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51.
Pamela D. Arora Kathryn J. Bibby Christopher A. G. McCulloch 《Journal of cellular physiology》1994,161(2):187-200
Calcium transients in single, human gingival fibroblasts were studied after mechanical stretching of flexible culture substrates. A model system was developed to reproducibly stretch and rapidly (< 1 sec) refocus cells in the same focal plane so that changes in the concentration of free intracellular calcium ions ([Ca2+]i) were monitored without delay. Attached cells were grown on flexible bottom Petriperm dishes, loaded with fura-2/AM, and stretched by 1% or 2.8% of substrate area. The stretch caused no significant cell detachment or membrane lesions. A 1% stretch induced no calcium response, but a 2.8% stretch stimulated an initial calcium transient and the subsequent generation of [Ca2+]i oscillations of up to 2,000 sec. At 1% stretch, there was no calcium response. Cell shape and plating time were important determinants in the calcium response to mechanical stimulation: the responder cells were small and round without long processes. Major calcium transients were inhibited completely by 5 mM EGTA or by 10 μM gadolinium ions, by 50 μM nifedipine, or 250 μM verapamil, suggesting an influx of calcium through stretch-activated (SA) channels and L-type calcium channels. Depolarization by high KCl (144 mM) in the extracellular medium enhanced the amplitude of calcium transients by 54%. Calcium oscillations were not inhibited by preincubation with thapsigargin, caffeine, cholera toxin, staurosporine or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), indicating that IP3 sensitive pools, IP3 insensitive pools, G5α subunits, and protein kinase C, respectively, were not involved in the generation of calcium oscillations. Pretreatment with genistein, a specific tyrosine kinase inhibitor or cytochalasin D, an inhibitor of actin polymerization, or pertussis toxin, an inhibitor of Giα and Goα subunits, completely abolished calcium transients and oscillations. These results indicate that Ca2+ flux due to mechanical stretching is likely mediated through SA ion channe s and is dependent on tyrosine kinases, pertussis toxin-sensitive subunits of G-proteins, and actin filaments. © 1994 Wiley-Liss, Inc. 相似文献
52.
John A. Lowe III Weimin Qian Pamela J. Scott Stafford McLean Dianne K. Bryce Rosemary T. Crawford Jon Bordner 《Bioorganic & medicinal chemistry letters》1994,4(24):2877-2882
A series of 5,7-diphenyl-3-ureidohexahydroazepin-2-one cholecystokinin-B (CCK-B) receptor antagonists was synthesized using Beckmann ring expansion of a suitable 2,4-diphenylcyclohexanone as a key step. SAR studies revealed the importance of the 5-aryl group for high and selective CCK-B receptor affinity, as illustrated in compound (−)-10i (CCK-B IC50 = 6.8 nM). 相似文献
53.
Summary We used in vitro growth inhibition assays to demonstrate that synthetic cecropin protein has potent activity against a range of plant pathogenic bacteria. We then prepared transgenic tobacco plants which express cecropin mRNA and protein. We have used Pseudomonas syringae pv tabaci infection of these transgenic tobacco as a model system to evaluate whether the plants which express cecropin protein also have increased tolerance to infection. We found no dramatic difference in disease response between plants which are expressing cecropin protein and control plants which were derived from the transformation with a binary vector which did not carry the gene encoding cecropin protein. 相似文献
54.
55.
Regulation of nitrate uptake by amino acids in maize cell suspension culture and intact roots 总被引:3,自引:0,他引:3
The effect of amino acids on nitrate transport was studied in Zea mays cell suspension cultures and in Zea mays excised roots. The inclusion of aspartic acid, arginine, glutamine and glycine (15mM total amino acids) in a complete cell-culture media containing 1.0 mM NO3
- strongly inhibited nitrate uptake and the induction of accelerated uptake rates. The nitrate uptake rate increased sharply once solution amino acid levels fell below detection limits. Glutamine alone inhibited induction in the cell suspension culture. Maize seedlings germinated and grown for 7 days in a 15 mM mixture of amino acids also had lower nitrate uptake rates than seedlings grown in 0.5 mM Ca(NO3)2 or 1 mM CaCl2. As amino acids are the end product of nitrate assimilation, the results suggest an end-product feed-back mechanism for the regulation of nitrate uptake. 相似文献
56.
