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61.
Summary A suspension of tobacco cells,Nicotiana tabacum L. BY-2, was subjected to a rapid change of medium, resulting in disturbance of growth. A subpopulation of growing cells responded to such a nutritional signal by establishing a transient, localized Ca2+ accumulation, as judged by chlorotetracycline fluorescence. Residing near or at the plasma membrane, this initial Ca2+ signal began to relax after 1 h to a value presumably corresponding to an equilibrium Ca2+ level. This response was susceptible to treatment with brefeldin A, an agent impacting vesicular traffic, as indicated by a further increase in fluorescence. By contrast, undisturbed growing and non-growing cells did not display a Ca2+ response, regardless of the presence of brefeldin A. 相似文献
62.
Victor D. Ramirez Jianbiao Zheng Khawar M. Siddique 《Cellular and molecular neurobiology》1996,16(2):175-198
Summary 1. There are numerous circumstantial evidence supporting the concept that steroid hormones control cellular function by means other than the nuclear receptor steroid binding mechanism. It is the intent of this report to present evidence indicating that steroids bind to specific sites in neuronal membranes.2. Some of the criteria to define steroid membrane receptors using steroid-BSA conjugates that can be radioiodinated to desired specific activity have been fulfilled for each of the three sex steroids using crude synaptosomal membrane preparations (P2 fractions) from the CNS of female and male rats. Ligand binding for each of the three steroids indicate high-affinity and high-capacity sites with distinct brain selectivity and stereospecificity. For example, 17-E-6-[125I]BSA binds hypothalamic P2 fractions (HYP-P2) with an estimatedK
d of about 3±0.7 nM (X ± SE;n=3), whereas the cerebellum P2 (CB-P2) fractions bind the ligand with aK
d of 34±7 nM and, aB
max of 3 and 42 pmol/mg protein, respectively. Estrogen and testosterone binding fit best a one-single site, while progesterone binding sites can be best represented by a two-binding site, one high-affinity (K
d=1–2 nM) and one low affinity (K
d=62 nM), in CB-P2 fractions from intact adult female rat brain. Kinetics studies for T-3-[125I]BSA indicate that the estimatedK
d of 30±2 nM for the olfactory bulb P2 fractions (OB-P2) from male rats is in good agreement withK
d values computed from Scatchard-derived data using the LIGAND algorithm.3. 17-E-6-[125I]BSA binding sites are stereospecific and appears to be present as early as 5 days of age in both the OB- and the CB-P2 fractions without changes during development. In contrast, P-6-[125I]BSA binding sites are practically absent during days 5 and 12 and appear by day 22.4. Finally, membrane receptor molecules for estrogen and progesterone have been isolated and purified by affinity chromatography and characterized by PAGE and Western blot. Microsequencing of one of the membrane estrogen binding proteins indicates that the high-affinity site corresponds to the OSCP subunit of the proton ATP synthase.5. It remains to be determined if P and T also bind to this complex enzyme or if they bind to other subunits of the family of proton ATPases. Overall the data indicate that steroid hormones conjugated to BSA are important tools to study the reality of membrane steroid receptors. 相似文献
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64.
Short-term aluminium uptake by tobacco cells: Growth dependence and evidence for internalization in a discrete peripheral region 总被引:1,自引:0,他引:1
Short-term uptake and initial localization of aluminium (Al) were investigated in cultured cells of Nicotiana tabacum L. cv. BY-2. Graphite furnace atomic absorption spectrometry and an in vivo Al-sensitive fluorometric assay, employing morin, yielded similar results in all experiments. Aluminium uptake was critically dependent on cell growth. As opposed to negligible uptake in stationary-phase cells, Al uptake (20 μ M AlCl3 , pH 4.5, 23°C) by actively growing cells was detectable within 5 min, with an initial rate of 16 nmol Al (106 cells)−1 h−1 . Increased CaCl2 levels (up to 20 m M ), low temperature (4°C), and pre-chelation of Al to citrate greatly reduced Al uptake (by 75–90%). A pH-associated permeabilization of cells at pH 4.5, as monitored by trypan blue, was observed in some growing cells. Although permeability to trypan blue was not a requirement for Al uptake, enhanced membrane permeability at pH 4.5, relative to pH 5.6, may contribute to Al uptake. Aluminium was observed to localize mainly in a pronounced and discrete fluorescent zone at the cell periphery (2–30 μm wide), presumably in the cortical cytosol and/or the adjoining plasma membrane section, although the possibility cannot be excluded that some Al resided in the cell wall apposing this discrete region. However, as judged by the Al-morin assay, there were no detectable Al levels in the remaining, larger portion of the cell wall. The potential of the Al-morin method in Al toxicity studies is illustrated. 相似文献
65.
