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31.
The Ehrlich ascites tumor cell has been used as a model of an unspecialized mammalian cell, in an attempt to disclose the mechanisms involved in the regulation of cellular water and salt content. In hypotonic medium Ehrlich cells initially swell as nearly perfect osmometers, but subsequently recover their volume within about 10 min with an associated net loss of KCl, amino acids, taurine and cell water. The net loss of KCl takes place mainly via separate, conductive K+ and Cl- transport pathways, and the net loss of taurine through a passive leak pathway. Ca2+ and calmodulin appear to be involved in the activation of the K+ and Cl- channels, as well as the taurine leak pathway. In hypertonic medium Ehrlich cells initially shrink as osmometers, but subsequently recover their volume with an associated net uptake of KCl and water. In this case, the net uptake of KCl is the result of the activation of an electroneutral, Na+- and Cl- -dependent cotransport system with subsequent replacement of cellular Na+ by extracellular K+ via the Na+/K+ pump. In the present review we describe the ion and taurine transporting systems which have been identified in the plasma membrane of the Ehrlich ascites tumor cell. We have emphasized the selectivity of these transport pathways and their activation mechanisms. Finally, we propose a model for the activation of the conductive K+ and Cl- transport pathways in Ehrlich cells which includes Ca2+, leukotrienes, and inositol phosphate as intracellular second messengers. 相似文献
32.
Urs Boutellier Ramon Büchel Andreas Kundert Christina Spengler 《European journal of applied physiology and occupational physiology》1992,65(4):347-353
Recently, we have shown that an untrained respiratory system does limit the endurance of submaximal exercise (64% peak oxygen consumption) in normal sedentary subjects. These subjects were able to increase breathing endurance by almost 300% and cycle endurance by 50% after isolated respiratory training. The aim of the present study was to find out if normal, endurance trained subjects would also benefit from respiratory training. Breathing and cycle endurance as well as maximal oxygen consumption (VO2max) and anaerobic threshold were measured in eight subjects. Subsequently, the subjects trained their respiratory muscles for 4 weeks by breathing 85-160 l.min-1 for 30 min daily. Otherwise they continued their habitual endurance training. After respiratory training, the performance tests made at the beginning of the study were repeated. Respiratory training increased breathing endurance from 6.1 (SD 1.8) min to about 40 min. Cycle endurance at the anaerobic threshold [77 (SD 6) %VO2max] was improved from 22.8 (SD 8.3) min to 31.5 (SD 12.6) min while VO2max and the anaerobic threshold remained essentially the same. Therefore, the endurance of respiratory muscles can be improved remarkably even in trained subjects. Respiratory muscle fatigue induced hyperventilation which limited cycle performance at the anaerobic threshold. After respiratory training, minute ventilation for a given exercise intensity was reduced and cycle performance at the anaerobic threshold was prolonged. These results would indicate the respiratory system to be an exercise limiting factor in normal, endurance trained subjects. 相似文献
33.
Characterization and localization of cis-diamminedichloro-platinum(II) adducts on a purified oligonucleotide containing the codons 12 and 13 of H-ras proto-oncogene. 下载免费PDF全文
M J Pillaire G Villani J S Hoffmann A M Mazard M Defais 《Nucleic acids research》1992,20(24):6473-6479
The use of substrates containing well defined adducts at precise sites, is required to perform a careful analysis of the toxic and mutagenic potential of a lesion. As a first step in this direction the octamer 5'-d(CCGGCGGT), containing the sequence of the codons 12 d(GGC) and 13 d(GGT) of the human H-ras gene, was reacted with the antitumoral drug cis-diamminedichloroplatinum(II). The platinated products have been purified by HPLC. A first set of experiments, including enzymatic digestions with nuclease P1 followed by alkaline phosphatase and acid-catalysed hydrolysis, allowed us to determine which bases were engaged in the cis-DDP lesions. Our results indicate that only guanine residues were chelated with cisplatin to yield bifunctional adducts. Furthermore, by performing enzymatic digestions with phosphodiesterases, we have located the adducts with respect to the 5' end of the octamer. Among the purified and characterized platinated oligonucleotides, three present a particular interest, since we have shown here that the cis-d(GpG) adduct is precisely situated either at the d(GGC) or at the d(GGT) or at both sites of their sequence. 相似文献
34.
35.
Christina Lyra Harri Savilahti Dennis H. Bamford 《Molecular & general genetics : MGG》1991,228(1-2):65-69
Summary Using electroporation with the phage PRD1 genome, we set up a high-frequency DNA transfer system for a linear dsDNA molecule with 5-covalently linked terminal proteins. The transfer was saturated when more than 100 ng of PRD1 genome was used. Electroporation efficiency was about four orders of magnitude higher than that obtained with transfection. Removal of the terminal protein abolished plaque formation, which could not be rescued by supplying the terminal protein or phage DNA polymerase or both in trans. 相似文献
36.
