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21.
The effects of procedures which diminish Ca2+ influx into myocardial cells on responses of isolated cardiac preparations to cAMP-independent histamine H1 receptor stimulation and cAMP-generating beta-receptor stimulation were measured. The histamine response of guinea pig left atria, which appears to be primarily mediated by H1 receptors, was depressed to a greater extent than was the response of this preparation to isoproterenol by decreasing the extracellular Ca2+ concentration, and by the Ca2+ influx blocker D-600. Similarly, while the H1 agonist 2-pyridylethylamine dihydrochloride (PEA) produced increases in tension of a similar magnitude as the partial beta-agonist salbutamol in both left atria and in papillary muscles, responses of both preparations to PEA were depressed to a significantly greater extent by decreasing the extracellular Ca2+ concentration than were responses to salbutamol. Overall, both the basal developed force of papillary muscles and the responses of these preparations to H1 and beta-receptor stimulation appeared to be less depressed by decreasing the extracellular Ca2+ concentration than were those of left atria. These results indicate that responses mediated via cAMP-independent H1 receptors, like those arising from alpha-receptor stimulation, are more sensitive to procedures which diminish Ca2+ influx than are responses arising from stimulation of cAMP-generating beta-receptors. This may reflect differences in the mechanisms by which stimulation of H1, alpha-, and beta-receptors give rise to positive inotropic responses. In addition, left atria may be more dependent than papillary muscles on extracellular Ca2+ for the support of contraction. 相似文献
22.
T-cell-mediated regression of "spontaneous" and of Epstein-Barr virus-induced B-cell transformation in vitro: studies with cyclosporin A 总被引:15,自引:0,他引:15
A B Rickinson M Rowe I J Hart Q Y Yao L E Henderson H Rabin M A Epstein 《Cellular immunology》1984,87(2):646-658
The regression of Epstein-Barr (EB) virus-transformed B-cell outgrowth which is seen in experimentally-infected cultures of blood mononuclear (UM) cells from healthy seropositive donors can be abolished in medium containing the T-cell-suppressive agent cyclosporin A (CSA) at concentrations of 0.05 microgram/ml and above. CSA mediates its effect within the first 4 days post-infection of the UM cells and this prevents subsequent in vitro generation of the EB virus-specific cytotoxic-T-cell response which normally brings about regression. Regression can be fully restored by supplementing the CSA-treated culture with interleukin 2 (IL-2)-containing culture supernatants or indeed with purified IL-2 itself, suggesting that CSA mediates its effect in this system through inhibiting the endogenous production of IL-2 which is required to amplify the virus-specific cytotoxic response. "Spontaneous transformation" to EB virus genome-positive lymphoblastoid cell lines in noninfected cultures of UM cells from healthy seropositive donors, though rare in normal medium, is enhanced to such a degree in the presence of CSA that, for many donors, the phenomenon becomes titratable against input cell dose across the 2.0 X 10(6)-2.5 X 10(5) cells/culture range. Cell mixing experiments suggest that the spontaneously transformed cell lines which arise with such efficiency under these conditions do so not by direct in vitro outgrowth of progenitor cells transformed by the virus in vivo, but by a two-step mechanism involving virus release and secondary infection in vitro. 相似文献
23.
R M Kamp Z J Yao B Wittmann-Liebold 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1983,364(2):141-155
Tryptic peptides of the ribosomal proteins S11, L9 and L29 were separated by reversed phase chromatography under conditions which enabled direct micro-sequencing with the 4-(dimethylamino)azobenzene-4'-isothiocyanate/phenylisothiocyanate double coupling method [Chang, Brauer, Wittmann-Liebold (1978) FEBS Lett. 93, 205-214]. The peptides were separated on a RP-18 column employing volatile buffers at pH 2.0, 4.1 and 7.8. Depending on the different chromatographic behaviour of the peptide mixture, the elution gradient was optimised for each hydrolysate using 20 micrograms of the hydrolysed protein. Preparative separations were made with 150-250 micrograms. At least 80% of the peptides could be isolated by these techniques and used for direct micro-sequencing without further purification or desalting. The results show that the high-performance liquid chromatographic method employed allows easy isolation and sequencing with minute amounts of peptides. 相似文献
24.
