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排序方式: 共有218条查询结果,搜索用时 15 毫秒
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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 下载免费PDF全文
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.
R McCarter J McGee S Witherspoon C J Gauntt A Vardiman 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1986,182(3):308-314
Isometric contractile properties of isolated phrenic nerve-diaphragm muscle preparations were used to study the effects of picornavirus infections on diaphragm muscle function. Properties of muscles from virus-inoculated and control mice were similar during brief contractions. However, when subjected to a series of fatiguing contractions by indirect or direct stimulation, muscles of mice inoculated with a paralytic variant of encephalomyocarditis (EMC) virus showed a greater rate of fatigue and a reduced capacity to recover from fatigue than did muscles from uninoculated control mice or muscles from mice inoculated with a nonparalytic coxsackievirus B3 (CVB3). Mice paralyzed by EMC virus infection had high titers of virus in the brain and similar titers of virus in diaphragm muscle as found in diaphragm muscles of CVB3-inoculated mice. The results indicate that EMC virus infection of mice leads to increased fatigability of the diaphragm muscle and that there are both neural and muscular components of this enhanced fatigue. 相似文献
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Maternal diabetes and cardiovascular malformations: predominance of double outlet right ventricle and truncus arteriosus 总被引:4,自引:0,他引:4
Most studies on the relationship of maternal diabetes to cardiovascular malformations (CVM) have been prospective investigations of pregnancy outcome and therefore could not identify associations with rare cardiac lesions. The results of a retrospective study shed new light on the risks of specific cardiac defects in diabetic pregnancies. The Baltimore-Washington Infant Study, a population-based case-control investigation of CVM, provides information on maternal diabetes reported in personal interviews. Among 2259 mothers of cases, 35 (1.5%) reported diabetes present before pregnancy (called "overt") and 95 (4.2%) reported diabetes only during pregnancy (called "gestational"). Among 2,801 mothers of controls, 14 (0.5%) had overt diabetes and 83 (3.0%) had gestational diabetes. Malformation-specific risks were expressed as odds ratios (OR) with 99.5% confidence intervals (CI). The strongest associations with overt maternal diabetes were found with double outlet right ventricle (OR 21.33; 99.5% CI 3.34, 136.26), and truncus arteriosus (OR 12.81; 99.5% CI 1.43, 114.64). No significant diagnosis-specific associations were found with gestational diabetes. Non-cardiac malformations were present in 23% of infants with CVM whose mothers had overt diabetes and in 26% of infants with CVM whose mother had gestational diabetes, in 32% of infants with CVM whose mothers did not have diabetes, and in 4% of controls. Double outlet right ventricle and truncus arteriosus are malformations dependent upon neural-crest-cell-derived ectomesenchymal tissues; these are precisely the conotruncal abnormalities that result from experimental ablation of the neural crest in chick embryos. The association with diabetes suggests a further etiologic link between these two lesions. 相似文献
6.
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
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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
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10.