Kailash Prasad Victor A. Laxdal Ming Yu Barbara L. Raney 《Molecular and cellular biochemistry》1996,165(1):55-63
While antibiotics are broadly used in dental and medical therapy, little attention has been directed towards the potential toxic side effects of antibiotics on tissue regeneration. Here we examined the effect of a quinolone antibiotic, pefloxacin (Rhone Poulenc) on rat parotid gland responses to chronic isoproterenol treatment. Groups of rats received injections of isoproterenol to induce glandular growth, saline (controls), pefloxacin, or isoproterenol and pefloxacin in combination. Parotid gland weight decreased significantly after pefloxacin treatment for 7 days as well as inhibiting glandular enlargement provoked by isoproterenol. The same trend was observed for the rates of DNA synthesis, with the incorporation of [3H]-thymidine in isoproterenol/pefloxacin-treated rats reduced to 49% of isoproterenol treatment alone levels. Saline-treated animals were 42% of the rate of [3H]-thymidine incorporation into DNA observed in isoproterenol treated rats. While isoproterenol treatment increased steady-state mRNA levels for fos, jun, myc, src, c-erbB-2, ras and topo II, inclusion of pefloxacin with the isoproterenol regimen blocked these increases. Pefloxacin treatment by itself did not alter proto-oncogene mRNA levels in the parotid gland. Glandular amylase activity was decreased in the pefloxacin treated group, while the combination of isoproterenol with pefloxacin did not decrease glandular amylase levels to the extent of that observed with -agonist treatment alone. In acute experiments, pefloxacin significantly decreased the volume of saliva secreted by the parotid gland. These results suggest that quinolone-based antibiotics disturb the secretory function of the parotid gland and can inhibit cell proliferation and regeneration. (Mol Cell Biochem 165: 55–63, 1996) 相似文献
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68.
We describe the traditional production system of the root of jalapa, Ipomoea purga, in Xico, Veracruz, Mexico. The results are based on open interviews with the producers to gather information on the development of this crop in the area, and observation of the production system. The production cycle is carried out between July and February. We found that seed scarification is the key to the success of the productive system, obtaining a maximum of 95% seed germination in eight days. This activity, as well as seed collection and the driving of stakes into the ground for plant support, requires a considerable input of man-power. It is an intensive farming process, the cultivated area per farmer varies between 300 m2 and 1000 m1, and the yield ranges between 1.5 and 2.7 tons per hectare of fresh roots; when dried they lose up to 75% of their weight. Smoke-dried roots are exported for sale. 相似文献
69.
A combinatorial sequence space (CSS) model was introduced to represent sequences as a set of overlapping k-tuples of some fixed length which correspond to points in the CSS. The aim was to analyze clusterization of protein sequences in the CSS and to test various hypotheses about the possible evolutionary basis of this clusterization. The authors developed an easy-to-use technique which can reveal and analyze such a clusterization in a multidimensional CSS. Application of the technique led to an unexpectedly high clusterization of points in the CSS corresponding to k-tuples from known proteins. The clusterization could not be inferred from nonuniform amino acid frequencies or be explained by the influence of homologous data. None of the tested possible evolutionary and structural factors could explain the clusterization observed either. It looked as if certain protein sequence variations occurred and were fixed in the early course of evolution. Subsequent evolution (predominantly neutral) allowed only a limited number of changes and permitted new variants which led to preservation of certain k-tuples during the course of evolution. This was consistent with the theory of exon shuffling and protein block structure evolution. Possible applications of sequence space features found were also discussed.Correspondence to: H.A. Lim 相似文献
70.