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31.
Mechanisms of regulation of the Na+/H+ exchanger 总被引:30,自引:0,他引:30
32.
John R. Spence 《Oecologia》1986,70(1):68-76
Summary Impacts of predators, food levels and cannibalism on population growth of G. buenoi were studied in two experiments using field exclosures. In the first experiment, experiments using field exclosures. In the first experiment, impacts of (1) predation by freshwater invertebrates and (2) food limitation on gerrid populations were considered in a 2 x 2 factorial design, using food supplements and elimination of predators as the experimental treatments. In the second experiment, the possible contribution of intraspecific predation to fitness of gerrid cannibals was assessed.Presence of invertebrate predators decreased egg-adult survivorship 2–3 fold and decreased the range of juvenile development times. The main predators noted in this study were fishing spiders (Dolomedes), backswimmers (Notonecta), larvae of predaceous diving beetles (Dytiscus), and dragonfly naiads (Aeshna). Food supplements, at 50–200% (by weight) of average natural surface fall, did not significantly effect survivorship but were associated with decreases in mean development time and with increases in whole body dry mass of teneral adults. Increases were greater for females than for males, suggesting that females are more likely to be protein limited under field conditions. Absence of predators was associated with smaller body size among teneral adults of G. buenoi, suggesting that screening out aquatic predators also had significant impact on food available to semi-aquatic bugs.Results of the second experiment demonstrate that the food cache hypothesis (Polis 1980) does not hold for G. buenoi. Neither survival to the adult stage nor dry mass of teneral males differed significantly between groups with or without access to early stages as potential prey. Dry mass of teneral females with access to younger stages during their own development was significantly less than for those without access to gerrid prey, suggesting that competition among stages for food was more important than cannibalism in, this experiment.A more comprehensive version of a paper presented at the XVII Int Cong Entomol, Hamburg, Federal Republic of Germany as part of a symposium entitled Phylogeny, Bionomics and Ecology of Waterstriders (Hemiptera, Gerridae) 相似文献
33.
Summary Studies on levels of lead and cadmium of Indian flue-cured tobacco indicated that the leaf contained very low amounts of these
heavy metals as compared to tobacco from other countries. Indian tobacco can therefore be adjudged as ‘safe and clean’ and
least hazardous to the smoker. Of the two heavy metals, lead content of soils is higher than cadmium. But in the leaf, cadmium
content is more than lead indicating that soil cadmium may be more available to tobacco and hence more readily absorbed by
the plant than lead. 相似文献
34.
The cytoplasmic resistivities and membrane breakdown potentials of normal (AA), sickle-cell-trait (AS), and sickle (SS) red
blood cells have been measured by the biophysical methodology of resistive pulse spectroscopy over a range of osmolalities.
At isotonicity, the average membrane breakdown potentials are virtually identical for the three types of cells occurring at
about 1150 V/cm. Average isotonic cytoplasmic resistivities are somewhat higher for the SS cells (166.7±7.49 ohm-cm) compared
to the AA (147.6±1.98 ohm-cm) or AS cells (148.7±1.79 ohm-cm). As medium osmolality is varied, the differences in resistive
properties become enlarged, especially at very low and very high osmolalities. At high osmolalities, both types of sickle
cells show a large increase in internal resistivity compared to the normals; at low osmolality, the SS samples exhibit a distinctly
different membrane breakdown characteristic, decreasing in this parameter, whereas the other two groups increase.
Of the 15 SS samples tested, three displayed much higher cytoplasmic resistivities at isotonicity: 218.2±5.25 ohm-cm, compared
to an average of 153.5±3.46 ohm-cm for the other 12. The relationship between these high resistivities and the subfraction
of irreversibly sickled cells in the sample is discussed. 相似文献
35.
36.
Early mouse embryos produce and release factors with transforming growth factor activity 总被引:2,自引:0,他引:2
Angie Rizzino 《In vitro cellular & developmental biology. Plant》1985,21(9):531-536
Summary Previous studies have shown that extracts from mouse embryos at mid and late stages of development contain factors that exhibit
transforming growth factor activity. The work reported here demonstrates that cultured mouse embryos at significantly earlier
stages of development produce and release factors that exhibit the characteristic property of transforming growth factors.
Specifically, the data demonstrate that embryos cultured from the blastocyst stage in serum-containing medium or in serum-free
medium release factors that promote the anchorage-independent growth of normal rat kidney fibroblasts. It is shown that these
factors are produced and released by cells derived from the inner cell mass and by trophoblasts. The precise developmental
stage when production of these factors first begins has not been determined but our findings suggest that these factors are
produced by cell types associated with early postimplatation embryos.
This work was supported by the Laboratory of Viral Carcinogenesis at the National Cancer Institute and by grants from the
National Cancer Institute (CA-36727) and the University of Nebraska Medical Center (22-271-732).
