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211.
212.
The role of Ca2+ in the human sperm acrosome reaction was investigated using the fluorescent calcium indicator fura-2. Previous experiments have shown that a Sephadex G-75 column fraction of human follicular fluid can stimulate the human sperm acrosome reaction [Suarez SS, Wolf DP, Meizel S (1986): Gamete Res 14:107–121]. Using fura-2, we demonstrated that this Sephadex G-75 fraction also stimulates a rapid, transient increase in intracellular free Ca2+. This Ca2+ transient is blocked either by chelation of extracellular calcium or by addition of the Ca2+ antagonist La3+. We have also been able to stimulate the acrosome reaction in human sperm without significant loss of motility, using the divalent cation ionophore ionomycin. Acrosome reactions stimulated by whole follicular fluid, the G-75 fraction, or ionomycin are all blocked by removal of extracellular Ca2+. These results strongly suggest that an influx of extracellular Ca2+ is responsible for intiating the acrosome reaction in human sperm treated with human follicular fluid. This is the first demonstration in mammalian sperm that a potentially physiological stimulus can cause an increase in intracellular Ca2+ concomitant with the acrosome reaction. 相似文献
213.
Development and characterization of continuous avian cell lines depleted of mitochondrial DNA 总被引:6,自引:0,他引:6
Réjean Morais Paul Desjardins Chanta Turmel Karen Zinkewich-Péotti 《In vitro cellular & developmental biology. Plant》1988,24(7):649-658
Summary Populations of quail and chicken cells were treated with ethidium bromide, an inhibitor of mitochondrial DNA replication.
After long-term exposure to the drug, the cell populations were transferred to ethidium bromide (EtdBr)-free medium, and cloned.
Clones HCF7 (quail) and DUS-3 (chicken) were propagated for more than a year, and then characterized. Analysis of total cellular
DNA extracted from these cells revealed no characteristic mitochondrial DNA molecule by Southern blot hybridization of HindIII-
or AvaI-digested total cellular DNA probed with cloned mitochondrial DNA fragments. Reconstruction experiments, where a small
number of parental cells was mixed with HCF7 cells and DUS-3 cells before extraction of total cellular DNA, further strengthen
the notion that the drug-treated cells are devoid of mitochondrial DNA molecules. The cell populations were found to proliferate
at a moderately reduced growth rate as compared to their respective parents, to be auxotrophic for uridine, and to be stably
resistant to the growth inhibitory effect of EtdBr and chloramphenicol. At the ultrastructural level, mitochondria were considerably
enlarged and there was a severe reduction in the number of cristae within the organelles and loss of cristae orientation.
Morphometric analysis revealed a fourfold increase of the mitochondrial profile area along with a twofold decrease of the
numerical mitochondrial profiles. Analysis of biochemical parameters indicated that the cells grew with mitochondria devoid
of a functional respiratory chain. The activity of the mitochondrial enzyme dihydroorotate dehydrogenase was decreased by
95% and presumably accounted for uridine auxotrophy.
This work was supported by a grant from the Medical Research Council of Canada. 相似文献
214.
215.
Paul H. Gumerlock Benjamin F. Edwards Arline D. Deitch Frederick J. Meyers 《In vitro cellular & developmental biology. Plant》1988,24(5):429-434
Summary A human cell line has been established from a renal adenocarcinoma rib metastasis of a 58-y-old male. This cell line has been
maintained in continuous culture for 20 mo. through more than 50 passages. It displays simulataneous expression of the intermediate
filaments cytokeratin and vimentin. Flow cytometric analysis of DNA content reveals a major hyperdiploid population.
This work was supported in part by a grant from Triton Biosciences, Inc. 相似文献
216.
Paul N. Newton 《Plant Ecology》1988,75(1-2):3-16
The vegetation structure and phenology of a 74.5 ha block of moist deeiduous forest in Kanha Tiger Reserve, Madhya Pradesh, India were investigated during primatological fieldwork. Within a grid of 0.25 ha quadrats all 9935 trees (woody plants > 2 m tall), of 63 species, were enumerated and their girth measured. The forest was dominated by the dipterocarp sal (Shorea robusta). Most species were rare and showed clumped distributions within the sea of sal whilst the dispersion of five large canopy trees could not be distinguished from random.The phenology of 215 trees, of 61 species, was monitored over 14 months using an index of phytophase abundance. Leaf renewal was highly synchronous between and within species, mostly occurring between February and June. One species was evergreen, 5 were semi-evergreen and 55 were deciduous. Flowering generally occurred between leaf fall and flush whilst fruiting peaked late in the hot weather and early monsoon. 相似文献
217.
The longest continuous Amazonian palynological record (ca 7010 yrs B.P. to present) from Lake Ayauchi, Ecuador, reveals species-by-species abundance changes during a period of climatic change. Pollen influx from a wet tropical rain forest was found to be high, 1×104–105 grains cm-2 yr-1, although mature forest taxa were poorly represented. Horizons of laminated sediments and weathered gyttja, dated to ca 4200–3150 B.P., evidence a period of reduced net water availability. During this period Ficus, Alchornea and Palmae pollen representation appears to decline, although there is no evidence of a major forest compositional change. The lake was reduced to a shallow, possibly seasonal, pool. Zea cultivation was recorded between ca 2850 B.P., (the earliest paleoecological record to date in the Amazon basin) and ca 800 B.P. It is suggested that Zea was cultivated on exposed lake sediment within the crater at times of low water levels. The abandonment of Zea cultivation may have been due to rising water levels or social unrest. 相似文献
218.
One of the few important empirical generalizations regarding herbaceous plant systems has been the demonstration that species richness is related to standing crop with maximum richness occurring at moderate levels of standing crop. This relationship is normally demonstrated by comparing among vegetation types (i.e., vegetation with different dominants). We undertook this study to test whether the species richness-standing crop relationship was evident at a finer-grained level of organization, the within vegetation type level. Fifteen wetland sites were sampled in eastern Canada and species richness and standing crop determined in each of 224 0.25 m2 quadrats. Each site was relatively homogeneous in terms of the dominant species present and were therefore categorized as single vegetation types. However, as a group, the sites comprised a wide range of vegetation types.A second order polynomial regression indicated a significant bitonic relationship between species richness and standing crop at the among-vegetation types scale, that is, when all 15 sites were combined. At the within-vegetation type level, however, no significant relationships were observed (p>0.05). The results indicate that the model of species richness proposed by Grime has predictive power at a coarse-grained level of organization, among vegetation types, but does not survive the transition to a finer-grained level of organization, the within vegetation type level. Therefore, the higher level processes which structure species richness patterns among vegetation types are not the same processes which determine richness patterns within a vegetation type. 相似文献
219.
220.
Menzel PT 《Bioethics》1992,6(2):158-165
[In his review essay in this issue of Bioethics,] Julian Savulescu lucidly summarizes and assesses each essay in Strong Medicine. I would like to clarify a few important general points about prior consent as a conceptual framework for the ethical rationing of health care, correct several specific misreadings, and defend my basic claim despite some acknowledged problems. 相似文献