首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 860 毫秒
1.
The aim of this study was to evaluate the effect of magnesium (Mg) loading (10.0 mg Mg/kg body wt) and daily Mg supplements (5.0 mg Mg/kg body wt) on Mg deficiency shown by increased and not by decreased serum Mg concentration during hypokinesia (decreased km number/d). The studies were done during 30 d of prehypokinesia and 364 d of hypokinesia (HK) periods. Forty endurance-trained volunteers aged 22–26 yr with a peak VO2 max of 66.3 mL·kg−1 min−1 and with an average 15.0 km/d running distance were chose as subjects. They were equally divided into four groups:
1.  Unsupplemented ambulatory control subjects (UACS).
2.  Unsupplemented hypokinetic subjects (UHKS).
3.  Supplemented hypokinetic subjects (SHKS).
4.  Supplemented ambulatory control subjects (SACS).
The SHKS and SACS groups took daily 5.0 mg elemental Mg/kg body wt and subjected to Mg loading (10.0 mg Mg/kg body wt). Both the SHKS and UHKS groups were maintained under an average running distance of 4.7 km/d, whereas the SACS and UACS groups did not experience any modifications to their normal training routines and diets. During the prehypokinetic and hypokinetic periods, excretion of Mg in feces and urine, concentration of Mg in serum, and Mg balance were measured. urinary and serum sodium (Na), potassium (K), and calcium (Ca) were also determined. In both SHKS and UHKS groups, fecal Mg loss, urinary excretion of electrolytes, and serum concentrations of electrolytes increased significantly (p≤0.05) when compared with the SACS and UACS groups. During Mg loading tests, urinary and fecal Mg excretion was also greater in the SHKS and UHKS groups than in the SACS and UACS groups. Throughout the study, Mg balance was negative in the SHKS and UHKS groups, whereas in the SACS and UACS groups, Mg balance was positive. It was concluded that significant losses of Mg occurred in the presence of negative Mg balance and Mg deficiency in endurance-trained subjects during prolonged exposure to HK, daily mg supplements, and Mg loading tests. This suggests that Mg is not entering or being retaining by the bones and cells of many tissues where most Mg is deposited normally, resulting in Mg deficiency as was shown by the increased serum Mg concentration.  相似文献   

2.
In order to study the metabolism of mercury (Hg), its affinity to metallothionein (MT), and its influence on levels of the essential metals copper and zinc in the brain tissue of rats exposed to elemental mercury (HgO) vapor was investigated. The major findings were:
1.  After long-term exposure, about 40% of mercury was found in the brain water-soluble phase (supernatant);
2.  In brain supernatant, about 80% of Hg was found in the range of low-molecular-weight proteins; the MT-like protein Hg−Cu−Zn-thionein was isolated and partially characterized;
3.  HgO vapor exposure resulted in increased tissue levels of essential Cu and Zn in addition to exogenous Hg; and
4.  Experiments showed that HgO vapor exposure can induce the stimulation of rat brain MT synthesis.
A part of this investigation was reported at TEMA 7, Dubrovnik, May 20–25, 1990 (Falnoga et al 1991).  相似文献   

3.
1.  Coupling mechanisms between ciliary beating and the membrane potential in Paramecium were investigated under voltage clamp applying intracellular pressure injection of cAMP, cGMP and Ca-EGTA buffer. Ciliary responses following step changes in membrane potential were recorded by high-speed video on magnetic tape.
2.  Injections of cAMP and cGMP up to millimolar concentrations caused no detectable changes in the frequency voltage relationship. A minor effect was that the ciliary reorientation towards the anterior cell end (reversal) tended to be inhibited with depolarization up to 10 mV.
3.  Injection of Ca2+ into the cell clamped at the resting potential caused a transient anteriad ciliary reorientation and a simultaneous increase in the beating frequency.
4.  Injection of EGTA (to buffer Ca2+ below 10–8 M) was ineffective in relation to frequency for several minutes. After this time, hyperpolarization- and depolarization activated frequency responses of EGTA-injected cells were increasingly inhibited. The ciliary reorientation following depolarization was not affected by EGTA.
5.  A posterior contraction of the cell diameter was noticed upon membrane hyperpolarization. The contraction coincided in time with the increase in beating frequency.
6.  The results support the view that the voltage-dependent augmentation of the ciliary beating rate is not directly mediated by an intracellular increase in either cAMP or cGMP.
7.  The role of Ca2+ as intracellular messenger in the ciliary and somatic compartments is discussed.
  相似文献   

