摘要:

AbstractBrain or muscle F‐actin is rapidly depolymerized to monomeric actin in vitro by actin‐depolymerizing factor, a protein isolated from chick embryo brain. Binding of muscle tropomyosin to muscle F‐actin protects the F‐actin from depolymerization by this factor. A 8.4/1.0 molar ratio of actin subunits to tropomyosin, achieved by incubation of the F‐actin with excess tropomyosin, protects 58% of the F‐actin from depolymerization by excess actin‐depolymerizing factor for at least 3 hr at 25°C. Thus, actin‐depolymerizing factor seems to be specifically directed toward actin filaments lac

ISSN:0271-6585    

DOI:10.1002/cm.970020102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractTwo phases of prey capture by the heliozoon Actinophrys sol are documented by electron microscopy. The phases are those of prey adhesion to the predator and enclosure of the prey by the predator. Adherence is brought about by numerous small pieces of adhesive membrane produced by the predator at the site of prey contact. Some of the heliozoan extrusomes expel their contents at this time, but the significance of this event is unclear. Enclosure of the prey is effected by a funnelshaped pseudopodium. This is drawn over the prey by the action of the leading margin. The ultrastructural appearance of the cytoplasm of the leading margin differs from the rest of the cell, being homogeneous and finely filamentous. Both force and traction for the progression of the pseudopod are generated primarily at the tip. During the development of the funnel‐pseudopod, extrusomes expand and fuse with each other and with the plasma membrane. Their investing membrane is thereby made available as food vacuole membran

ISSN:0271-6585    

DOI:10.1002/cm.970020103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractUsing a line of epithelial cells (SCCA5) derived from a spontaneous rat carcinoma, the glucose analogue 2‐deoxyglucose (2DG) has been shown by time‐lapse cinemicrography to produce a cessation of motility by 1 hour that can be reversed by replacement of the 2DG, and does not occur in equivalent media with or without glucose or in 2DG‐containing media with added pyruvate and citrate. The effect on the cells at the edge of an epithelial island is to prevent the formation of new lamellipodia and produce a progressive retraction and condensation of lamellipodia already present. This effect of 2DG on motility corresponds with a significant reduction in the level of ATP that is partially restored after 30 minutes in the recovery incubation. Only a slight reduction in protein synthesis occurs in the presence of 2DG. The external morphology and the cytoplasmic ground substance of the cells were studied by scanning electron microscopy and high voltage electron microscopy respectively. It was found that after incubation in 2DG for 1 hour the outline of the free edges of the cells was distorted resulting in redistribution of microvilli, condensation of cytoplasm into strands, and irregular projections from the edges of residual lamellipodia. The structure of the cytoplasmic ground substance in lamellipodia from cells incubated in 2DG for 3 hours was distinctly different from that in cells incubated for 3 hours in 2DG then recovered for 25 minutes, or in cells incubated in glucose‐containing medium for 3 hours. In the 2DG‐treated cells the lattice‐like structure evident in critical‐point‐dried cells was condensed into short thick strands that terminated in bulbous ends, whereas in cells recovered for 25 minutes the lattice material was elongated and tapering and the interlattice space relatively expanded. The results obtained support the concept of modulation occuring in the structure of the microtrabecular lattice component of the cytoplasmic ground substance coincident with alterations in cell function and

ISSN:0271-6585    

DOI:10.1002/cm.970020104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe role of microtubules in secretory granule translocation was studied during stalk secretion in the peritrich ciliate, Zoothamnium arbuscula. In each cell, the release of stalk‐forming secretory materials is restricted to a specialized region of the cytoplasm, the scopula. Many of the membrane‐bound secretory granules that dominate the scopular cytoplasm appear to be aligned along cortical microtubules that converge on the scopular surface. This arrangement is consistent with the hypothesis that microtubules transport granules relative to the sites of exocytosis. To establish the role of microtubules in stalk secretion, telotrochs were exposed to agents with different disruptive effects on microtubule function. Exocytosis itself is not prevented by these drugs, and granules positioned for secretion prior to treatment are released. Maytansine and isopropyl‐n‐phenyl carbamate (IPC) completely inhibit stalk elongation. In maytansine‐treated cells, microtubules are absent from the scopular cytoplasm, and granules are absent from the scopular surface. Microtubules are present in IPC‐treated cells, but the granules are misdirected to the cytoplasm lateral to the scopula where no secretory sites exist. Even though the rate of stalk secretion is decreased by deuterium oxide (D2O), a control length stalk is eventually produced. In D2O‐treated cells microtubules are present and in their normal orientation. The inhibition of secretion when microtubules are absent (maytansine) or misdirected (IPC) and the retardation of secretion when microtubule turnover is reduced (D2O) supports a mechanism of granule transport based on the directional turnover of microtu

ISSN:0271-6585    

DOI:10.1002/cm.970020105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe effects of the uncouplers CCCP and DNP on photokinesis, phototaxis, and the photophobic response in the desmid Cosmarium have been studied both in population systems and by videomicrographic, single‐cell analysis. Light‐dependent motility is specifically inhibited by both uncouplers, indicating that photokinesis is driven by photophosphorylation. In population experiments, phototaxis and accumulations in light traps due to photophobic responses are inhibited by drug concentrations comparable to those that inhibit photokinesis. Analysis of single‐cell behavior demonstrated, however, that neither photophobic responses elicited by an increase in light intensity (step‐up response) nor by a decrease (stepdown response) are inhibited, as long as the reduced motility allows the organisms to cross a light‐‐dark border. Phototactic orientation is not impaired by DNP in the single cell analysis, but CCCP significantly reduced the degree of orientation. The results indicate that, although chlorophyll is the photoreceptor for all three photoresponses, at least the photophobic response is independent of both the photosynthetic electron transport chain and photophos

ISSN:0271-6585    

DOI:10.1002/cm.970020106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

ISSN:0271-6585    

DOI:10.1002/cm.970020107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

ISSN:0271-6585    

DOI:10.1002/cm.970020108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

ISSN:0271-6585    

DOI:10.1002/cm.970020101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY