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PubMed2003

The amount of sleep obtained by locomotive engineers: effects of break duration and time of break onset.

AIMS: To determine the effects of break duration and time of break onset on the amount of sleep that locomotive engineers obtain between consecutive work periods. METHODS: A total of 253 locomotive engineers (249 male, 4 female, mean age 39.7 years) participated. Data were collected at 14 rail depots, where participants drove electric or diesel locomotives; worked with another engineer or drove alone; carried passengers, freight, or coal; and operated in rural or urban areas. Participants completed sleep diaries and work diaries for a two week period while working their normal roster patterns. RESULTS: For breaks that began at similar times of day, total sleep time (TST) increased with break duration. For breaks of similar duration, TST was greater for those that occurred during the night-time than for those that occurred during the daytime. An average of 3.1-7.9 hours sleep was obtained in 12 hour breaks (minimum break requirement in the Australian rail industry), depending on when the break began. CONCLUSIONS: The duration and timing of breaks are both important factors in determining the amount of sleep that locomotive engineers obtain between consecutive work periods. Consequently, minimum length break requirements that do not include a time of day component may not provide locomotive engineers with the opportunity to obtain a sufficient amount of sleep prior to resuming work.

Adult↗
PubMed1991

An intracellular study of muscle primary afferents during fictive locomotion in the cat.

1. Presynaptic activity of identified primary afferents from flexor, extensor, and bifunctional hindlimb muscles was studied with intra-axonal recordings during fictive locomotion. Fictive locomotion appeared spontaneously in decorticate cats (n = 9), with stimulation of the mesencephalic locomotor region (n = 4), and in spinal cats injected with clonidine or nialamide and L-DOPA (n = 4). Representative flexor and extensor muscle nerves, recorded to monitor the locomotor pattern and dorsal rootlets of the sixth and seventh lumbar segments, were recorded simultaneously to monitor dorsal root potentials (DRPs). 2. From responses to muscle stretches and, in some instances, twitch contractions of the parent muscle, 75% of the single units examined were putatively identified as spindle afferents (40/53). On the basis of conduction velocity and stimulation threshold, 73% of these were further classified as group I fibers (29/40), the rest as group II fibers. 3. All units (n = 53 with resting potential more negative than -45 mV) showed fluctuations of their membrane potential (up to 1.5 mV) at the rhythm of the fictive locomotion. Subsequent averaging of these fluctuations over several cycles revealed that 89% of all units displayed a predominant wave of depolarization during the flexor phase, followed by a trough of repolarization. In 79% of the units, there was also a second, usually smaller, depolarization during the extensor phase. The relative size of each wave of depolarization could vary with different episodes of fictive locomotion in the same unit and among various afferents from the same muscle in the same experiment. 4. The firing frequency of some afferents from the ankle flexor tibialis anterior (5/16) and the bifunctional muscle posterior biceps-semitendinosus (4/15) was phasically modulated along the fictive step cycle. The maximum frequency always occurred during the flexor phase, i.e., during the largest depolarization of the unit. Because of the absence of phasic sensory input in the curarized animal, we assume that the phasic discharges were generated within the spinal cord and antidromically propagated. Phasic firing was never encountered in afferents from extensor muscles such as triceps surae (0/15) and vastus lateralis (0/4). 5. The results demonstrate that the pattern of rhythmic depolarization accompanying fictive locomotion is similar for the majority of flexor, extensor, and bifunctional group I (and possibly group II) muscle spindle primary afferents. They further indicate that there is a specific phasic modulation of antidromic firing for some flexor and bifunctional muscle spindle afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

Impaired neutrophil locomotion during acute bacterial infections.

Neutrophils from patients with acute bacterial infections show a marked decrease in random as well as directional locomotion in vitro. The further analysis of the data suggests that defective directional locomotion is due to impaired locomotion and not to impaired chemotaxis. The defect disappeared almost completely with clinical recovery. There was no direct correlation between impaired directional neutrophil locomotion and the proportion of band forms in the neutrophil population. Plasma obtained from patients with acute bacterial infections showed no 'spontaneous' chemotactic activity and immune complex-induced cytotaxin formation was normal in vitro. Neutrophils from 2 patients with viral pneumonia showed normal locomotion.

