Contraction Of Cell Body Research Articles

The fibrous character of pericellular matrix mediates cell mechanotransduction

Cells in solid tissues sense and respond to mechanical signals that are transmitted through extracellular matrix (ECM) over distances that are many times their size. This long-range force transmission is known to arise from strain-stiffening and buckling in the collagen fiber ECM network, but must also pass through the denser pericellular matrix (PCM) that cells form by secreting and compacting nearby collagen. However, the role of the PCM in the transmission of mechanical signals is still unclear. We therefore studied an idealized computational model of cells embedded within fibrous collagen ECM and PCM. Our results suggest that the smaller network pore sizes associated with PCM attenuates tension-driven collagen-fiber alignment, undermining long-range force transmission and shielding cells from mechanical stress. However, elongation of the cell body or anisotropic cell contraction can compensate for these effects to enable long distance force transmission. Results are consistent with recent experiments that highlight an effect of PCM on shielding cells from high stresses. Results have implications for the transmission of mechanical signaling in development, wound healing, and fibrosis.

Protective effect and mechanisms of umbilical cord tissue transplantation on radiation-induced learning and memory impairment in rats

Objective To investigate the protective effect and mechanisms of umbilical cord tissue transplantation on radiation-induced learning and memory impairment in rats. Methods Sixty SD rats were randomly divided into three groups with 20 in each group: control group, model group (whole brain X-ray irradiation, dose 20 Gy) and treatment group (whole brain X-ray irradiation, dose 20 Gy + umbilical cord tissue transplantation). The changes of body mass were observed, and the learning and memory of rats were observed by water maze test on the 14th and 28th day after irradiation, the neuron state of hippocampus was observed by HE staining, and the expressions of NF-κB pathway related proteins and IL-6 in hippocampus were detected by Western blot.Descriptive analysis and hypothesis testing were processed by SPSS 17.0. Results (1) On the 28th day, the escaping latency in the water maze experiment of the treatment group was significantly higher than that of the control group and lower than that of the model group (control group: (11.77±3.02) s, model group: (23.75±3.27)s, treatment group: (18.49±2.32)s; t=3.940, -2.943, both P<0.05); the number of crossing platform in the treatment group was significantly lower than that in the control group and higher than that in the model group (control group: (7.20±0.84), model group (3.60±1.14 ), treatment group (5.00±1.00); t=-3.773, 2.064, both P<0.05). (2)HE staining showed that the neurons in the control group were arranged orderly and the cytoplasm was transparent.The neurons in the model group were arranged disorderly and the contraction of the cell body was triangular or irregular.The number of neurons in the treatment group was less than that in the model group. (3) On the 14th day, the relative expression of TLR4 in the treatment group was significantly higher than that in the control group and lower than that in the model group (control group: (0.69±0.03), model group: (1.06±0.11), treatment group: (0.90±0.04); t=7.275, -2.368, both P<0.05). The relative expression of NF-κB p65 in the treatment group was significantly higher than that in the control group and lower than that in the model group (control group: (1.67±0.12), model group: (2.08 ±0.06), treatment group: (1.93±0.08); t=3.236, -2.684, both P<0.05). The relative expression of IL-6 in the treatment group was significantly higher than that in the control group and lower than that in the model group (control group: (0.77±0.08), model group: (1.12±0.07), treatment group: (0.95±0.06); t=3.274, -3.495, both P<0.05). The relative expression of Bcl-2 / Bax in the treatment group was significantly lower than that in the control group and higher than that in the model group (control group: (1.40±0.52), model group: (0.48±0.06), treatment group: (0.72±0.0 3); t=-2.263, 6.350, both P<0.05). The expression trend of IL-6 and Bcl-2 / Bax protein on the 28th day was the same as that on the 14th day. Conclusion Cord tissue transplantation can improve the learning and memory impairment caused by radiotherapy, which may be related with the inhibition of inflammation caused by radiotherapy. Key words: Umbilical cord; Umbilical cord mesenchymal stem cells; Radiation therapy; Inflammation; Learning and memory

Synaptic Plasticity of Human Umbilical Cord Mesenchymal Stem Cell Differentiating into Neuron-like Cells In Vitro Induced by Edaravone.

