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101.
102.
Kinetics of thin filament activation probed by fluorescence of N-((2-(Iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1, 3-diazole-labeled troponin I incorporated into skinned fibers of rabbit psoas muscle: implications for regulation of muscle contraction 总被引:2,自引:0,他引:2 下载免费PDF全文
Making use of troponin with fluorescently labeled troponin I subunit (N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1, 3-diazole-troponin I, IANBD-TnI) that had previously been described in solution studies as a probe for thin filament activation (. Proc. Natl. Acad. Sci. 77:7209-7213), we present a new approach that allows the kinetics of thin filament activation to be studied in skinned muscle fibers. After the exchange of native troponin for fluorescently labeled troponin, the fluorescence intensity is sensitive to both changes in calcium concentration and actin attachment of cross-bridges in their strong binding states (. Biophys. J. 77:000-000). Imposing rapid changes in the fraction of strongly attached cross-bridges, e.g., by switching from isometric contraction to high-speed shortening, causes changes in thin filament activation at fixed Ca(2+) concentrations that can be followed by recording fluorescence intensity. Upon changing to high-speed shortening we observed small (<20%) changes in fluorescence that became faster at higher Ca(2+) concentrations. At all Ca(2+) concentrations, these changes are more than 10-fold faster than force redevelopment subsequent to the period of unloaded shortening. We interpret this as an indication that equilibration among different states of the thin filament is rapid and becomes faster as Ca(2+) is raised. Fast equilibration suggests that the rate constant of force redevelopment is not limited by changes in the activation level of thin filaments induced by the isotonic contraction before force redevelopment. Instead, our modeling shows that, in agreement with our previous proposal for the regulation of muscle contraction, a rapid and Ca(2+)-dependent equilibration among different states of the thin filament can fully account for the Ca(2+) dependence of force redevelopment and the fluorescence changes described in this study. 相似文献
103.
Analysis of growth and division often involves measurements made on cell populations, which tend to average data. The value
of single cell analysis needs to be appreciated, and models based on findings from single cells should be taken into greater
consideration in our understanding of the way in which cell size and division are co-ordinated. Examples are given of some
single cell analyses in mammalian cells, yeast and other microorganisms. There is also a short discussion on how far the results
are in accord with simple models. 相似文献
104.
Wunsch SA Muller-Delp J Delp MD 《American journal of physiology. Heart and circulatory physiology》2000,279(4):H1715-H1723
At the onset of dynamic exercise, muscle blood flow increases within 1-2 s. It has been postulated that local vasodilatory agents produced by the vascular endothelium or the muscle itself contribute to this response. We hypothesized that only vasodilators that act directly on the vascular smooth muscle could produce vasodilation of skeletal muscle arterioles in <2 s. To test this hypothesis, we determined the time course of the vasodilatory response of isolated skeletal muscle arterioles to direct application of potassium chloride, adenosine, acetylcholine, and sodium nitroprusside. Soleus and gastrocnemius muscles were dissected from the hindlimbs of male Sprague-Dawley rats. First-order arterioles (100-200 microm) were isolated, cannulated on micropipettes, and pressurized to 60 cmH(2)O in an organ bath. Vasodilatory agents were added directly to the bath, and diameter responses of the arterioles were recorded in real time on a videotape recorder. Frame-by-frame analysis of the diameter responses indicated that none of the vasodilator agents tested produced significant diameter increases in <4 s in either soleus or gastrocnemius muscle arterioles. These results indicate that, although these local vasodilators produce significant vasodilation of skeletal muscle resistance arterioles, these responses are not rapid enough (within 1-2 s) to contribute to the initiation of the exercise hyperemic response at the onset of dynamic exercise. 相似文献
105.
106.
Background
A new sequence independent bioinformatics approach allowing genome-wide search for proteins with similar three dimensional structures has been developed. By utilizing the numerical output of the sequence threading it establishes putative non-obvious structural similarities between proteins. When applied to the testing set of proteins with known three dimensional structures the developed approach was able to recognize structurally similar proteins with high accuracy.Results
The method has been developed to identify pathogenic proteins with low sequence identity and high structural similarity to host analogues. Such protein structure relationships would be hypothesized to arise through convergent evolution or through ancient horizontal gene transfer events, now undetectable using current sequence alignment techniques. The pathogen proteins, which could mimic or interfere with host activities, would represent candidate virulence factors.The developed approach utilizes the numerical outputs from the sequence-structure threading. It identifies the potential structural similarity between a pair of proteins by correlating the threading scores of the corresponding two primary sequences against the library of the standard folds. This approach allowed up to 64% sensitivity and 99.9% specificity in distinguishing protein pairs with high structural similarity.Conclusion
Preliminary results obtained by comparison of the genomes of Homo sapiens and several strains of Chlamydia trachomatis have demonstrated the potential usefulness of the method in the identification of bacterial proteins with known or potential roles in virulence.107.
Inference for imputation estimators 总被引:16,自引:0,他引:16
108.
Efficient estimation of the prevalence of multiple rare traits 总被引:1,自引:0,他引:1
109.
It has been hypothesized that microgravity-induced orthostatic hypotension may result from an exaggerated vasodilatory responsiveness of arteries. The purpose of this study was to determine whether skeletal muscle arterioles exhibit enhanced vasodilation in rats after 2 wk of hindlimb unloading (HU). First-order arterioles isolated from soleus and white gastrocnemius muscles were tested in vitro for vasodilatory responses to isoproterenol (Iso), adenosine (Ado), and sodium nitroprusside (SNP). HU had no effect on responses induced by Iso but diminished maximal vasodilation to Ado and SNP in both muscles. In addition, vasodilatory responses in arterioles from control rats varied between muscle types. Maximal dilations induced by Iso (soleus: 42 +/- 6%; white gastrocnemius: 60 +/- 7%) and Ado (soleus: 51 +/- 8%; white gastrocnemius: 81 +/- 6%) were greater in arterioles from white gastrocnemius muscles. These data do not support the hypothesis that microgravity-induced orthostatic hypotension results from an enhanced vasodilatory responsiveness of skeletal muscle arterioles. Furthermore, the data support the concept that dilatory responsiveness of arterioles varies in muscle composed of different fiber types. 相似文献
110.