4.
G. Rombi  G. Piu  S. Piro  V. Anedda 《Cytotechnology》1993,11(Z1):S147-S149
Being able to carry zidovudine (AZT) at known concentrations into CD4+/CD38+ and CD14+ cells permits:
–  - to reduce the drug dosage and to increase the interval for administration (until 1 dose I.V. every week);
–  - to modulate the drug concentration into the CD4+/CD38 an CD14+ cells in relation to the in vitro determined HIV sensitiveness;
–  - to eliminate haematological, medullary and general toxicity;
–  - to be able to treat severely hill patients.
Further studies are necessary in order to:
–  - To find out the better phase to start the therapy;
–  - To use several drugs with different mechanisms of action in order to slow down as much as possible the presence of resistant viral strains.
–  - As for other drugs which are beginning to be used with artificial vehicles, futher studies are required to improve the selectivity and safety of LIPOAZT for the target cells including macrophages.
  相似文献   

5.
1.  Properties of the membrane currents ofDidinium nasutum have been investigated under voltage clamp in different solutions and after deciliation.
2.  Theearly transient Ca2+ inward current activates in a voltage-dependent manner. Inactivation is both Ca2+ -dependent and voltage-dependent.
3.  Alate Ca2+ current rises with time to peak > 50 ms and decays in the order of seconds.
4.  Activation and inactivation of the late Ca2+ current is voltage-dependent.
5.  The delayed outward current is activated by voltage. The kinetics of this K+ current, but not its amplitude, are enhanced in the presence of intracellular EGTA.
6.  The two voltage-dependent Ca2+ channels are located in the cilia, whereas all K+ channels are restricted to the somatic membrane.
  相似文献   

6.
Müller  D. G.  Frenzer  K. 《Hydrobiologia》1993,(1):37-44
Culture studies with healthy and virus-infected isolates of Ectocarpus siliculosus, Feldmannia simplex and F. irregularis gave the following results:
–  Virus particles are produced in deformed reproductive organs (sporangia or gametangia) of the hosts and are released into the surrounding seawater.
–  Their infective potential is lost after several days of storage under laboratory conditions.
–  New infections occur when gametes or spores of the host get in contact with virus particles. The virus genome enters all cells of the developing new plant via mitosis.
–  Virus expression is variable, and in many cases the viability of the host is not impaired. Infected host plants may be partly fertile and pass the infection to their daughter plants.
–  Meiosis of the host can eliminate the virus genome and generate healthy progeny.
–  The genome of the Ectocarpus virus consists of dsDNA. Meiotic segregation patterns suggest an intimate association between virus genome and host chromosomes.
–  An extra-generic host range has been demonstrated for the Ectocarpus virus.
–  Field observations suggest that virus infections in ectocarpalean algae occur on all coasts of the world, and many or all Ectocarpus and Feldmannia populations are subject to contact with virus genomes.
  相似文献   

7.
Twelve of the main European LCA software packages currently available are examined wirh the aim of establishing which are the most appropriate for LCAs on industrial processes. The packages performances are assessed in terms of
–  • Volume of Data
–  • WindowsTM environment
–  • Network Capabilities
–  • Impact Assessment
–  • Graphical representation of the inventory results
–  • Sensitivity analysis
–  • Units
–  • Cost
–  • User Support
–  • Flow Diagrams
–  • Burdens allocation
–  • Transparency of data
–  • Input & output parameters
–  • Demo version
–  • Quality of data
The review concludes with a Specification Table which summarises the facilities available on each software package. The general conclusion from this study is that for industrially based LCAs, there are four packages which may offer advantages over the rest. These are The Boustead Model, The Ecobilan Group’s TEAM™, PEMS 3.0 and SimaPro 3.1.  相似文献   