Acute Disease↗
PubMed1993

Effects of extracellular matrix components on cell locomotion.

The extracellular matrix (ecm), which is composed of collagens, glycoproteins, and proteoglycans, has emerged as an important regulator of cell locomotion. This review describes some of the mechanisms by which the ecm may regulate locomotion, focusing primarily on cell extension and lamellae formation. Ecm-receptor interactions form an important part of cell recognition of ecm. Such interactions can result in altered cell adhesion, signal transduction, and cytoskeletal organization, all of which impact on cell locomotion. It is important to note that although the effects of single ecm components have been studied, generally, the cell is likely to perceive ecm in vivo as a macromolecular complex. It will fall to future work to define how complexes of ecm regulate cell behavior. Because of our own particular research bias, we focus on reviewing the role of fibronectin, integrins, chondroitin sulfate, hyaluronan, and hyaluronan receptors in the regulation of cell locomotion and examine their effect on adhesion, signal transduction, and cytoskeletal integrity. Cytoskeleton assembly mechanisms, particularly those that might be regulated by the ecm, are also described. These events are summarized in a working model of ecm-promoted locomotion.

Animals↗
PubMed1994

Dispersive locomotion of human neutrophils in response to a steroid-induced factor from monocytes.

A monocyte-derived factor that stimulates the locomotion of human neutrophils on an albumin-coated glass surface has been prepared from the culture supernatant of dexamethasone-treated human monocytes and called STMS (steroid-treated monocyte supernatant). A modified cell tracking program has been developed and the parameters of locomotion determined by the analysis of Gail and Boone for cells moving in a persistent random walk. Cells moving in uniform concentrations of STMS, interleukin-8 (IL-8) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) chosen to give a sub-maximal speed of locomotion show persistent, random and constrained random diffusion, respectively, with augmented diffusion coefficients of 0.8 +/- 0.1, 0.14 +/- 0.02 and 0.12 +/- 0.03 microns 2 per second for STMS, IL-8 and fMLP, respectively. The augmented diffusion coefficient and the underlying persistence are therefore sensitive quantitative assay parameters for STMS activity and the qualitative characteristics of locomotion allow STMS activity to be distinguished from that of all other factors tested. The contribution of lowered adhesion to locomotion was examined in a novel tilt-assay, which demonstrated that cells in the presence of STMS, but not other factors, moved down slope with significantly increased speed while maintaining contact with the substratum. The results were interpreted in terms of the bipolar form of STMS-treated cells, contrasting with multipolar forms in response to other agents. This together with low adhesiveness plus an inherent tendency of a single locomotor focus to continue motion in its original direction has been used to explain the difference between response to STMS and other factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Adhesion↗
PubMed1978

Non-reciprocal contact inhibition of locomotion of chick embryonic choroid fibroblasts by pigmented retina epithelial cells.

Using light and electron microscopy, we have confirmed an earlier observation that chick embryonic pigmented retina epithelial cells (PRE cells) seeded in vitro on cultured sheets of choroid fibroblasts, are able to spread. Spreading is as rapid (and shows the same dependence on lateral contact between PRE cells) as on a serum-coated culture substrate. After 1 h most cells are spreading on the upper surface of the choroid sheet, but after 4 h, some PRE cells can be found sandwiched between overlapping choroid cells, and thus have invaded the sheet. Choroid fibroblasts underlie PRE in vivo, but the ability of PRE cells to spread on cultured fibroblasts is not specific for choroid, since PRE cells spread also on BKH21 hamster kidney fibroblasts, and on fibroblasts from chick embryonic heart. As reported by others for various fibroblastic cells, choroid cells seeded on to choroid sheets or on to cultured PRE are unable to spread. A possible explanation is that spreading of adherent cells is contact-inhibited by the cells in the sheet, just as their leading edges are paralysed on contact, and thus locomotion is inhibited, when fibroblasts collide on a plane substratum. If spreading of seeded cells and cell locomotion are inhibited by the same mechanism, PRE cells should contact-inhibit choroid fibroblasts with which they collide, but not themselves be so inhibited. Using time-lapse cinemicrography, we have found this to be the case. We first established that in homotypic collisions, choroid fibroblasts do show contact inhibition of locomotion, despite the criss-cross (not well monolayered) appearance of confluent cultures. In heterotypic collisions between choroid and PRE we found the predicted nonreciprocal behaviour: the choroid leading edge is paralysed on collision, and the cell subsequently retracts, whereas the active PRE margin appears to be completely unaffected. Speed measurements from a series of such collisions show that the speed of choroid cells is markedly reduced on collision with PRE, whereas the slight slowing of PRE is not statistically significant. We have observed similar behaviour in heterotypic collisions between various epithelial and fibroblastic cells, and so it seems possible that non-reciprocity may prove general for this interaction. If so, it has important implications for the role of contact inhibition of locomotion in phenomena such as morphogenesis, wound healing and the invasiveness of carcinoma cells. On the one hand, non-reciprocal contact-inhibition of locomotion may permit the spreading of epithelia over mesenchymal cells, thus generating or restoring an epithelial bounding membrane. On the other hand, in the absence of other interactions, it would fail to inhibit the invasion of mesenchymal territory by aberrant epithelial cells, or presumably by epithelial free edges.

