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61.
H Klitgaard R Marc A Brunet H Vandewalle H Monod 《Journal of applied physiology》1989,67(4):1401-1408
To examine how different kinds of activity affect the composition and contractile properties of aging skeletal muscle, old male rats were strength and swim trained. The mass of weights lifted during the strength training increased by 85 +/- 9% (P less than 0.05), which was accompanied by an increase by 32 +/- 5% (P less than 0.05) of the estimated force developed. The wet muscle weight of the soleus and the plantaris decreased significantly with age. The phenomenon was counteracted but not neutralized by the strength training. Twitch and tetanic tension also decreased significantly with age in both the soleus and plantaris muscle. This was avoided by the strength training. This training also significantly decreased time to peak tension and half-relaxation time of both muscles. The swim training increased the heart-to-body weight ratio by 21 +/- 5% (P less than 0.05) and the endurance of the soleus muscle. Time to peak tension and triosephosphate dehydrogenase activity of the plantaris muscle were strongly correlated (P less than 0.001) with myosin adenosinetriphosphatase activity. The results show that the composition and contractile properties of old skeletal muscle are considerably affected by strength training repeated during a substantial period of old age, whereas swim training only affects the endurance of the skeletal muscle. 相似文献
62.
Marc Yudkoff David Pleasure Lynn Cregar Zhi-Ping Lin Ilana Nissim Janet Stern Itzhak Nissim 《Journal of neurochemistry》1990,55(1):137-145
The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20-40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady-state incubation medium with 0.05 mM L-cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids. 相似文献
63.
Marc Mangel 《Mathematical biosciences》1990,100(2):241-248
A patch selection game is formulated and analyzed. Organisms can forage in one of H patches. Each patch is characterized by the cost of foraging, the density and value of food, the predation risk, and the density of conspecifics. The presence of conspecifics affects the finding and sharing of food, and the predation risk. Optimal foraging theory can be viewed as a "1-person" game against nature in which the optimal patch choice of a specific organism is analyzed assuming that the number of conspecifics in other patches is fixed. In the general game theoretic approach, the behavior of conspecifics is included in the determination of the distinguished organism's strategy. An iterative algorithm is used to compute the solution of the "n-person" game or dynamic ESS, which differs from the optimal foraging theory solution. Experiments to test the proposed theory using rodents and seed trays are briefly discussed. 相似文献
64.
The organization of microtubules (MTs) in the cortex of cells at interphase is an important element in morphogenesis. Mechanisms
controlling the initiation of MTs and their spatial ordering, however, are largely unknown. Our recent study concerning the
generation of a radial array of MTs in stomatal guard cells inAllium showed that the MTs initiate in a cortical MT-organizing zone adjacent to the ventral wall separating the two young guard
cells (Marc, Mineyuki and Palevitz, 1989, Planta179, 516, 530). In an attempt to detect MT-ordering mechanisms separate from the sites of MT initiation, we now employ various
drugs to manipulate the geometry and integrity of the ventral wall and thereby also the associated MT-organizing zone. In
the presence of cytochalasin D the ventral wall is tilted away from its normal mid-longitudinal anticlinal alignment, while
treatments with the herbicide chloroisopropyl-N-phenylcarbamate (CIPC) induce the formation of a branched ventral wall. Nonetheless, in either case the MTs still
form a radial array, although this is asymmetric as it is centered in accordance with the misaligned or branched ventral wall.
Since the MTs maintain their original course undisturbed as they extend beyond the abnormal ventral wall, there is no evidence
for the presence of an inherent MT-ordering mechanism at locations remote from MT-initiation sites. Following treatments with
caffeine, which abolishes the formation of the ventral wall, the MTs revert to a transversely oriented cylindrical array as
in normal epidermal cells. Thus the presence of the ventral wall, and presumably also the associated MT-organizing zone, is
essential for the establishment of the radial array. The MT-organizing zone is therefore involved not only in the initiation
of MTs, but also in determining their spatial order throughout the cell cortex.
We thank Drs. Richard J. Cyr and Yoshi Mineyuki for providing valueable suggestions during the course of this work, and Ms.
Elizabeth Bruce printing some of the figures. This research was supported by Funds from the National Science Foundation grants
DCB-8703292 to B.A.P. and DCB-8803286 to B.A.P. and J.M. 相似文献
65.
The binding of t-[35S]butylbicyclophosphorothionate [( 35S]TBPS) to a site on the GABAA receptor complex is ion dependent. This study was conducted to determine the effects of ion species and concentration on the time course, affinity, and number of sites of [35S]TBPS binding. At a concentration of 200 mM ion, the time to equilibrium for [35S]TBPS binding was shortest for I-, followed by Br- less than Cl- less than F-. A similar rank order was observed for the concentration of ion required to produce half-maximal [35S]TBPS binding. Saturation binding experiments were conducted to evaluate the effect of increasing ion concentration on the KD and Bmax of [35S]TBPS binding. The Bmax was independent of both ion species and concentration. The receptor affinity, however, increased with increasing concentration for each ion. Calculated maximal affinity values were not different between ions; however, the EC50 to produce those values was different among ions and ranked in the same order as that for time course and maximal binding data. Association and dissociation rates for [35S]TBPS binding were greater in I- than in Cl-. These data emphasize the importance of ion selection and incubation times on [35S]TBPS binding. 相似文献
66.