8.
J. Robb 《Human Evolution》1994,9(3):215-229
In recent years anthropologists have made much progress in understanding ancient activities from skeletal remains. In this paper, material from the Iron Age cemetery at Pontecagnano (VII-IV century BC) is used to illustrate activity-related traits of eight basic categories:
(1)  idiosyncratic patterns of dental wear
(2)  activity-related articular degeneration
(3)  non-pathological functional alterations (neoformations, contact facets)
(4)  mechanical remodelling of bone architecture
(5)  enthesopathies (muscular lesions)
(6)  traumatic lesions
(7)  activity-related pathologies
(8)  activity-related nutritional characteristics
These traits, and others, can be used not only singly but in conjunction to define (a) patterns of activity and occupational specialization for individuals, and (b) distributions within society reflecting the basic division of labor by geneder and class.  相似文献   

9.
1.  We used laser vibrometry and free field sound stimulation to study the frequency responses of the eardrum and the lateral body wall of awake male Eleutherodactylus coqui.
2.  The eardrum snowed one of two distinct frequency responses depending on whether the glottis was open (GO response) or closed (GC response) during the measurement.
3.  The lateral body wall vibrated with a maximum amplitude close to that of the eardrum and in the same frequency range.
4.  Covering the frog's body wall with vaseline reduced the vibration amplitude of the GC response by up to 15 dB.
5.  When a closed sound delivery system was used to stimulate a local area of the body wall the eardrum also showed one of two types of responses.
6.  These results suggest that sound is transmitted via the lung cavity to the internal surface of the eardrum. This lung input has a significant influence on the vibrations of the eardrum even when the glottis is closed.
7.  The vibration amplitude of the eardrum changed with the angle of sound incidence. The directionality was most pronounced in a narrow frequency range between the two main frequencies of the conspecific advertisement call.
  相似文献   

10.
Thiolutin was found to inhibit the utilization of glucose and other growth substrates in Escherichia coli. The inhibition was detected by a sharp drop of the respiration rate after addition of the antibiotic. The actual function affected was allocated to the cytoplasmic membrane of the bacterial cells by the following evidence:
–  - spheroplasts were affected like intact cells,
–  - individual reactions of either the electron transport chain or the glycolytic pathway were not inhibited,
–  - glucose consumption in the culture stopped and the cells accumulated guanosine tetraphosphate as under starvation conditions,
–  - activation of the cell's apo-glucose dehydrogenase restored respiration via bypassing the glucose phosphotransferase system.
It was concluded that the transport of certain substrates across the membrane was inhibited.  相似文献   

11.
1.  A retention time of 150 days in the storage reservoir leads to a quite considerable reduction in copper and lead concentration (around 75% for lead and 50% for copper), while a levelling-off in the marked variations in the water flowing in is also found.
2.  Copper concentrations in the storage reservoir and the model reservoirs show a less constant picture with time then lead concentrations. This may well be caused by the absorption of copper by e.g. phytoplankton.
3.  Treatment of the water with Fe++ or AVR seems to have no effect on the removal of lead or suspended matter.
4.  Because of the small number of measurements it is difficult to quantify these results.
5.  For statements about seasonal trends, measurements must be made over a period of at least three years; they must be made at least once a week and the sampling procedure as regards place and frequency must remain unchanged.
6.  The available data indicate that in spite of the effect of mobilisation the removal of the two metals is such that sudden drastic rises of concentration in the unfiltered surface water entering the purification installation is not to be expected.
  相似文献   