Purification of Escherichia coli 30S ribosomal proteins by high performance liquid chromatography 总被引:1,自引:0,他引:1
R M Kamp Z J Yao A Bosserhoff B Wittmann-Liebold 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1983,364(12):1777-1793
High performance liquid chromatography was applied to the separation of proteins derived from the Escherichia coli 30S ribosomal subunit. Several methods of separating this protein mixture has been tested: size-exclusion chromatography on hydrophilic phases; ion exchange and reversed phase chromatography (on C2 to C18 hydrocarbon-bonded supports). Various elution systems were examined in order to obtain pure proteins suitable for micro-sequence analysis. The resolution and yields of the proteins varied considerably, depending on the type of support and gradient system used. The best results were achieved with uniformly globular-shaped supports of large pore size, and by combining high performance size exclusion with rechromatography on reversed phase columns. Purification conditions for the individual proteins are listed. The methods employed avoid any precipitation step and allow easy identification of the proteins by one or two-dimensional gel electrophoresis, amino-acid analysis or direct manual or automatic micro-sequencing. Since the isolation time is much reduced compared with conventional purification procedures, the proteins obtained by the techniques described here are well suited for topographical and immunological studies or reconstitution assays. Ribosomal proteins of other organisms can be separated under similar conditions. 相似文献
25.
14C-Sterigmatocystin isolated from cultures of supplemented with (1-14C)acetate was shown to be efficiently converted to aflatoxin B1 by the resting mycelium of . The experimental results may indicate a biosynthetic pathway leading from 5-hydroxysterigmatocystin to sterigmatocystin and then to aflatoxin B1. 相似文献
26.
27.
人肝癌细胞表皮生长因子受体以及佛波酯对它的调度 总被引:1,自引:0,他引:1
Using radioligand binding assay, the presence of epidermal growth factor (EGF) receptors in cells of two human liver cancer cell lines, BEL-7402 and SMMC-7721, was demonstrated. The ligand binding data were analyzed by a computer program. The dissociation constants (KD) of the ligand-receptor binding complex at equilibrium for 7402 and 7721 cells were 1.2 nM and 0.8 nM respectively, and their number of EGF receptors per cell were 6.2 x 10(4) and 2.5 x 10(4) respectively. After the treatment of cells with phorbol 12-myristate 13-acetate (PMA), no change either in the affinity or in the number of EGF receptors was found in 7721 cells. However, in the case of 7402 cells, while the number of receptors, like 7721 cells, remained unchanged, the affinity of EGF receptors displayed a time dependent modulation after PMA treatment. It dropped within the first hour to a KD value of 3.0 nM and then gradually returned to the normal control value at 48 hours or even slightly higher than normal (0.95 nM) at 96 hours of treatment. The modulation or down-regulation of EGF receptors by PMA in 7402 cells was paralleled by the simultaneous inhibition of DNA synthesis in these cells as evidenced from their reduction of 3H-TdR uptake. It is not clear what is the basis for the differences found between 7402 cells and 7721 cells in their number of EGF receptors per cell and their responsiveness to PMA treatment. It might be related to their difference in autocrine secretion of alpha-transforming growth factors.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
28.
29.
鲢、鳙在天然条件下的摄食强度(Ⅱ)武汉东湖鲢、鳙周年摄食强度的研究 总被引:3,自引:0,他引:3
武汉东湖的鲢(Hypophthalmichthy molitrix)鳙(Aristichthys nobilis)在天然条件下摄食强度具季节性变化。摄食强度高峰处于夏季,低谷处于冬季。在实验条件下,按周年采样期间水温变化范围,测定鱼的肠管排空率。食物通过鱼肠管时间(Y_p—h)与水温(X_t—℃)的关系为: 鲢Y_p=270.63 X_t~(0.6408) 鳙Y_p=280.46 X_t~(0.6642) 根据修正后Bajkov公式(D=C (24.A)/n),估算鱼的日粮。鱼日粮(Y_D)与水温(X_t)关系为: 鲢Y_D=0.2683e~(0.1503X_t) 鳙Y_D=0.0075X_t~(2.2715) 计算鱼在天然条件下周年月粮及年粮。鲢、鳙对天然饵料年消耗量分别为18.924公斤及17.39公斤,饵料系数分别为18.02及13.38。 相似文献
30.
Site-specific chromosome breakage occurs in many ciliated protozoa during nuclear differentiation. We have determined the cis-acting sequence that controls this process in Tetrahymena thermophila. The Tetrahymena ribosomal RNA gene is bounded by two breakage sites. Injection of this gene into developing macronuclei leads to breakage at these sites. Deletion analysis has localized the sequences essential for breakage to a 28 bp region that includes a 15 bp sequence (Cbs) known to be present in other breakage sites. Insertions of Cbs allow breakage to occur at new sites, which is accompanied by elimination of surrounding DNAs and formation of telomeric sequences, as it is at natural sites. Thus, Cbs is the necessary and sufficient sequence signal for chromosome breakage in Tetrahymena. 相似文献