Objective The human umbilical cord mesenchymal stem cells (hUMSCs) are characterized with the potential ability to differentiate to several types of cells. Edaravone has been demonstrated to prevent the hUMSCs from the oxidative damage, especially its ability in antioxidative stress. We hypothesized that Edaravone induces the hUMSCs into the neuron-like cells. Methods The hUMSCs were obtained from the human umbilical cord tissue. The differentiation of hUMSCs was induced by Edaravone with three different doses: 0.65 mg/ml, 1.31 mg/ml, and 2.62 mg/ml. Flow cytometry was used to detect the cell markers. Protein and mRNA levels of nestin, neuron-specific enolase (NSE), and glial fibrillary acidic protein (GFAP) were detected by Western blot and RT-PCR. The expression of synaptophysin (SYN), growth-associated protein 43 (GAP43), and postsynaptic density 95 (PSD95) was detected by Real-Time PCR. Results As long as the prolongation of the culture, the hUMSCs displayed with the long strips or long fusiform to fat and then characterized with the radial helix growth. By using flow cytometry, the cultured hUMSCs at the 3rd, 5th, and 10th passages were expressed with CD73, CD90, and CD105 but not CD11b, CD19, CD34, CD45, and HLA-DR. Most of the hUMSCs cultured with Edaravone exhibited typical nerve-immediately characters including the cell body contraction, increased refraction, and protruding one or more elongated protrusions, which were not found in the control group without addition of Edaravone. NSE, nestin, and GFAP were positive in these neuron-like cells. Edaravone dose-dependently increased expression levels of NSE, nestin, and GFAP. After replacement of maintenance fluid, neuron-like cells continued to be cultured for five days. These neuron-like cells were positive for SYN, PSD95, and GAP43. Conclusion Edaravone can dose-dependently induce hUMSCs to differentiate into neuron-like cells that expressed the neuronal markers including NSE, nestin, and GFAP and synaptic makers such as SYN, PSD95, and GAP43.

Calpain-mediated integrin deregulation as a novel mode of action for the anticancer gallium compound KP46.

On the basis of enhanced tumor accumulation and bone affinity, gallium compounds are under development as anticancer and antimetastatic agents. In this study, we analyzed molecular targets of one of the lead anticancer gallium complexes [KP46, Tris(8-quinolinolato)gallium(III)] focusing on colon and lung cancer. Within a few hours, KP46 treatment at low micromolar concentrations induced cell body contraction and loss of adhesion followed by prompt cell decomposition. This rapid KP46-induced cell death lacked classic apoptotic features and was insensitive toward a pan-caspase inhibitor. Surprisingly, however, it was accompanied by upregulation of proapoptotic Bcl-2 family members. Furthermore, a Bax- but not a p53-knockout HCT-116 subline exhibited significant KP46 resistance. Rapid KP46-induced detachment was accompanied by downregulation of focal adhesion proteins, including several integrin subunits. Loss of integrin-β1 and talin plasma membrane localization corresponded to reduced binding of RGD (Arg-Gly-Asp) peptides to KP46-treated cells. Accordingly, KP46-induced cell death and destabilization of integrins were enhanced by culture on collagen type I, a major integrin ligand. In contrast, KP46-mediated adhesion defects were partially rescued by Mg(2+) ions, promoting integrin-mediated cell adhesion. Focal adhesion dynamics are regulated by calpains via cleavage of multiple cell adhesion molecules. Cotreatment with the cell-permeable calpain inhibitor PD150606 diminished KP46-mediated integrin destabilization and rapid cell death induction. KP46 treatment distinctly inhibited HCT-116 colon cancer xenograft in vivo by causing reduced integrin plasma membrane localization, tissue disintegration, and intense tumor necrosis. This study identifies integrin deregulation via a calpain-mediated mechanism as a novel mode of action for the anticancer gallium compound KP46.