Animals↗
PubMed1995

Initiation of locomotion by lateral line photoreceptors in lamprey: behavioural and neurophysiological studies

The lateral line system of lampreys includes photoreceptors distributed in the skin of the tail region. These are innervated by the trunk lateral line nerves, and the afferents terminate bilaterally in the medial octavolateral nucleus, crossing the midline through the cerebellar commissure. Stimulation of the dermal photoreceptors by tail illumination initiates locomotion. The present study was performed to characterize the response to illumination in larval and adult lampreys in detail and to elucidate the neuronal pathways responsible for the activation of locomotion. In both larval and adult quiescent lampreys, the response to unilateral illumination of the tail was found to consist of an initial turn followed by rectilinear swimming. The sign and magnitude of the turning angle were not correlated with the laterality of the optic stimulus. In mechanically restrained lampreys, spinalized at the level of segments 15&shy;20, tail illumination evoked a complex motor response in the rostral part of the body, with switches between different patterns of coordination (turns in different directions, locomotion, and turns combined with locomotion). Thus, the response to tail illumination is not a simple reflex, but includes a behavioural choice. Reticulospinal neurones play a crucial role in the initiation of locomotion in lampreys. The response to unilateral tail illumination in rhombencephalic reticular cells was studied with extracellular single-unit recordings. It was found that neurones in the middle and posterior rhombencephalic reticular nuclei were activated bilaterally. Tonic activity or slow bursts (<0.5 Hz) were evoked, in some cases lasting up to 60 s after the stimulation. The response remained bilateral after transection of one lateral line nerve and the cerebellar commissure. Afferents from one side can thus activate reticulospinal cells on both sides through a pathway outside the cerebellar commissure. This bilateral activation of reticulospinal neurones is presumably responsible for the activation of spinal locomotor networks, without any directional bias to the left or the right side, and for the rectilinear swimming observed in behavioural experiments. In the caudal part of the termination area of the lateral line nerve afferents, neurones with contralateral projections were retrogradely stained with horseradish peroxidase. These neurones appear to be likely candidates for mediating the contralateral effects of the lateral line fibres.

Journal Article↗
PubMed2000

Three-dimensional kinematics and wake structure of the pectoral fins during locomotion in leopard sharks Triakis semifasciata.

