排序方式: 共有8条查询结果,搜索用时 15 毫秒
1
1.
Clustering of neurotransmitter receptors in the postsynaptic membrane is critical for efficient synaptic transmission. During
neuromuscular synaptogenesis, clustering of acetylcholine receptors (AChRs) is an early sign of postsynaptic differentiation.
Recent studies have revealed that the earliest AChR clusters can form in the muscle independent of motorneurons. Neurally
released agrin, acting through the muscle-specific kinase MuSK and rapsyn, then causes further clustering and localization
of clusters underneath the nerve terminal. AChRs themselves are required for agrin-induced clustering of several postsynaptic
proteins, most notably rapsyn. Once formed, AChR clusters are stabilized by several tyrosine kinases and by components of
the dystrophin/utrophin glycoprotein complex, some of which also direct postnatal synaptic maturation such as formation of
postjunctional folds. This review summarizes these recent results about AChR clustering, which indicate that early clustering
can occur in the absence of nerves, that AChRs play an active role in the clustering process and that partly different mechanisms
direct formation versus stabilization of AChR clusters.
Received 10 April 2002; received after revision 4 June 2002; accepted 10 June 2002 相似文献
2.
Nanostructures are of great interest not only for their basic scientific richness, but also because they have the potential to revolutionize critical technologies. The miniaturization of electronic devices over the past century has profoundly affected human communication, computation, manufacturing and transportation systems. True molecular-scale electronic devices are now emerging that set the stage for future integrated nanoelectronics. Recently, there have been dramatic parallel advances in the miniaturization of mechanical and electromechanical devices. Commercial microelectromechanical systems now reach the submillimetre to micrometre size scale, and there is intense interest in the creation of next-generation synthetic nanometre-scale electromechanical systems. We report on the construction and successful operation of a fully synthetic nanoscale electromechanical actuator incorporating a rotatable metal plate, with a multi-walled carbon nanotube serving as the key motion-enabling element. 相似文献
3.
4.
Phytotoxic effects of cadmium in leaf segments ofAvena sativa L., and the protective role of calcium
Cellular and Molecular Life Sciences - It is shown that ethylene production can be stimulated in peeled oat leaf segments in the dark by cadmiun at concentrations below 0.01 mM, and that... 相似文献
5.
The most common approach to combining forecasts at different levels of aggregation has been to sum (or average) the more disaggregated forecast, and take a weighted average of the aggregate forecasts. This paper develops a simple method for obtaining minimum variance pooled forecasts at the disaggregated level. The major advantage that this method has over the common approach is that it provides pooled forecasts at both the aggregated and disaggregated level. As will be shown, the resulting aggregate pooled forecast is identical to the forecast which would be obtained by simply pooling two forecasts at the aggregate level, while the disaggregated forecast maintains the aggregation identity required by the problem. 相似文献
6.
Energy spectra of quantum rings. 总被引:1,自引:0,他引:1
Quantum mechanical experiments in ring geometries have long fascinated physicists. Open rings connected to leads, for example, allow the observation of the Aharonov-Bohm effect, one of the best examples of quantum mechanical phase coherence. The phase coherence of electrons travelling through a quantum dot embedded in one arm of an open ring has also been demonstrated. The energy spectra of closed rings have only recently been studied by optical spectroscopy. The prediction that they allow persistent current has been explored in various experiments. Here we report magnetotransport experiments on closed rings in the Coulomb blockade regime. Our experiments show that a microscopic understanding of energy levels, so far limited to few-electron quantum dots, can be extended to a many-electron system. A semiclassical interpretation of our results indicates that electron motion in the rings is governed by regular rather than chaotic motion, an unexplored regime in many-electron quantum dots. This opens a way to experiments where even more complex structures can be investigated at a quantum mechanical level. 相似文献
7.
Summary It is demonstrated that the uptake of nitrogen dioxide (NO2) byPhaseolus vulgaris L. is decreased by the addition of sodium chloride (NaCl) to the root medium, as a result of increased diffusive resistance of the leaves. The NO2-uptake rate constant measured kinetically was in agreement with the nitrite content of the leaves after the fumigation. 相似文献
8.
Nicotinic acetylcholine receptors (nAChRs) exist in many subtypes and are found in the peripheral and central nervous system
where they mediate or modulate synaptic transmission. We review how tyrosine phosphorylation and kinases regulate muscle and
neuronal nAChRs. Interestingly, although some of the same kinase players interact with the various receptor subtypes, the
functional consequences are different. While concerted action of MuSK, Abl- and Src-family kinases (SFKs) regulates the synaptic
distribution of nAChRs at the neuromuscular junction, SFKs activate heteromeric neuronal nAChRs in adrenal chromaffin cells,
thereby enhancing catecholamine secretion. In contrast, the activity of homomeric neuronal nAChRs, as found in the hippocampus,
is negatively regulated by tyrosine phosphorylation and SFKs. It appears that tyrosine kinases provide the means to regulate
all nAChRs; but the functional consequences, even those caused by the same kinase family, are specific for each receptor subtype
and location.
Received 21 February 2006; received after revision 24 July 2006; accepted 30 August 2006 相似文献
1