Three-dimensional cell body shape dictates the onset of traction force generation and growth of focal adhesions.

Cell shape affects proliferation and differentiation, which are processes known to depend on integrin-based focal adhesion (FA) signaling. Because shape results from force balance and FAs are mechanosensitive complexes transmitting tension from the cell structure to its mechanical environment, we investigated the interplay between 3D cell shape, traction forces generated through the cell body, and FA growth during early spreading. Combining measurements of cell-scale normal traction forces with FA monitoring, we show that the cell body contact angle controls the onset of force generation and, subsequently, the initiation of FA growth at the leading edge of the lamella. This suggests that, when the cell body switches from convex to concave, tension in the apical cortex is transmitted to the lamella where force-sensitive FAs start to grow. Along this line, increasing the stiffness resisting cell body contraction led to a decrease of the lag time between force generation and FA growth, indicating mechanical continuity of the cell structure and force transmission from the cell body to the leading edge. Remarkably, the overall normal force per unit area of FA increased with stiffness, and its values were similar to those reported for local tangential forces acting on individual FAs. These results reveal how the 3D cell shape feeds back on its internal organization and how it may control cell fate through FA-based signaling.

MIF inhibits monocytic movement through a non-canonical receptor and disruption of temporal Rho GTPase activities in U-937 cells

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine that was initially identified by its ability to inhibit the movement of macrophages. Cell migration is a highly complex process involving changes to the cytoskeleton and cell adhesion molecules, and is regulated by the Rho GTPases. A simple model using human monocytic U-937 cells to elicit the classic MIF response was implemented to examine the mechanism of MIF-induced migration inhibition. Our results demonstrate that MIF inhibits migration of these U-937 cells through a non-canonical receptor, CXCR4, in the absence of the putative primary MIF receptor CD74. Migration inhibition is dependent upon a series of temporal perturbations of the activities of the Rho GTPases: initial activation followed by subsequent inactivation of RhoA, inactivation of Rac1, and cyclic activation of Cdc42. MIF-mediated changes in the activities of the Rho GTPases jointly contributed to migration inhibition in these cells. Collectively, these data suggest that the MIF-mediated migration inhibition is mediated by the outcome of G-protein signaling, and in less adherent cells such as those of the monocyte/macrophage lineage, RhoA directly affects net translocation through its ability to induce cell body contraction. These findings demonstrate that CXCR4 can mediate MIF signaling in the absence of CD74 in addition to serving as a MIF co-receptor along with CD74. These results correlate MIF activity to specific and sequential Rho GTPase activity perturbations, and given that CXCR4 functions in numerous processes, suggests potential roles for the modulation of cell movement in those events including development, cell survival and viral infection.

Abstract 3445: Targeting Thromboxane A2 receptor (TP) to block breast cancer metastasis

Abstract The thromboxane A2 (TXA2) receptor, TP, is a G-protein coupled receptor. Previous studies in our lab have shown that the TP pathway regulates tumor cell cytoskeleton and TP activation induces rapid tumor cell contractions through small GTPase RhoA activation. Conversely, TP depletion reduces the metastatic dissemination of breast cancer cells in vivo by blocking the extravasation of tumor cells. Humans express two TP isoforms, TPγ and TPα. We report here that elevated TPγ expression is associated with metastasis in patients with breast cancer. While TPγ is expressed in all breast cancer cell lines that we examined, TPγ is only expressed in malignant cell lines, indicates that TPγ plays a role in breast cancer progression. Treatment with a selective TPγ inhibitor (CAY10535) blocks TP agonist (U46619) induced cell body contraction and RhoA activation. Additionally, TPγ inhibitor reduces migratory capacity and invasiveness in human breast cancer cell lines. Our previous work has shown that active TP is required for efficient extravasation of tumor cells in vivo; in this study, we further demonstrate that mice treated with SQ29548 (a high affinity TP antagonist) prior to tumor cell injection developed fewer metastatic lesions than the mice treated with SQ29548 after tumor cell injection. In all, our study indicated that TPγ can be targeted to reduce the risk of breast cancer metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3445. doi:1538-7445.AM2012-3445