The classical theory of locomotion in sharks proposes that shark pectoral fins are oriented to generate lift forces that balance the moment produced by the oscillating heterocercal tail. Accordingly, previous studies of shark locomotion have used fixed-wing aircraft as a model assuming that sharks have similar stability and control mechanisms. However, unlike airplanes, sharks are propelled by undulations of the body and tail and have considerable control of pectoral fin motion. In this paper, we use a new approach to examine the function of the pectoral fins of leopard sharks, Triakis semifasciata, during steady horizontal swimming at speeds of 0.5-2.0ls(-1), where l is total body length, and during vertical maneuvering (rising and sinking) in the water column. The planar orientation of the pectoral fin was measured using three-dimensional kinematics, while fluid flow in the wake of the pectoral fin and forces exerted on the water by the fin were quantified using digital particle image velocimetry (DPIV). Steady horizontal swimming in leopard sharks is characterized by continuous undulations of the body with a positive body tilt to the flow that decreases from a mean of 11 degrees to 0.6 degrees with increasing flow speeds from 0. 5 to 2.0ls(-1). Three-dimensional analysis showed that, during steady horizontal locomotion, the pectoral fins are cambered, concave downwards, at a negative angle of attack that we predict to generate no significant lift. Leopard shark pectoral fins are also oriented at a substantial negative dihedral angle that amplifies roll moments and hence promotes rapid changes in body position. Vortices shed from the trailing edge of the pectoral fin were detected only during vertical maneuvering. Starting vortices are produced when the posterior plane of the pectoral fin is actively flipped upwards or downwards to initiate rising or sinking, respectively, in the water column. The starting vortex produced by the pectoral fin induces a pitching moment that reorients the body relative to the flow. Body and pectoral fin surface angle are altered significantly when leopard sharks change vertical position in the water column. Thus, locomotion in leopard sharks is not analogous to flight in fixed-wing aircraft. Instead, a new force balance for swimming leopard sharks is proposed for steady swimming and maneuvering. Total force balance on the body is adjusted by altering the body angle during steady swimming as well as during vertical maneuvering, while the pectoral fins appear to be critical for initiating maneuvering behaviors, but not for lift production during steady horizontal locomotion.

Animals↗
PubMed2001

Locomotion of lymphocytes towards melanoma cells treated with tumor necrosis factor in a syngeneic in vitro model.

Tumor necrosis factor (TNF) causes cell necrosis in vivo by damaging the endothelium of the neovasculature. However, its mechanism of action is not well understood. We hypothesized that TNF affects the tumor microenvironment even before neovascularization occurs, thereby increasing lymphocyte locomotion through the peritumoral matrix, a crucial step in tumor cell killing. The effect of TNF on lymphocytes was tested with the type I rat-tail collagen mini-assay in peripheral blood lymphocytes (PBL) from normal donors, a non-migratory PBL cell line (HPB), and a C3H mice splenic lymphocytes. Melanoma cell line (k1735p) was treated with TNFalpha/TNFbeta 10 or 20 pg/microl. The syngeneic splenic lymphocytes were layered on top of the collagen, and their migration into the collagen towards the tumor cells was assessed. Tumor cell viability was evaluated before and after TNF treatment. Paired two-tailed Student's t-test was used for statistical analysis. TNFalpha and TNFbeta had no significant direct effect on locomotion of PBL or HPB. Lymphocyte locomotion was inhibited in the presence of untreated melanoma cells in 7 of 9 assays (statistically significant in four), and it was significantly increased towards TNFalpha- or beta-treated melanoma cells, compared to untreated condition, in 7 of 9 assays (p=0.05 to p=0.0001). The number of viable tumor cells was not significantly different before and after treatment. In conclusion, treatment of tumor cells with TNFalpha or TNFbeta significantly enhances lymphocyte locomotion through the matrix. The effect of TNF is not the result of a direct influence on the lymphocytes, and is not associated with a decrease in the number of viable tumor cells. These findings suggest that TNF interaction with the cell microenvironment induces a change in lymphocyte locomotion.

Animals↗
PubMed2000

Neutrophil polarity and locomotion are associated with surface redistribution of leukosialin (CD43), an antiadhesive membrane molecule.

This study analyzed the behavior of an antiadhesive membrane molecule, CD43, in neutrophil polarization and locomotion. CD43 cross-linking by antibodies induced neutrophil locomotion, with CD43 molecules clustered at the uropod of polarized neutrophils. In contrast, CD11b/CD18 cross-linking by antibodies did not affect either cell polarization or locomotion. Stimulation of suspended or adherent neutrophils with chemotactic peptide results in cell polarization and locomotion and a concomitant redistribution of CD43 to the uropod. This process is entirely reversible. The study also investigated which actin-binding protein could be involved in CD43 lateral redistribution. alpha-Actinin and moesin are preferentially adsorbed on Sepharose beads bearing a recombinant CD43 intracellular domain. Analysis by immunofluorescence confocal microscopy shows a codistribution of moesin during CD43 lateral redistribution. By contrast, alpha-actinin is located at the leading edge, an area devoid of CD43. These results shed new light on the role of CD43 membrane redistribution, which appears to be directly related to neutrophil polarity and locomotion. (Blood. 2000;95:2462-2470)

Adult↗
PubMed2004

Locomotion in simulated zero gravity: ground reaction forces.

