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1.
Bioaccessibility measurements have the potential to improve the accuracy of risk assessments and reduce the potential costs of remediation when they reveal that the solubility of chemicals in a matrix (e.g., soil) differs markedly from that in the critical toxicity study (i.e., the key study from which a toxicological or toxicity reference value is derived). We aimed to apply this approach to a brownfield site contaminated with chromium, and found that the speciation was CrIII, using a combination of alkaline digestion/diphenylcarbazide complexation and X-ray absorption near edge structure analysis. The bioaccessibility of Cr2O3, the compound on which a reference dose for CrIII is based, was substantially lower (<0.1%) than that of the CrIII in the soils, which was a maximum of 9%, giving relative bioaccessibility values of 13,000% in soil. This shows that the reference dose is based on essentially an insoluble compound, and thus we suggest that other compounds be considered for toxicity testing and derivation of reference dose. Two possibilities are CrCl3·6H2O and KCr(SO4)2·12H2O, which have been used for derivation of ecological toxicity reference values and are soluble at a range of dosing levels in our bioaccessibility tests. 相似文献
2.
Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium 总被引:13,自引:9,他引:4
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Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel. 相似文献
3.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
4.
5.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
6.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
7.
8.
9.
R A Kloner K A Reimer J T Willerson R B Jennings 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1976,151(4):677-683
Hypertonic mannitol previously has been shown to improve cardiac function, increase collateral flow, and decrease epicardial ST segment elevation following coronary occlusion in anesthetized or awake dogs. The present study quantitates by morphologic techniques, the effect of hypertonic mannitol on infarct size. Ischemic injury was produced by proximal occlusion of the circumflex artery for 40 min and necrosis was assessed after 48 hr of reflow. One group of dogs was given isotonic saline and the other hypertonic mannitol beginning the infusions just prior to, during, and for a short period after the release of the circumflex coronary artery occlusion. Serum osmolality increased by approximately 40 mOsm in the mannitol group. The administration of hypertonic mannitol was associated with a 40-50% reduction in infarct size ventricular fibrillation during occlusion and following release of the circumflex coronary artery occlusion was greater in mannitol-treated dogs although the difference was not statistically significant. Thus, the data obtained in this study extend previous observations and provide direct evidence that hypertonic mannitol can reduce infarct size in dogs with temporary circumflex artery occlusion and reflow. 相似文献
10.
E W Ades D J Phillips S L Shore D S Gordon M G LaVia C M Black C B Reimer 《Journal of immunology (Baltimore, Md. : 1950)》1976,117(6):2119-2123
Fluorescein-conjugated staphylococcal protein A (SPA) was complexed with either: 1) heat-aggregated IgG, 2) B cell specific antibody, or 3) T cell specific antibody and then used for an immunofluorescent analysis of mononuclear cell surfaces. Cellular Fc receptors failed to recognize the Fc region of aggregated IgG that had been blocked by SPA. Moreover, fluoresceinated SPA that had been complexed either with anti-Fab (B-cell specific) or T cell-specific antisera prevented the nonspecific binding of these reagents to the IgG-Fc receptors on mononuclear cells, thereby permitting the latter to be properly identified as B or T lymphocytes. In addition, when unconjugated SPA was added to presensitized target cells in a test for antibody-dependent cell-mediated cytotoxicity, cytolysis was abrogated. 相似文献