ISSN:0886-1544    

DOI:10.1002/cm.970060302

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe membrane potential ofParameciumcontrols the frequency and direction of the ciliary beat, thus determining the cell's swimming behavior. Stimuli that hyperpolarize the membrane potential increase the ciliary beat frequency and therefore increase forward swimming speed. We have observed that (1) drugs that elevate intracellular cyclic AMP increased swimming speed 2–3‐fold, (2) hyperpolarizing the membrane potential by manipulation of extracellular cations (e.g., K+) induced both a transient increase in, and a higher sustained level of cyclic AMP compared to the control, and (3) the swimming speed of detergent‐permeabilized cells in MgATP was stimulated 2‐fold by the addition of cyclic AMP. Our results suggest that the membrane potential can regulate intracellular cAMP inParameciumand that control of swimming speed by membrane potential may in part be mediated

ISSN:0886-1544    

DOI:10.1002/cm.970060303

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

年代:1986

数据来源: WILEY

摘要:

AbstractDue to the recent observation that heparin binds to several growth factors and cell adhesion molecules, the effect of heparin on biological processes governed by growth factors and cell adhesion molecules was investigated. Pharmacological doses of heparin were found to alter cell growth rate, cellular morphology, and cell motility.Concentrations (μg/ml) of heparin or dextran sulfate decreased cell growth rate, but not the final cell density attained in plateau phase. The effect of heparin on cell growth rate was most pronounced when cells were cultured in low concentrations of serum. A heparin‐induced decrease in cell growth rate could be reversed by addition of platelet‐derived growth factor (PDGF), a heparin‐binding growth factor.Heparin altered the morphology of all cell lines studied to various degrees. The effect of heparin on cell morphology was quantitated by measuring the heparin‐induced change in cell surface area. HT‐1080 and HeLa cells nearly doubled in surface area upon exposure to 10μg/ml heparin. Since several heparin‐binding cell adhesion proteins mediate both cell spreading and cell migration, the influence of heparin on cell migration was investigated with an improved version of the phagokinetic track technique. Low concentrations of heparin and dextran sulfate were found to increase the rate of cell migration in a dose‐dependent fashion.Since the quantitative effect of heparin on cell growth rate, morphology, and migration depends on the cell line studied, it is suggested that three separate phenomena may be involved. The results presented indicate a central role for sulfated glycosaminoglycans in the control of both cell growth and cell‐

ISSN:0886-1544    

DOI:10.1002/cm.970060304

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

年代:1986

数据来源: WILEY

摘要:

AbstractWe have analyzed the effect of colchicine and tubulin dimer‐colchicine complex (T‐C) on microtubule assembly in mitotic spindles. Cold‐ and calcium‐labile mitotic spindles were isolated from embryos of the sea urchinLytechinus variegatusemploying EGTA/glycerol stabilization buffers. Polarization microscopy and measurements of spindle birefringent retardation (BR) were used to record the kinetics of microtubule assembly‐disassembly in single spindles. When isolated spindles were perfused out of glycerol stabilizing buffer into a standard in vitro microtubule reassembly buffer (0.1 M Pipes, pH 6.8, 1 mM EGTA, 0.5 mM MgCl2, and 0.5 mM GTP) lacking glycerol, spindle BR decreased with a halftime of 120 s. Colchicine at 1 mM in this buffer had no effect on the rate of spindle microtubule disassembly. Inclusion of 20 μM tubulin or microtubule protein, purified from porcine brain, in this buffer resulted in an augmentation of spindle BR. Interestingly, in the presence of 20 μM T‐C, spindle BR did not increase, but was reversibly stabilized; subsequent perfusion with reassembly buffer without T‐C resulted in depolymerization. This behavior is striking in contrast to the rapid depolymerization of spindle microtubules induced by colchicine and T‐C in vivo. These results support the current view that colchicine does not directly promote microlubule depolymerization. Rather, it is T‐C complex that alters microtubule assembly, by reversibly binding to microtubules and inhibiting elongation.In vivo, colchicine can induce depolymerization of nonkinetochore spindle microtubules within 20 s. In vitro, colchicine blocks further microtubule assembly, but does not induce rapid disassembly. The rate of tubulin dissociation from spindle microtubules in vitro in reassembly buffer without soluble tubulin is about 20 times slower than the rate of dissociation in vivo when assembly is blocked abruptly by T‐C. The rate of tubulin dissociation from the spindle microtubules may determine their response to T‐C, since the tubulin dissociation rate in vivo is about 12 times faster than the rate measured here for spindle microtubules in standard microtubule reassembly buffer at ph