BACKGROUND: Exercise is likely to be an important countermeasure to bone demineralization, which remains a concern for astronauts during long-duration spaceflight. However, loads on the feet during exercise with 1 G equivalent gravity replacement are not known. The purpose of this study was to compare ground reaction forces (GRFs) during over-ground and simulated zero gravity (0 G) locomotion. HYPOTHESIS: It was hypothesized that sufficient gravity replacement loading could be applied to the subjects such that GRF profiles similar to those seen in 1 G would occur during locomotion in a zero-gravity locomotion simulator (ZLS). METHODS: GRFs were measured during overground walking and running, and during locomotion in two restraint harness designs in the ZLS with an initial loading of 1 body weight. Load cells measured the gravity replacement load (GRL) in the ZLS. Joint angles at the hip and knee were also measured by goniometers. RESULTS: Peak forces were greater in overground locomotion than in the ZLS; however, loading rates were greater in the ZLS running conditions than in overground running. The knee joint was more flexed at key times in the support phase during running in the ZLS compared with overground. CONCLUSIONS: Large loads and loading rates can be generated at the feet during simulated 0 G exercise although peak forces during running in the ZLS are less than overground running at the same speed. The refinement of the gravity replacement system to provide a constant 1 G load should be considered.

Adult↗
PubMed1990

[Monocyte locomotion inhibiting factor (MLIF) produced by E. histolytica induces an increase of cAMP in human monocytes].

The supernatant fluid of axenically grown E. histolytica contains a factor (MLIF) which inhibits the locomotion of human monocytes (including chemotaxis) without affecting that of human polymorphonuclear leucocytes. Locomotion, like other cellular functions, is modulated by changes in intracellular cAMP and cGMP. The consensus--with some exceptions--is that while rises in cGMP accompany locomotion, an increase in cAMP (without a concomitant fall in -cGMP) occurs with inhibition of cellular movement. We measured by radioimmunoassay the cAMP concentration of human monocytes exposed to inhibitory concentrations of MLIF. A significant (p less than 0.005) rise in monocyte cAMP was found, comparable to that observed with the use of forskolin, a well known cAMP stimulator. The control studies using plain axenic medium, not only failed to reveal any rise in cAMP but disclosed a small, yet not significant drop in intracellular cAMP. These results suggest that MLIF (like other locomotion inhibitors, i.e. prostaglandins E1, A1 and isoproterenol) produces a significant increase in intracellular monocyte cAMP. This modification in intracellular signals may contribute to the inhibition in monocyte locomotion, an event during which an increase in pericentriolar microtubules has also been observed.

Animals↗
PubMed1990

Chemoattractant stimulation of polymorphonuclear leucocyte locomotion.

Chemoattractants stimulate both cell locomotion and the orientation of this locomotion (chemotaxis) in polymorphonuclear leukocytes. Cell locomotion is a complex process which includes the coordinated protrusion of cell processes, formation of attachments to the substrate and contraction of the rear of the cell. To understand how chemoattractants regulate this process, it is helpful to dissect the process into components that can be examined separately. Comparison of these components in cells before and after stimulation with chemoattractant provides information about their regulation. In this review we focus on three components: how chemoattractants induce the development of cell polarity; how chemoattractants modulate cytoskeletal components (especially actin) to cause pseudopod protrusion; and how chemoattractant modulation of cell adhesions might contribute to cell locomotion. Spatial and temporal coordination of these and other components of locomotion result in efficient and directed cell movement. Our treatment of these questions is speculative and not comprehensive. We propose simple hypothetical models which can provide the reader with a conceptual framework that integrates the information available.

Actins↗
PubMed1990

In vitro migration of lymphocytes through collagen matrix: arrested locomotion in tumor-infiltrating lymphocytes.