Marc Parmentier 《Biology of the cell / under the auspices of the European Cell Biology Organization》1990,68(1):43-49
Summary— The distribution of calbindin D28k in the digestive system and the urinary bladder of the toad was investigated using immunohistochemistry and Western blotting. By analogy with mammals and birds, the protein was expected to be located preferentially in the duodenal part of the intestine. Interestingly, absorptive cells of the duodenum were totally devoid of calbindin D28k while the colon contained high amounts of the calcium-binding protein. This reversed polarity of calbindin D28k content in the toad intestine should obviously correspond to a different scheme of calcium absorption regulation between amphibians and higher vertebrates. Calbindin D28k containing neuroendocrine-like cells were found scattered in the proximal parts of the gut with a similar distribution to what has been described in rat and chick intestine. The oesophagus, the stomach, and the intrinsic nervous sytem of the intestine were negative. No significant amounts of the proteins were found in the urinary bladder, which is known to be a site of Ca2+ active transport. 相似文献
67.
Stefan Evers Barbara Casadewall Murielle Charles Sylvie Dutka-Malen Marc Galimand Patrice Courvalin 《Journal of molecular evolution》1996,42(6):706-712
Thed-alanine:d-alanine-ligase-related enzymes can have three preferential substrate specificities. Usually, these enzymes synthesized-alanyl-d-alanine. In vancomycin-resistant Gram-positive bacteria, structurally related enzymes synthesized-alanyl-d-lactate or Dalanyl-d-serine. The sequence of internal fragments of eight structurald-alanine:d-alanine ligase genes from enterococci has been determined. Alignment of the deduced amino acid sequences with those of other
related enzymes from Gram-negative and Gram-positive bacteria revealed the presence of four distinct sequence patterns in
the putative substrate-binding sites, each correlating with specificity to a particular substrate (d-alanine:d-lactate ligases exhibited two patterns). Phylogenetic analysis showed different clusters. The enterococcal subtree was largely
superimposable on that derived from 16S rRNA sequences. In lactic acid bacteria, structural divergence due to differences
in substrate specificity was observed. Glycopeptide resistance proteins VanA and VanB, the VanC-type ligases, and Dd1A and
DdlB from enteric bacteria andHaemophilus influenzae constituted separate clusters.
Correspondence to: P. Courvalin 相似文献
68.
Extracellular matrix regulation of intestinal epithelial differentiation may affect development, differentiation during migration to villus tips, healing, inflammatory bowel disease, and malignant transformation. Cell culture studies of intestinal epithelial biology may also depend on the matrix substrate used. We evaluated matrix effects on differentiation and proliferation in human intestinal Caco-2 epithelial cells, a model for intestinal epithelial differentiation. Proliferation, brush border enzyme specific activity, and spreading were compared in cells cultured on tissue culture plastic with interstitial collagen I and the basement membrane constituents collagen IV and laminin. Each matrix significantly increased alkaline phosphatase, dipeptidyl peptidase, lactase, sucrase-isomaltase, and cell spreading in comparison to plastic. However, the basement membrane proteins collagen IV and laminin further promoted all four brush border enzymes but inhibited spreading compared to collagen I. Proliferation was most rapid on type I collagen and slowest on laminin and tissue culture plastic. Basement membrane matrix proteins may promote intestinal epithelial differentiation and inhibit proliferation compared with interstitial collagen I. 相似文献
69.
In Vivo and In Vitro Evidence for the Biosynthesis of Testosterone in the Telencephalon of the Female Frog 总被引:5,自引:2,他引:3
Ayikoe G. Mensah-Nyagan Jean-Luc Do-Rego Marc Feuilloley Albert Marcual Catherine Lange †Georges Pelletier Hubert Vaudry 《Journal of neurochemistry》1996,67(1):413-422
Abstract: Neurons and glial cells are capable of synthesizing various steroid hormones, but biosynthesis of testosterone in the CNS has never been reported. The aim of the present study was to demonstrate the synthesis of testosterone in the frog brain. The presence of 17β-hydroxysteroid dehydrogenase (17β-HSD)-like immunoreactivity was detected in a population of glial cells located in the telencephalon. Reversed-phase HPLC analysis of brain tissue extracts combined with radioimmunoassay detection revealed the presence of substantial amounts of testosterone and 5α-dihydrotestosterone (5α-DHT) in the telencephalon where 17β-HSD-positive cells were visualized. In male frogs, castration totally suppressed testosterone and 5α-DHT in the blood and in the rhombencephalon but did not affect the concentration of these two steroids in the telencephalon. Chemical characterization of testosterone in female frog telencephalon extracts was performed by coupling HPLC analysis with gas chromatography-mass spectrometry. Using the pulse-chase technique with [3 H]pregnenolone as a precursor, the formation of a series of metabolites was observed, including dehydroepiandrosterone, androstenedione, testosterone, 5α-DHT, and estradiol. These data demonstrate the existence of an active form of 17β-HSD in the frog telencephalon, which is likely involved in testosterone biosynthesis within the brain. 相似文献
70.
Atmospheric CO2 concentration has increased by 25% over the preindustrial level. A parallel increase in C concentration and decreases in N
concentration and δ13C of plants grown throughout this century have been observed in plant specimens stored in herbaria. We tested our previous
results in a study of 12 more species collected in the western Mediterranean throughout this century (1920–1930, 1945–1955,
and 1985–1990) and tree rings of Quercus pubescens from the same area. These changes were accompanied by apparent increases in condensed tannin concentration. A decreasing trend
in δ15N both in herbarium material and tree rings was also found, indicating that ecosystems might cope with higher plant N demand
by decreasing N losses and increasing N fixation and mineralization. These results may contribute to a better understanding
of the effects of global change on carbon and nitrogen cycling.
Received: 12 November 1995 / Accepted: 17 May 1996 相似文献