Editor's Statement This paper presents evidence that, in an in vitro assay system, early embryonic cells are capable of both
synthesizing and secreting TGF-like growth factors, implicating the production of these factors in the events of early development.
David W. Barnes 相似文献
37.
38.
Meiofauna of a sewage-polluted sandy beach, where sand alone constituted > 90%, was surveyed. Nematodes dominated the fauna
numerically at all stations, followed by harpacticoid copepods. Most of the animals were confined to the top 5 cm of the sediment.
A seasonal pattern was observed in the distribution of the fauna. There were significant spatial and temporal variations in
mean meiofauna density, attributed to organic discharge via sewage and prevailing environmental conditions in the study area. 相似文献
39.
Hiroyoshi Hoshi Mikio Kan Wallace L. McKeehan 《In vitro cellular & developmental biology. Plant》1987,23(10):723-732
Summary Hepatocytes were isolated from human fetal liver in order to analyze the direct effects of growth factors and hormones on
human hepatocyte proliferation and function. Mechanical fragmentation and then dissociation of fetal liver tissue with a collagenase/dispase
mixture resulted in high yield and viability of hepatocytes. Hepatocytes were selected in arginine-free, ornithine-supplemented
medium and defined by morphology, albumin production and ornithine uptake into cellular protein. A screen of over twenty growth
factors, hormones, mitogenic agents and crude organ and cell extracts for effect on the stimulation of hepatocyte growth revealed
that EGF, insulin, dexamethasone, and factors concentrated in bovine neural extract and hepatoma cell-conditioned medium supported
attachment, maintenance and growth of hepatocytes on a collagen-coated substratum. The population of cells selected and defined
as differentiated hepatocytes had a proliferative potential of about 4 cumulative population doublings. EGF and insulin synergistically
stimulated DNA synthesis in the absence of other hormones and growth factors. Although neural extracts enhanced hepatocyte
number, no effect on DNA synthesis of neural extracts or purified heparin-binding growth factors from neural extracts could
be demonstrated in the absence or presence of defined hormones, hepatoma-conditioned medium or serum. Hepatoma cell-conditioned
medium had the largest impact on both hepatocyte cell number and DNA synthesis under all conditions. Dialyzed serum protein
(1 mg/ml) at 10 times higher protein concentration had a similar effect to hepatoma cell-conditioned medium (100 μg/ml). The
results suggest that hepatoma cell conditioned medium may be a concentrated and less complicated source than serum for purification
and characterization of additional normal hepatocyte growth factors.
This work was supported by NIH grant DK35310.
Editor’s statement Many investigators have struggled with the special problems associated with culture of differentiated hepatocytes.
In this paper attention is given to the specific growth factor requirements for fetal human hepatocytes. The observation that
factors from hepatoma conditioned medium or neural extracts enhanced the growth of the cells may indicate that additional
growth factors are to be identified that are important in the survival and proliferation of hepatocytes, and may also indicate
that the malignant transformation of these cells may involve the production of autocrine growth stimulators. 相似文献
40.
Different hormonal requirements for androgen-independent growth of normal and tumor epithelial cells from rat prostate 总被引:4,自引:0,他引:4
Wallace L. McKeehan Pamela S. Adams Danna Fast 《In vitro cellular & developmental biology. Plant》1987,23(2):147-152
Summary The proliferation of isolated normal prostate epithelial cells from rat and man is androgen-independent and requires cholera
toxin, insulin, dexamethasone, epidermal growth factor (EGF) and one or more polypeptide factors that are concentrated in
bovine neural tissue. The active agents in the neural tissue extract are heparin-binding polypeptides (prostatropins), the
predominant form of which has a molecular weight of 17400 and an acetylalanine at the aminoterminus. Prostatropins supported
a half-maximal increase in normal prostate epithelial cell number at 50 picomolar. The proliferation of primary and serially-cultured
epithelial cells from androgen-responsive Dunning R3327 rat prostate tumors was also androgen-independent, but exhibited dramatic
alterations in response to hormones that stimulated normal cell proliferation. At low cell density, androgen-independent growth
of isolated tumor-derived epithelial cells was independent on cholera toxin, was stimulated by dexamethasone, required insulin
andeither EGFor prostatropin. The presence of either EGF or prostatropin masked the response to the other factor. In the absence of EGF,
purified prostatropins supported a half-maximal increase in tumor cell number at 7 picomolar. Endogenous production of EGF-like
and prostatropin-like factors or both was suggested by the reduced requirement for EGF and prostatropin at high prostate tumor
cell density. These results suggest that anti-hormonal therapies against prostate tumor growth should be based on intervention
with the activity of insulin (or insulin-like factors) or simultaneous intervention with both EGF and prostatropin (or their
homologues).
This work was supported by NIH grants CA 37589 and HL 33847, and grant 1718 from the Council for Tobacco Research.
Editor’s Statement This paper is the first report of the comparison of the hormone requirements of primary cultures of normal
and tumor prostate epithelial cells from the same system. 相似文献