G+C content, and the percentage
of bases that are paired), several significant correlations were
discovered, but stem length and interaction distance are uncorrelated with
other variables.
相似文献
54.
The pedunculated cirripedePollicipes pollicipes is of considerable economic importance in Portugal, particularly along the southwest coast. Current knowledge of its biology is poor, as evidenced by the paucity of available literature. This paper reports on the reproduction of twoP. pollicipes populations, Castelejo and Zavial, on the southwest coast of the Algarve. Differences in reproductive patterns between the two sites were minor and not statistically significant, despite differences in environmental conditions between the two sites. Adult animals carried fertilised eggs from April throughout September, and the percentage of individuals with egg masses correlated positively with air but not with sea water temperature. Brooding success was greater with average air temperature in excess of 14°C during months of strong upwelling and presumed food availability. Functional ovaries and testes are available in the population all year round but fertilisation does not appear to occur during the winter months. Reproduction ofP. pollicipes on the southwest coast of the Algarve appears closely linked to the upwelling phenomenon with the rate of deposition of gonadal tissue probably being determined by environmental temperature. The cues which determine the cessation of fertilisation remain to be investigated. 相似文献
55.
为了探讨特定电磁波(TDP)对精子超弱化学发光和体外获能的影响,本文用不同剂量的TDP辐照处理家兔精液,对精子超弱化学发光及体外获能进行了研究.实验结果表明,适宜剂量TDP辐照家兔精液,可使其超弱化学发光增强,并对精子体外获能和顶体与反应有诱导和促进作用,大剂量的TDP辐照有促进获能精子死亡的作用.经过对精子超弱化学发光和精子直顶体反应率的相关分析,结果表明,二者呈强正相关(r=0.805,P<0.01). 相似文献
56.
Distribution of histopathology and Ia positive cells in actively induced and passively transferred experimental autoimmune orchitis 总被引:4,自引:0,他引:4
K S Tung T D Yule C A Mahi-Brown M B Listrom 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(3):752-759
Histopathology in testes from mice with actively induced experimental orchitis (EAO) (active EAO) and those from recipients of testis-sensitized lymphocytes (passive EAO) had different distributions. In passive EAO, maximum orchitis existed in the straight tubules, rete testis, and ductus efferentes, obstruction of which led to extreme dilatation of seminiferous tubules. Unusual intralymphatic granulomata also resulted in dilated testicular lymphatics. In active EAO, maximum orchitis affected seminiferous tubules under the testicular capsule, away from the rete testes. Vasitis was common and occurred in both active and passive EAO. In normal testes, IA+ F4/80+ cells were sparse but formed a cuff around the straight tubules. After immunization with testis in adjuvant or with adjuvant alone, the number, size, and staining intensity of IA+ cells increased dramatically beginning on day 5, 7 days before disease onset. Simultaneously, epithelial cells confined to the ductus efferentes became Ia+. Although recipients of sensitized lymphocytes also developed epithelial Ia in the ductus efferentes, they did not show changes in testicular interstitial Ia+ cells. Our findings indicate that testicular autoantigens are not completely sequestered, but are accessible to and can react with passively transferred immune lymphocytes in well-defined regions of the germ cell compartment. These regions coincided to a large extent with maximum expression of periductal or epithelial Ia. Changes in Ia+ cells in the testis, which are inducible by adjuvants and precede orchitis, may account in part for the different distribution of histopathology of active EAO. 相似文献
57.
Accumulation of glucosinolates, a class of defense-related secondary metabolites found almost exclusively in the Capparales, is induced in response to a variety of biological stresses. It is often assumed that elevated glucosinolate levels result from de novo biosynthesis, but glucosinolate transport from other parts of the plant to the site of herbivory or pathogen infection can also contribute to the defense response. Several studies with Arabidopsis and other crucifers have demonstrated that glucosinolates from vegetative tissue are transported to developing seeds. Here we discuss evidence that long-chain aliphatic glucosinolates are transported to the site of herbivory in response to Myzus persicae (green peach aphid) feeding on Arabidopsis.Key Words: glucosinolate, transport, graft, Arabidopsis, Myzus persicae, aphid 相似文献
58.
59.
Dejong JM Liu Y Bollon AP Long RM Jennewein S Williams D Croteau RB 《Biotechnology and bioengineering》2006,93(2):212-224
Baccatin III, an intermediate of Taxol biosynthesis and a useful precursor for semisynthesis of the anti-cancer drug, is produced in yew (Taxus) species by a sequence of 15 enzymatic steps from primary metabolism. Ten genes encoding enzymes of this extended pathway have been described, thereby permitting a preliminary attempt to reconstruct early steps of taxane diterpenoid (taxoid) metabolism in Saccharomyces cerevisiae as a microbial production host. Eight of these taxoid biosynthetic genes were functionally expressed in yeast from episomal vectors containing one or more gene cassettes incorporating various epitope tags to permit protein surveillance and differentiation of those pathway enzymes of similar size. All eight recombinant proteins were readily detected by immunoblotting using specific monoclonal antibodies and each expressed protein was determined to be functional by in vitro enzyme assay, although activity levels differed considerably between enzyme types. Using three plasmids carrying different promoters and selection markers, genes encoding five sequential pathway steps leading from primary isoprenoid metabolism to the intermediate taxadien-5alpha- acetoxy-10beta-ol were installed in a single yeast host. Metabolite analysis showed that yeast isoprenoid precursors could be utilized in the reconstituted pathway because products accumulated from the first two engineered pathway steps (leading to the committed intermediate taxadiene); however, a pathway restriction was encountered at the first cytochrome P450 hydroxylation step. The means of overcoming this limitation are described in the context of further development of this novel approach for production of Taxol precursors and related taxoids in yeast. 相似文献
60.
Mario PL Calus Theo HE Meuwissen Jack J Windig Egbert F Knol Chris Schrooten Addie LJ Vereijken Roel F Veerkamp 《遗传、选种与进化》2009,41(1):11
The aim of this paper was to compare the effect of haplotype definition on the precision of QTL-mapping and on the accuracy of predicted genomic breeding values. In a multiple QTL model using identity-by-descent (IBD) probabilities between haplotypes, various haplotype definitions were tested i.e. including 2, 6, 12 or 20 marker alleles and clustering base haplotypes related with an IBD probability of > 0.55, 0.75 or 0.95. Simulated data contained 1100 animals with known genotypes and phenotypes and 1000 animals with known genotypes and unknown phenotypes. Genomes comprising 3 Morgan were simulated and contained 74 polymorphic QTL and 383 polymorphic SNP markers with an average r2 value of 0.14 between adjacent markers. The total number of haplotypes decreased up to 50% when the window size was increased from two to 20 markers and decreased by at least 50% when haplotypes related with an IBD probability of > 0.55 instead of > 0.95 were clustered. An intermediate window size led to more precise QTL mapping. Window size and clustering had a limited effect on the accuracy of predicted total breeding values, ranging from 0.79 to 0.81. Our conclusion is that different optimal window sizes should be used in QTL-mapping versus genome-wide breeding value prediction. 相似文献