12.
In this report we describe the most suitable protocol for callus formation and plant regeneration for cotton. We screened 15 cotton (Gossypium hirsutum L.) genotypes for metal resistance and two of them, Nazilli M-503 (M503) Nazilli 143 (N-143) selected as Cd, Cu and Ni resistant. The cotyledonary nodes from these genotypes were the best explants for regeneration of shoots (more than 90 %) and roots (50 to 70 %). Shoot apex also gave good shoot regeneration (more than 90 %) but their root regeneration efficiency was low (35 %). These results show that Murashige and Skoog (MS) media containing 0.44 μM naphthaleneacetic acid (NAA) and 0.98 μM indole-3-butyric acid (IBA) was the most suitable recipe for getting high shoot and root regeneration from cotyledonary nodes of N-143 and M503 cotton genotypes.Abbreviations
2,4 D  2,4-dichlorophenoxyacetic acid
BAP  6-benzylaminopurine
GA  gibberellic acid
IBA  indole-3-butyric acid
MS medium  Murashige and Skoog medium
NAA  naphthaleneacetic acid
This work was supported by the Textile Industry grant No. F000301 given to A.R. Memon.  相似文献   

13.
1.  Under laboratory conditions complete development of H. sparsutum is shown within a temperature range of-0.7°C to +8°C. Constant temperatures above 10°C are lethal to the population. Larval growth (L1 to L5) is strictly temperature-dependent between-0.7 and +3.5°C, but slightly temperature compensated between +3.5 and +8°C.
2.  Rate of egg production is highest at an average daily temperature of-0.7°C.
3.  The sixth larval stage (L6) can be subdivided into a wandering and feeding period of about 40 days (at 7.3°C) and a following prepupal resting stage (PPR) with a high variability in duration, even at one and the same temperature, which ends with pupation.
4.  Entrance into this resting stage seems to be independent of environmental changes and can occur at every time of the year. Termination of the PPR depends upon light stimuli received during the entire larval period.
5.  Readiness for pupation exists when the photoperiod in the PPR exceeds that during hatching of first larva. A decreasing photoperiod during PPR triggers pupation in prepupae of various age.
6.  The diapause stage seems to be a primary factor synchronizing the life cycle with seasonal changes in the environment.
  相似文献   

14.
Glycolytic intermediates and related metabolites were measured in the fat body of the American cockroach (Periplaneta americana) to locate the rate-limiting reactions that regulate glycolysis during the action of the corpus cardiacum (CC) in vitro.
1.  The concentrations of glucose 1-phosphate, fructose 6-phosphate, and fructose 1,6-bisphosphate were approximately doubled after 30 min treatment with CC extract, whereas that of glucose 6-phosphate increased more than four-fold. Slightly lower increases occurred after 10 and 60 min treatment.
2.  Triose phosphates, 2-phosphoglyceric acid, phosphoenolpyruvate and pyruvate were unaffected by CC extract.
3.  Glycerol 3-phosphate, which is 20\2-200 times more concentrated than any of the other measured metabolites in the unstimulated tissue, is increased more than two-fold by CC extract.
4.  NAD, NADP, and ATP were not significantly affected by CC extract. ADP was increased significantly by the gland extract.
  相似文献   

15.
3DFS is a 3D flexible searching system for lead discovery. Version 1.0 of 3DFS was published recently (Wang, T.; Zhou, J. J. Chem. Inf. Comput. Sci., 1998, 38, 71–77). Here version 1.2 represents a substantial improvement over version 1.0. There are six major changes in version 1.2 compared to version 1.0.
1.  A new rule of aromatic ring recognition.
2.  The inclusion of multiple-type atoms and chains in queries.
3.  The inclusion of more spatial constraints, especially the directions of lone pairs.
4.  The improvement of the query file format.
5.  The addition of genetic search for flexible search.
6.  An output option for generating MOLfiles of hits.
Besides the above, this paper supplies:
1.  More query examples.
2.  A comparison between genetic search and Powell optimization.
3.  More detailed comparison between 3DFS and Chem-X.
4.  A preliminary application of 3DFS to K+ channel opener studies.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s0089490050231  相似文献   

16.
Conclusions  
(1)  The aminoesters inhibit glucose-stimulated proton extrusion by yeast cells.
(2)  The inhibitory activity depends on aliphatic carbon chain length.
(3)  The inhibition of proton extrusion is concentration-dependent.
(4)  The aminoesters stimulate quinacrine accumulation in vacuoles of yeast cells so they should possess affinities for lysosomes.
This work was supported byKBN grant no. 7 A203 013 07.  相似文献   