Antitumor immunity requires (a) extravasation of lymphocytes from the blood stream to interstitium, (b) locomotion through extracellular matrix to the site of the tumor, (c) effector cell recognition of the tumor target with cell/cell contact and binding of adhesion receptors, (d) T-cell receptor binding to histocompatibility and tumor antigens, and (e) tumor cell lysis. We hypothesize that the tumor microenvironment inhibits lymphocyte locomotion through extracellular matrix as one mechanism by which tumors may avert host defense. Lymphocyte locomotion was investigated in vitro using a three-dimensional collagen gel model. Fresh tumor-infiltrating lymphocytes (TIL) were obtained by enzymatic digestion of melanomas and renal cell carcinoma, and mononuclear cells were isolated by discontinuous Ficoll-Hypaque gradient. The lymphocytes were analyzed for motility from a point of origin between basal and overlay layers of collagen gel. Results showed that TIL migration was almost completely inhibited, compared with migration of normal and cancer patient peripheral blood leukocytes and lymphocytes from lymph nodes. Short-term (24-h) exposure of lymphocytes to cytokines during the assay in the collagen gel matrix had no effect on locomotor ability. Long-term (19, 30, or 35 days) culture of TIL in 200 units/ml of interleukin 2 reinstated locomotor ability. Short-term exposure of any of the lymphocyte populations to interleukin 1-alpha, interleukin 1-beta, interleukin 2, interleukin 3, interleukin 4, alpha-interferon, or gamma-interferon had no effect on migration. Thus, TIL display a uniquely arrested ability to locomote through collagen gel. Inhibition of the locomotion of infiltrating effector cells is possibly a mechanism by which the tumor evades the host immune system.

Antigens, CD↗
PubMed1985

T cell locomotion in the tumor microenvironment. I. A collagen-matrix assay.

Previous studies have shown that lymphocytic infiltrates of different mouse mammary tumors contain different proportions of the T cell subsets Lyt-1+ and Lyt-2+. These characteristic subset ratios may be established, at least in part, by differential locomotion of subsets in response to components of the tumor microenvironment, such as soluble chemotactic and chemokinetic factors, cell and stromal surfaces, oxygen tension, and pH. We describe a new in vitro assay for determining how such microenvironmental variables affect lymphocyte locomotion. Suspended lymph node cells, alone or mixed with other cell types, are sandwiched between two layers of type I collagen gel and bathed in culture medium. A halo of locomotory cells fans out around the flattened droplet. Locomotion requires energy and exogenous protein. After a 24-hr incubation at 37 degrees C, 10% CO2 in air, the cell density of the halo is analyzed optically and the subset ratios are characterized by immunofluorescence staining of the gel sandwich. Under standard culture conditions, the locomotory population is enriched 12% in Thy-1+ cells compared with the bulk population, and the ratio of Lyt-1+ to Lyt-2+ cells is significantly increased. Lymphocyte locomotion is inhibited by 1 microM PGE2, by decreased pH and oxygen tension, and by the presence of normal mammary cells or mammary adenocarcinoma cells. The Lyt-1+:2+ ratio in the locomotory population is not altered by PGE2 but is reduced by acidity and hypoxia. The ratio is also reduced by the presence of mammary cells and cells of one of the mammary adenocarcinoma cell lines tested (168) but not by two others (68H and 410). Our data support the hypothesis that the locomotion of T cell subsets is differentially responsive to the types of microenvironmental conditions that vary among tumors.

Animals↗
PubMed1977

The role of cellular locomotion in leukemic infiltration. An organ culture study on penetration of L 5222 rat leukemia cells into the chick embryo mesonephros.

The significance of cellular locomotion for leukemic infiltration was investigated using L 5222 rat leukemia cells. Previous cinemicrographic studies have shown that these cells are able to locomote only after formation of a uropod-like posterior extension. This characteristic locomotive configuration of L 5222 cells is easily recognizable in scanning electron micrographs and appropriate sections. Leukemia cells were inoculated on slices of chick embryo mesonephros incubated for 24h; at this time the fragments are completely encapsulated. Leukemic infiltration is found to begin within the first 2 h and to increase gradually up to the end of the observation period at 72 h. Spread of leukemia cells occurs mainly in the intertubular spaces; the tubular epithelium is only rarely affected. In all stages of infiltration, L5222 cells with the characteristic locomotive configuration are frequently recorded. Besides this strong although indirect indication for the significance of locomotion, further evidence was provided by experiments performed at 25 degrees C and 18 degrees C. In accordance with the previous cinemicrographic finding that at these temperatures L 5222 cells are unable to produce their posterior extension, no leukemic infiltration mesonephros fragments is recognizable at subnormal temperatures.