ISSN:0886-1544    

DOI:10.1002/cm.970060305

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

年代:1986

数据来源: WILEY

摘要:

AbstractAntitubulin, phalloidin. and antimyosin were used to study the distribution of microtubules, microfilaments, and myofibrils in cultured adult cardiomyocytes. These cells undergo a stereotypic sequence of morphological change in which myotypic features are lost and then reconstructed during a period of polymorphic growth. Microtubules, though rearranged during these events in culture, are always present in an organized network. Myosin and actin structures, on the other hand, initially degenerate. This initial degeneration is reversed when a cell attaches to the culture substratum. Upon attachment, new microtubules are laid down as a cortical network adjacent to the sarcolemma and, subsequently, as a network in the basal part of the cell. Actin and then myosin filament bundles appear next, in a pattern corresponding to the pattern of the microtubules. Finally, striated myofibrils are formed, first in the central part of the cell, and subsequently in the outgrowing processes of the cell, A mechanism is suggested by which the eventual polymorphic shape of a cell is related to the shape of its initial area of contact with the culture substratum. Finally, a model of myofibrillogenesis is proposed in which microtubules participate in the insertion of myosin among previously formed actin filament bundles to produce myofibrils.

ISSN:0886-1544    

DOI:10.1002/cm.970060306

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

年代:1986

数据来源: WILEY

摘要:

AbstractCytoplasmic streaming and its response to azide and low temperature were examined by using high‐resolution video‐enhanced light microscopy inSetcreasea purpureastaminal hair cells of immature flowers. Particles and organelles examined moved along well‐defined pathways, in repeated and unequal saltatory steps, at different rates and sometimes against the main direction of flow (bidirectionally) in both transvacuolar strand and peripheral cytoplasm. Particle movements were reversibly inhibited with azide. Low temperatures caused transvacuolar strands to shift or break. This cytoplasm accumulated in areas outside of the vacuole where spherosomes continued to saltate, but not along well‐defined pathways. In the peripheral cytoplasm, however, the spherosomes continued to move normally, amyloplasts became swollen, and they plus the other organelles (except spherosomes) were stationary. Normal particle movements were obtained when chilled cells were rewarmed to 27°C for c

ISSN:0886-1544    

DOI:10.1002/cm.970060307

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

年代:1986

数据来源: WILEY

摘要:

AbstractSodium‐orthovanadate (100–700 μM) added to purified pig brain microtubule protein (molar ratios 13–90 moles vanadate/mole tubulin) inhibits to a considerable extent the assembly (up to 65%) and the disassembly rates (up to 60%) of microtubules, as determined by turbidimetry. Vanadate added to preformed microtubules did not appreciably alter the turbidity level of the samples, however, the disassembly rates were decreased in the same manner as when vanadate was added prior to polymerization. Microtubule protein kept on ice for 3–6 hours became more susceptible to vanadate than freshly prepared protein. The effect of vanadate was independent of the GTP concentration at which the polymerization assays were performed (0.025 to 1 mM GTP). In the presence of taxol, which increases the rate and extent of microtubule formation, vanadate had no effect on assembly rates. Disassembly was inhibited, however, much less than in the presence of vanadate alone. Electron microscopy and polyacrylamide gel electrophoresis did not reveal differences between microtubules prepared in the presence or in the absence of vanadate. This is consistent with the notion that vanadate does not interfere with the interaction between tubulin and the high‐molecular weight microtubule‐associated proteins. Apparently vanadate brings about an allosteric change of the microtubule protein(s) resulting in the abnormal polymerization kinetics of tubulin found in our study. The above results may be relevant for studies where the effects of vanadate on intracellular motility are interpreted as being solely due to a specific inhibitio

