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SINCE the original observations by Wilson1 that dissociated sponge cells could reassociate in vitro, cell aggregation (or reaggregation) has been widely used as an operational criterion for the study of intercellular adhesion2. The introduction of rotation-mediated methods to promote cell aggregation3,4 led to the possibility of obtaining reproducible quantitative data. In these methods, suspensions of dissociated single cells are shaken under defined conditions of speed and temperature and cell aggregation is measured by either the size of aggregates or the number of single cells. The aggregation of dissociated cells from sponges5, chick and mouse embryos4 and tissue culture cells6 has been investigated with this method. Cells maintained in vitro seemed particularly suitable for studying mechanisms of cell aggregation as they represent a histotypically homogeneous population. 相似文献
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Giant muscle fibers of the barnacle give graded, relativelyslow contractions, A plateau level, termed the unit response,occurs with stimuli of 3 msec, but pulses longer than 1015msec give much greater tension or shortening. Repetitive stimulationwith pulses of 3 msec leads to a tetanus. The magnitude of activestate was determined, and found to be also graded in natureand slow to develop, though early in onset. The full developmentof active state requires 80120 msec. A high level ofeffective series-elasticity was associated with the sarcomeresthemselves. 相似文献
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CLAIRE DETRAIN FRANÇOIS J. VERHEGGEN LISE DIEZ BERNARD WATHELET ERIC HAUBRUGE 《Physiological Entomology》2010,35(2):168-174
Honeydew is the keystone on which ant–aphid mutualism is built. The present study investigates how each sugar identified in Aphis fabae Scopoli honeydew acts upon the feeding and the laying of a recruitment trail by scouts of the aphid‐tending ant Lasius niger Linnaeus, and thus may enhance collective exploitation by the ant mutualists. The feeding preferences shown by L. niger for honeydew sugars are: melezitose = sucrose = raffinose > glucose = fructose > maltose = trehalose = melibiose = xylose. Although feeding is a prerequisite to the launching of trail recruitment, the reverse is not necessarily true: not all ingested sugar solutions elicit a trail‐laying behaviour among fed scouts. Trail mark laying is only triggered by raffinose, sucrose or melezitose, with the latter sugar being specific to honeydew. By comparing gustatory and recruitment responses of ant foragers to sugar food sources, the present study clarifies the role of honeydew composition both as a source of energy and as a mediator in ant–aphid interactions. Lasius niger feeding preferences can be related to the physiological suitability of each sugar (i.e. their detection by gustatory receptors as well as their ability to be digested and converted into energy). Regarding recruitment, the aphid‐synthesized oligosaccharide (melezitose) could be used by ant scouts as a cue indicative of a long‐lasting productive resource that is worthy of collective exploitation and defence against competitors or aphid predators. 相似文献
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