Animals↗
PubMed1985

Coupling of cytoskeleton functions for fibroblast locomotion.

Using a chick cell phenotype specialised for locomotion with morphometric measurements made possible by modern instrumentation technology, we have reinvestigated motile functions in fibroblast locomotion. Quantitative analysis of rapid fluctuations in cell form and organelle distribution during locomotion showed many significant correlations between different parts of the cell despite much irregularity in individual displacements over the time scale of the order of one second. These broke down when external perturbations caused changes in shape or direction. Partial energy deprivation caused the cells to lose control of shape and organelle distribution even though forward protrusion continued unaffected. Cytoplasmic displacements shown by marker mitochondria correlated with adjacent fluctuations at the leading edge, and drug treatments which increased the amplitude of mitochondrial movements caused visible protrusions in projected positions at the leading edge. We conclude that fibroblast locomotion may be driven coordinately by a common set of motility mechanisms and that this coordination may be lost as a result of physical or pharmacological disturbance. Taking our evidence with results from other Laboratories, we propose the following cytoskeleton functions. (i) Protrusive activity, probably based on solation--gelation cycles of the actin based cytoskeleton and membrane recycling which provides cellular and membrane components for streaming through the cell body to the leading edge; this is Ca++ sensitive but relatively energy insensitive. (ii) Constraining activity on the cell membrane and on certain organelles to maintain shape and so facilitate directionality and the drawing along of the trailing body; this is Ca++ insensitive but relatively energy sensitive. (iii) Channeling function of microtubules to direct the flow towards multiple foci on the leading edge, and so determine cell polarity. Such a mechanism of locomotion for fibroblasts has many features consistent with evidence for other cell types, especially amoebae and leukocytes.

Animals↗
PubMed1980

The ionic basis of chemotaxis. Separate cation requirements for neutrophil orientation and locomotion in a gradient of chemotactic peptide.

The behavior of cells undergoing chemotaxis may be analyzed in terms of their orientation, a static characteristic, and of their locomotion. We have examined the extracellular divalent cation requirements for orientation and locomotion of rabbit polymorphonuclear leukocytes (neutrophils) in a gradient of the chemotactic peptide N-formyl-methionyl-leu-cyl-phenylalanine (F-Met-Leu-Phe) using the chemotaxis chamber recently developed by Zigmond. This chamber allows direct observation of cells attached to glass coverslips as they move up a gradient of chemotactic agent established across a 1-mm bridge. The orientation of neutrophils in the direction of the gradient was equally efficient whether cells and F-Met-Leu-Phe were suspended in merium supplemented with both Ca2+ and Mg2+ (complete medium), with Mg2+ but not Ca2+ (by simple omission of Ca2+ or by addition of EGTA), or with nonsupplemented medium (by omission of Ca2+ and Mg2+ or by addition of EDTA). These data confirm and extend Zigmond's earlier observation that exogenous divalent cations are not required for polymorphonuclear leukocyte orientation toward the chemotactic peptide. In contrast, cell locomotion, determined by linking the chemotaxis chamber to a time-lapse videocassette recorder and TV monitor, is markedly affected by the medium's content of divalent cations. Cells suspended in medium supplemented with Mg2+ but not calcium (by omission or chelation) or in nonsupplemented medium moved on the average 25% more rapidly than cells in complete Ca2+ and Mg2+ medium. Although the simple omission of Mg2+ does not prevent chemotaxis, chelation of Mg2+ in the medium completely abolishes leukocyte locomotion. Addition of varying concentrations of Mg2+ to the buffer in the presence of EDTA established that cell movement is fully restored by Mg2+ concentrations in the range of 3 X 10(-9) M, concentrations easily attained in the absence of added Mg2+. It was concluded that neither Ca2+ nor Mg2+ is needed for orientation in response to F-Met-Leu-Phe. However, low levels of exogenous Mg2+ but not Ca2+ are required for effective locomotion of neutrophils in the Zigmond changer. This result contrasts with data obtained in the Boyden chamber, where exogenous Ca2+ is considered essential for maximum chemotactic response.

Animals↗