17.
1.  The effects of three barbiturates and the local anesthetic procaine on the ion channel function of mouse nicotinic acetylcholine receptor (nAChR) muscle subtype expressed inXenopus laevis oocytes were examined by whole-cell voltage-clamp technique.
2.  A concentration-response curve for the specific nicotinic agonist dimethylphenylpiperazinium iodide (DMPP) was first determined. This agonist produced increasing whole-cell currents up to a concentration of 100µM (EC50 = 13µM), then decreased responses at higher concentrations.
3.  The barbiturates (amobarbital, secobarbital, pentobarbital) and procaine produced reversible inhibition of DMPP-induced currents at clinically used concentrations. The two classes of drugs differed in the voltage dependence of the inhibition: procaine-induced inhibition was increased at more negative transmembrane holding potentials (-90 vs. -45 mV); whereas amobarbital-induced inhibition did not vary at different transmembrane potentials.
4.  Mutant forms of the nAChR, containing single amino acid changes in the M2 regions of and subunits, showed increased sensitivity to procaine but no change in sensitivity to amobarbital-induced inhibition.
5.  These electrophysiologic studies provide further evidence that barbiturates and local anesthetics produce inhibition of the nAChR at different sites.
  相似文献   

18.
1.  We have obtained a cDNA clone encoding a human retinal D2 dopamine receptor.
2.  The longest open reading frame (1242 bp) of this clone encodes a protein of 414 amino acids having a predicted molecular weight of 47,000 and a transmembrane topology similar to that of other G protein-coupled receptors.
3.  Transient transfection of COS-7 cells with an expression vector containing the clone resulted in expression of a protein possessing a pharmacological profile similar to that of the D2 dopamine receptor found in striatum and retina.
4.  Northern blot analysis indicated that, in rat brain and retina, the mRNA for this receptor was 2.9 kb in size.
5.  In situ hybridization was performed to examine the distribution of the mRNA for this receptor in human retina. Specific hybridization was detected in both the inner and the outer nuclear layers.
6.  These findings are consistent with prior physiological and autoradiographic studies describing the localization of D2 dopamine receptors in vertebrate retinas. Our observations suggest that photoreceptors as well as cells in the inner nuclear layer of human retinas may express the mRNA for this D2 dopamine receptor.
  相似文献   

19.
1.  The overall rate of feeding at 28°C bears an inverse relationship to size; the time course of feeding appears to be size-independent and shows a decline with increase in time.
2.  Absorption efficiency is independent of size.
3.  The rates of absorption and conversion and conversion efficiency are inversely related to size.
4.  The rate of feeding is reflected on the rates of absorption and conversion.
  相似文献   

20.
1.  A 28-kDa peptide from the brain of the tobacco hornworm,Manduca sexta, was purifiedvia HPLC. The peptide copurified with the insect neurohormone, prothoracicotropic hormone (PTTH), through two HPLC columns.
2.  Immunocyctochemistry using polyclonal antibodies against the 28-kDa peptide revealed that the peptide was produced in the same protocerebral neurons that produce PTTH. Western blot analysis demonstrated that the 28-kDa peptide and big PTTH are different molecules.
3.  A PTTHin vitro bioassay indicated that despite having chromatographic properties similar to those of big PTTH and being produced by the same neurons, the 28-kDa peptide did not have PTTH activity.
4.  Amino acid sequence analysis yielded a 27 N-terminal amino acid sequence that had no similarity with known peptides.
5.  Immunocytochemical studies revealed that the 28-kDa peptide is present as early as 30% embryonic development and is absent by adult eclosion. This is in contrast to big PTTH, which is expressed throughout theManduca life cycle.
6.  These data suggest that the 28-kDa peptide is another secretory phenotype of the lateral neurosecretory cell group III (L-NSC III) which may have functions distinct from those for big PTTH or may act synergistically with big PTTH.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号