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Elizabeth Storer Scholl Antonella Pirone Daniel H Cox R Keith Duncan Michele H Jacob 《Channels (Austin, Tex.)》2014,8(1):62-75
Small conductance Ca2+-sensitive potassium (SK2) channels are voltage-independent, Ca2+-activated ion channels that conduct potassium cations and thereby modulate the intrinsic excitability and synaptic transmission of neurons and sensory hair cells. In the cochlea, SK2 channels are functionally coupled to the highly Ca2+ permeant α9/10-nicotinic acetylcholine receptors (nAChRs) at olivocochlear postsynaptic sites. SK2 activation leads to outer hair cell hyperpolarization and frequency-selective suppression of afferent sound transmission. These inhibitory responses are essential for normal regulation of sound sensitivity, frequency selectivity, and suppression of background noise. However, little is known about the molecular interactions of these key functional channels. Here we show that SK2 channels co-precipitate with α9/10-nAChRs and with the actin-binding protein α-actinin-1. SK2 alternative splicing, resulting in a 3 amino acid insertion in the intracellular 3′ terminus, modulates these interactions. Further, relative abundance of the SK2 splice variants changes during developmental stages of synapse maturation in both the avian cochlea and the mammalian forebrain. Using heterologous cell expression to separately study the 2 distinct isoforms, we show that the variants differ in protein interactions and surface expression levels, and that Ca2+ and Ca2+-bound calmodulin differentially regulate their protein interactions. Our findings suggest that the SK2 isoforms may be distinctly modulated by activity-induced Ca2+ influx. Alternative splicing of SK2 may serve as a novel mechanism to differentially regulate the maturation and function of olivocochlear and neuronal synapses. 相似文献
3.
Plant chloroplasts are not only the main cellular location for storage of elemental iron (Fe), but also the main site for Fe, which is incorporated into chlorophyll, haem and the photosynthetic machinery. How plants measure internal Fe levels is unknown. We describe here a new Fe‐dependent response, a change in the period of the circadian clock. In Arabidopsis, the period lengthens when Fe becomes limiting, and gradually shortens as external Fe levels increase. Etiolated seedlings or light‐grown plants treated with plastid translation inhibitors do not respond to changes in Fe supply, pointing to developed chloroplasts as central hubs for circadian Fe sensing. Phytochrome‐deficient mutants maintain a short period even under Fe deficiency, stressing the role of early light signalling in coupling the clock to Fe responses. Further mutant and pharmacological analyses suggest that known players in plastid‐to‐nucleus signalling do not directly participate in Fe sensing. We propose that the sensor governing circadian Fe responses defines a new retrograde pathway that involves a plastid‐encoded protein that depends on phytochromes and the functional state of chloroplasts. 相似文献
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Comparison of intestine and bone marrow radiosensitivity of the BALB/c and the C57BL/6 mouse strains and their B6CF1 offspring 总被引:1,自引:0,他引:1
W R Hanson R J Fry A R Sallese H Frischer T Ahmad E J Ainsworth 《Radiation research》1987,110(3):340-352
The radiosensitivity as measured by LD50/6 or LD50/30 of the F1 hybrid B6CF1 (C57BL/6 X BALB/c) is similar to that of C57BL/6 mice but markedly different from BALB/c. The LD50/6 for BALB/c mice was about 8.8 Gy compared to 16.4 Gy for the B6CF1. The difference in LD50/6 between the parent strains or between BALB/c and the F1 hybrid could not be explained by any differences in crypt cell number, cell cycle time, or transit time. Likewise, the observed differences in the LD50/6 do not appear to result from marked differences in the radiosensitivity of marrow stem cells (CFU-S) since the D0's for the three genotypes of mice were similar. Also, there were no apparent differences in the red blood cell contents of several enzymes associated with antioxidant defenses. The microcolony assay was used to determine the D0 for the crypt clonogenic cells and the D0 values for 60Co gamma rays were about 0.8 Gy for BALB/c mice and 1.4 Gy for B6CF1 mice. However, the D0 values for JANUS fission neutrons were similar; 0.6 Gy for the BALB/c mice and 0.5 for the B6CF1 mice. A comparison of clonogenic cell kinetics, using prolonged colcemid block to distinguish between slowly and rapidly cycling cells suggest that, normally, the stem cells are slowly cycling in both the BALB/c and the B6CF1 hybrid. However, the stem cells of the B6CF1 appear to go into rapid cell cycle more rapidly than those of the BALB/c following irradiation or prolonged colcemid treatment. The more rapid recovery in intestinal epihelial cell production in the B6CF1 hybrid after irradiation may provide an increased mucosal barrier and may, in part, explain the difference in the response to radiation compared to that in the BALB/c. 相似文献
7.
Summary A new distinctive feature between the two Mediterranean species of Tethya, T. aurantium and T. citrina has been found in the body arrangement of different types of micrasters. Contrary to the previous assumptions, T. aurantium has two clearly distinct categories of micrasters: the chiaster-tylaster in the cortex and the larger, slender oxyaster in the choanosome. T. citrina has only slightly differentiated micraster sets in the cortex and choanosome; in the latter the shape of micrasters is close to that of oxyasters. SEM analysis shows that differences in micraster shape depend on the cylindrical or conical form of rays and on the distribution, density and strength of the microspines along their axis. The relationship between the degree of micraster differentiation and the development of the cortex in the two species is discussed. 相似文献
8.
Mauro Moresi Michele Patete Antonio Trunfio 《Applied microbiology and biotechnology》1989,31(5-6):495-501
Summary A whey fermentation by Kluyveromyces fragilis was scaled-up to a 1000-dm3 stirred fermentor, by varying the stirrer speed, the air-flow rate and the initial concentration of lactose. Its evolution was simulated by applying the same unstructured model (consisting of a microbial specific growth rate of pseudo-first order with respect to the COD concentration and constant biomass yield per unit COD removed) set up in previous experiments using 8- to 80-dm3 fermentors. Despite the great scale-up ratios, very different operating conditions, and geometric dissimilarity, a series of empirical regressions previously developed allowed approximate, but acceptable prediction of the stoichiometric and kinetic coefficients of the above mathematical model, thus confirming the capability of this model to provide a reliable basis for further scale-up of this fermentation process to a production scale. 相似文献
9.
Summary Binding of azide to a series of copper(II) complexes has been investigated by absorption, CD and EPR spectroscopy. Axial binding of azide to Cu(II) can be differentiated from equatorial binding through the lower intensity and lack of optical activity of the LMCT band. The affinity of azide for Cu(II) increases with the overall positive charge of the complex. The preliminary data on thiocyanate binding to Cu(II) seem to agree with the trends observed for the corresponding azide adducts. 相似文献
10.
Summary To extend the available information on the significance of the interactions between glycolytic enzymes and the actin component of the cellular ultrastructure, investigations into the compositional characteristics of the actin binding site on one of the major glycolytic enzymes, aldolase, have been undertaken. As the electrostatic nature of the association has been previously reported indicative of a cationic region on the enzyme involved in the binding, these studies have investigated the possibility of the involvement of histidine residues in this binding region. By the use of the histidine specific reagent, diethylpyrocarbonate, we have been able to establish a difference in nature of an actin binding domain and the active site domain which does contain an essential histidine. The results have been discussed in relation to the significance of this finding with respect to the binding of aldolase to subcellular structure. 相似文献