Alexander A. DiIorio Pamela J. Weathers Ronald D. Cheetham 《Applied microbiology and biotechnology》1993,39(2):174-180
Transformed root tissue of Beta vulgaris (Detroit Dark Red) was permeabilized to stimulate the release of intracellularly stored betanin without adverse affects on tissue viability as measured by biomass accumulation. Product release of up to 15% (w/w) was achieved by heat treatment at 42°C for 45 min with minimal effect on viability. Higher levels of product release were obtained with increasing temperature and exposure, but at the expense of viability. Viability was measured by comparing dry weight increases of permeabilized tissue 3 days after treatment vs non-permeabilized tissue over the same time interval. Recovery of heat-treated tissue was improved by addition of CaCl2 (20 mm for 10 min) post-heat treatment. Betanin release up to 15% was also obtained at ambient temperature (25°C) by addition of up to 20 mm (NH4)2SO4 in the presence of 1 mm ethylenediaminetetraacetic acid (EDTA).
Correspondence to: A. A. DiIorio 相似文献
57.
58.
Pamela K. Diggle 《American journal of botany》1993,80(8):967-973
Studies of andromonoecious species have shown that sex expression (proportions of hermaphrodite and staminate flowers) is quite variable. It is not known, however, whether this variation is due to variation among individuals for genetically fixed patterns of allocation to staminate and hermaphrodite flowers (population level variation) and/or to developmental plasticity of individuals in a heterogeneous environment (organismal level variation). Distinguishing between these two levels of variation is important for understanding the evolution of andromonoecy. This study investigates levels of variation in sex expression in the andromonoecious Solanum hirlum. Sex expression in this species is shown to be plastic among individuals of the same genotype (organismal level variation) and determined, in part, by the resource status of the individual. Among the genotypes examined there is also genetic variation for developmental plasticity. Thus, developmental plasticity can potentially respond to selection, and the evolution of this developmental system may have been instrumental in the establishment and maintenance of andromonoecy in S. hirtum. 相似文献
59.
Aspects of the biology of Pantinonemertes californiensis,a high intertidal nemertean 总被引:3,自引:3,他引:0
Pamela Roe 《Hydrobiologia》1993,266(1-3):29-44
I studied the distribution, feeding biology, and reproductive biology of Pantinonemertes californiensis, described as a semi-terrestrial nemertean, along the central California coast. At the sites used in this study, maximal
tidal height is about 2 m, and P. californiensis typically occurred under boulders between 1.3 and 1.7 m tidal height. Worms fed primarily on the semi-terrestrial amphipod
Traskorchestia traskiana. Distribution of nemerteans was similar to that of the prey, although prey extended higher on the beach than did the worms.
Nemerteans were largest and most abundant at the site with highest abundance of T. traskiana and smallest and least abundant at the lowest prey abundance site. In laboratory feeding trials, nemerteans from the site
with lowest prey abundance fed most readily. Non-reproductive nemerteans lived for at least a week when submerged in sea water;
some prey died within a week of being submerged. Nemerteans only lived minutes when submerged in fresh water; 50% of prey
lived 4.5 h. Eggs are approximately 90–100 μm in diameter and hundreds to thousands are shed per female. Larvae are planktonic
and apparently planktotrophic, and are morphologically similar to other marine hoplonemertean larvae. At the sites studied
life history characteristics of P. californiensis provided little evidence of adaptations to terrestrial life in these worms and were not helpful in elucidating the role of
semi-terrestrial nemerteans in the evolution of terrestrial nemerteans. 相似文献
60.
Niraj Shrestha Pallavi Chaturvedi Xiaoyun Zhu Michael J. Dee Varghese George Christopher Janney Jack O. Egan Bai Liu Mark Foster Lynne Marsala Pamela Wong Celia C. Cubitt Jennifer A. Foltz Jennifer Tran Timothy Schappe Karin Hsiao Gilles M. Leclerc Lijing You Christian Echeverri Catherine Spanoudis Ana Carvalho Leah Kanakaraj Crystal Gilkes Nicole Encalada Lin Kong Meng Wang Byron Fang Zheng Wang Jin-an Jiao Gabriela J. Muniz Emily K. Jeng Nicole Valdivieso Liying Li Richard Deth Melissa M. Berrien-Elliott Todd A. Fehniger Peter R. Rhode Hing C. Wong 《Aging cell》2023,22(5):e13806