ISSN:0886-1544    

DOI:10.1002/cm.970060308

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

年代:1986

数据来源: WILEY

摘要:

AbstractReports on how changes in microtubule (MT) distribution or polymerization affect the distribution of intermediate filaments (IFs) differ. Therefore, we have used cytoimmunofluorescence techniques and electron microscopy to systematically examine and compare the arrangements of MTs and IFs in cultures of chick embryo fibroblasts under the following conditions: at different times during the cell cycle, in the presence of Colcemid or of taxol, in the presence of both drugs in succession or simultaneously in varying ratios, and during recovery from treatment with Colcemid or taxol.We have found that depolymerization of MTs by 1 μM Colcemid resulted in the rapid formation of massive IF‐cables, structures distinct from “collapsed IFs” or “juxtanuclear coils.” Neither the rapid formation of IF‐cables nor their dispersion during recovery required protein synthesis. Cells treated with 10 μM taxol rapidly formed MT‐bundles, as well as aggregates of intertwining IFs, termed “IF‐skeins.” MT‐bundles and IF‐skeins displayed strikingly complementary distributions. This reciprocal distribution of packed MTs and IFs was also obvious in untreated anaphase and telophase cells. When 10 μM taxol and 1 μM Colcemid were applied simultaneously, the complementary distributions of MT‐bundles and IF‐skeins mimicked those in taxol alone. This ability of taxol to block Colcemid's effects was concentration dependent Decreasing the taxol:Colcemid ratio allowed the depolymerization of MTs, which correlated

ISSN:0886-1544    

DOI:10.1002/cm.970060309

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe mechanism by which organelles are transported bidirectionally in axoplasm is still unknown; however, evidence of a key role for microtubules in many nonmammalian models has been established. We have observed common or shared tracks within the axoplasm of human nerves along which multiple organelles of varying size and shape are bidirectionally transported. Organelles traveling anterogradely and retrogradely were visualized by video‐enhanced differential interference contrast optics and analyzed with the aid of computer‐image‐processing techniques.Speeds of translocating organelles were determined at eight to 16 translocation points along a path or “track.” Each translocation speed was plotted against its corresponding position on the track to develop a “speed/position diagram.” Regardless of mean organelle speed or direction of motion, organelles sharing a common track exhibited similar patterns of “speeding up” and “slowing down” relative to position along the track. Speed position data for organelles translocating the local axonal region of a common track showed no unique patterns (not different from a uniform distribution, p<0.05). The unique speed/position patterns exhibited by common tracks were not necessarily related to the patterns of other tracks in the immediate vicinity (distance between tracks of<0.50 μm). These findings suggest that (1) there are “common tracks” shared by organelles moving retrogradely and anterogradely; (2) both the organelles and the “track” associated with its translocation play a role in the resultant motion of that organelle; (3) the influence exerted by a common track on the motion of an organelle results in a pattern of speed changes relat

ISSN:0886-1544    

DOI:10.1002/cm.970060310

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe generation of bending waves by microtubules in squid nerve axoplasm has been modelled using appropriately modified versions of computer programs developed previously for simulation of flagellar bending waves. The results confirm that a constant longitudinal force directed along the axis of the microtubule is sufficient to cause the generation of regular oscillations and propagated bending waves when the forward gliding movement of the microtubule is obstructed. No control mechanism is required to modulate the active force‐generating system. In order to obtain bending waves similar to those observed experimentally, it was necessary to use a model for the force‐generating system in which the active force decreases with increasing sliding velocity. If the elastic bending resistance of axoplasmic microtubules is similar to that of microtubules in sperm terminal filaments, the longitudinal force per unit length generated by the axoplasmic microtubules must be of the same order of magnitude as the force generated by dynein arms along the doublet microtubules of eukaryotic flage

ISSN:0886-1544    

DOI:10.1002/cm.970060311

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

年代:1986

数据来源: WILEY