Abstract C45: Validation of thromboxane A2 receptor (TP) as a target to block breast cancer metastasis.

Abstract The receptor of thromboxane A2 (TXA2), TP, is a seven transmembrane, G-protein-coupled receptor. Increased expression of TP at RNA level was found to correlate with a poor prognosis in breast cancer patients but it is unknown how TP expression and activities are involved in breast cancer progression. Here we report that TP is expressed in metastatic breast cancer cells at both RNA and protein levels. Treatment of breast cancer MDA-MB-231 cells by U46619, a TP agonist, induced cell body contraction. The U46619-induced contraction was blocked by SQ29548, a high-affinity TP antagonist. Further studies found that small GTPase RhoA was activated by TP activation and that pretreatment of MDA-MB-231 cells with Y27632, a Rho kinase (ROCK) inhibitor, blocked U46619-induced cell contraction. The requirement of RhoA activation in U46619 induced cell contraction was further confirmed by the ability of dominant negative RhoA to block cell contraction induced by U46619. MDA-MB-231 cells with TP knockdown displayed a reduced percentage of contraction under the treatment of U46619 and TXA2 agonist I-BOP as well as attenuated invasion ability. When injected into mice, MDA-MB-231 cells with TP depleted did not present significant changes in primary tumor formation or growth. However, TP depletion reduced the ability of MDA-MB-231 cells to metastasize to the lung and the liver in an experimental metastasis model. We further demonstrated that TP depletion reduced the lung colonization ability of MDA-MB-231 cells by blocking active extravasation. Taken together, TP is expressed in breast cancer and that activation of TP has profound effects on tumor cell cytoskeleton and contraction through activation of RhoA. Inhibition or depletion of TP reduces the metastatic dissemination of breast cancer cells in vivo by blocking the extravasation of tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C45.

Immunolocalization of prestin in the human cochlea

AbstractObjective: Prestin is an anion-transporter-related protein highly expressed in mammalian outer hair cells (OHCs). It is associated with the OHC basolateral plasma membrane and responsible for cell body contraction, increasing cochlear sensitivity and frequency resolution. Here, we analysed the expression and distribution of prestin in the human cochlea. Study Design: Immunohistochemistry including confocal microscopy and SEM were performed on EDTA-decalcified human cochlea removed during petro-clival meningioma surgery. Results: Prestin was found to be expressed solely in OHCs. No staining was seen in IHCs. Prestin immunolabelling framed the OHCs along the sensory region of the human cochlea. Staining was most prominent in the lateral cell membrane with less expression in the sub- and peri-nuclear part of the cell. Prestin immunostaining was also detected in the OHC cytosol, presumably reflecting intracellular molecular trafficking. Conclusion: This study describes for the first time the localizat...

CAMP Inhibits Cell Migration by Interfering with Rac-induced Lamellipodium Formation

Cell migration is critical for animal development and physiological as well as pathological responses. One important step during cell migration is the formation of lamellipodia at the leading edge of migrating cells. Here we report that the second messenger cAMP inhibits the migration of mouse embryonic fibroblast cells and mouse breast tumor cells. cAMP acts downstream of the small GTPase Rac and interferes with the formation of lamellipodia. Moreover, cAMP decreases the phosphorylation of the myosin light chain at the leading edge of cells and increases the phosphorylation of the vasodilator-stimulated phosphoprotein. Together with our previous report of a positive role of another second messenger, cGMP, in lamellipodium formation, our data indicate that cAMP and cGMP play opposite roles in modulating lamellipodium formation.