Authors studied an incidence of myocardial infarction in women, specially aged below 50 years. Infarct localisation, complications during the treatment, coronary disease risk factors and mortality were estimated. In the most young women with myocardial infarction 2-3 risk factors were found, simultaneously specially cigarette smoking--all studied women aged below 50 years smoked cigarettes. Hospital course of myocardial infarction was as a rule not complicated. Mortality in young and in all observed women was however twice higher in comparison to control group of males. 相似文献
37.
38.
M. Heinz R. Krattenmacher B. Hoffmann W. Clauss 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(4):363-370
Summary Transepithelial electrogenic Na+ transport (INa) was investigated in the coprodeum of 20-days-old chicken embryos in Ussing chambers. Short circuit current (Isc) and transepithelial resistance (Rt) were 14.7±4.8 A · cm-2 (n=12) and 0.53±0.09 k · cm-2 (n=12), respectively. INa was calculated from changes in Isc by substitution of mucosal Na+ by (N-methyl-d-glucamine) (NMDG). Isc inversed during Na+ removal, and INa was found to be 27.8±4.7 A · cm-2 (n=12). Amiloride (100 mol · l-1) inhibited only about 60% of INa. Analysis of Isc fluctuations revealed a Lorentzian component in the power density spectrum with a corner frequency of about 57 Hz. This component was not correlated to INa, and its origin is still unclear. Removal of mucosal Ca2+ increased INa about 2.5-fold due to an increase of the amiloride-insensitive component of INa in additionally investigated adult tissues. The results clearly show that this is due to a non-selective cation channel with an apparent order of selectivity Cs+>Na+=K+>Rb+>Li+. The Ca2+ concentration required to block 50% of the Isc was about 18 mol · l-1. The I
sc
Ca
could also be supressed by other divalent cations such as Mg2+ and Ba2+. Additionally, an INa-linked Lorentzian component occurred which dominated the control spectrum with a significantly higher corner frequency (about 88 Hz). The results indicate that Na+ absorption in the coprodeum of the chicken embryo is more complex than in adult hens. However, the Ca2+ sensitivity of INa is similar to comparable effects described for other epithelia. This possibly reflects the existence of two types of amiloride-insensitive apical cation channels as pathways for Na+ absorption, which may be involved to differing degrees in ontogenetic developments of nonselective channels to Na+-specific ion channels.Abbreviations
DPL
direct-linear-plot method
-
slope of the back-ground noise component
-
EGTA
ethylene glycol-bi(2-amino-ethylether)-N,N,N,N-tetraacetic acid
-
f
frequency
-
f
c
corner frequency of the Lorentzian noise component
-
G
t
transepithelial conductance
-
HEPES
N-hydroxyethylpiperazine-N-ethanesulfonic acid
-
I
sc
short-circuit current
-
I
Na
transepithelial sodium current
-
I
sc
Ca
Ca2+-sensitive short-circuit current
-
K
m
Ca
Michaelis-Menten constant for Ca2+
-
K
B
power density of the background noise component at f=1Hz
-
m
mucosal
-
NMDG
N-methyl-D-glucamine
-
R
t
transepithelial resistance
-
s
serosal
-
SEM
standard error of mean
-
S(f)
power density of the Lorentzian noise component
-
S
o
plateau value of the Lorentzian noise component 相似文献
39.
Identification of a fibroblast growth factor-binding protein in Drosophila melanogaster. 总被引:1,自引:0,他引:1 下载免费PDF全文
As assessed by competitive binding and protein-crosslinking experiments, Drosophila melanogaster cells possess basic fibroblast growth factor (bFGF)-specific binding proteins that are similar to FGF receptors on vertebrate cells in molecular weight and binding affinity; these D. melanogaster cells, however, have no detectable binding proteins for acidic fibroblast growth factor (aFGF). Consistent with the presence of bFGF-specific binding proteins, D. melanogaster cells degrade bFGF but not aFGF. These results indicate the conservation of heparin-binding growth factors and receptors between vertebrates and D. melanogaster. 相似文献
40.
Striking homology of the ''variable'' N-terminal as well as the ''conserved core'' domains of the mouse and human TATA-factors (TFIID). 总被引:18,自引:9,他引:9 下载免费PDF全文
T Tamura K Sumita I Fujino A Aoyama M Horikoshi A Hoffmann R G Roeder M Muramatsu K Mikoshiba 《Nucleic acids research》1991,19(14):3861-3865