Calcium regulates independently ciliary beat and cell contraction in Paramecium cells

Intracellular Ca(2+) concentration is a well-known signal regulator for various physiological activities. In many cases, Ca(2+) simultaneously regulates individual functions in single cells. How can Ca(2+) regulate these functions independently? In Paramecium cells, the contractile cytoskeletal network and cilia are located close to each other near the cell surface. Cell body contraction, ciliary reversal, and rises in ciliary beat frequency are regulated by intracellular Ca(2+) concentration. However, they are not always triggered simultaneously. We injected caged calcium into Paramecium caudatum cells and continuously applied weak ultraviolet light to the cells to slowly increase intracellular Ca(2+) concentration. The cell bodies began to contract just after the start of ultraviolet light application, and the degree of contraction increased gradually thereafter. On the other hand, cilia began to reverse 1.4s after the start of ultraviolet application and reversed completely within 100ms. Ciliary beat frequency in the reverse direction was significantly higher than in the normal direction. These results indicate that cell body contraction is regulated by Ca(2+) in a dose-dependent manner in living P. caudatum. On the other hand, ciliary reversal and rise in ciliary beat frequency are triggered by Ca(2+) in an all-or-none manner.

ErbB-2 and Met Reciprocally Regulate Cellular Signaling via Plexin-B1

Sema4D-induced activation of plexin-B1 has been reported to evoke different and sometimes opposing cellular responses. The mechanisms underlying the versatility of plexin-B1-mediated effects are not clear. Plexin-B1 can associate with the receptor tyrosine kinases ErbB-2 and Met. Here we show that Sema4D-induced activation and inactivation of RhoA require ErbB-2 and Met, respectively. In breast carcinoma cells, Sema4D can have pro- and anti-migratory effects depending on the presence of ErbB-2 and Met, and the exchange of the two receptor tyrosine kinases is sufficient to convert the cellular response to Sema4D from pro- to anti-migratory and vice versa. This work identifies a novel mechanism by which plexin-mediated signaling can be regulated and explains how Sema4D can exert different biological activities through the differential association of its receptor with ErbB-2 and Met.

Alkaloids from Prosopis juliflora leaves induce glial activation, cytotoxicity and stimulate NO production.

Prosopis juliflora is used for feeding cattle and humans. Intoxication with the plant has been reported, and is characterized by neuromuscular alterations and gliosis. Total alkaloidal extract (TAE) was obtained using acid/basic-modified extraction and was fractionated. TAE and seven alkaloidal fractions, at concentrations ranging 0.03–30 μg/ml, were tested for 24 h on astrocyte primary cultures derived from the cortex of newborn Wistar rats. The MTT test and the measure of LDH activity on the culture medium, revealed that TAE and fractions F29/30, F31/33, F32 and F34/35 were cytotoxic to astrocytes. The EC 50 values for the most toxic compounds, TAE, F31/33 and F32 were 2.87 2.82 and 3.01 μg/ml, respectively. Morphological changes and glial cells activation were investigated through Rosenfeld's staining, by immunocytochemistry for the protein OX-42, specific of activated microglia, by immunocytochemistry and western immunoblot for GFAP, the marker of reactive and mature astrocytes, and by the production of nitric oxide (NO). We observed that astrocytes exposed to 3 μg/ml TAE, F29/30 or F31/33 developed compact cell body with many processes overexpressing GFAP. Treatment with 30 μg/ml TAE and fractions, induced cytotoxicity characterized by a strong cell body contraction, very thin and long processes and condensed chromatin. We also observed that when compared with the control (±1.34%), the proportion of OX-42 positive cells was increased in cultures treated with 30 μg/ml TAE or F29/30, F31/33, F32 and F34/35, with values raging from 7.27% to 28.74%. Moreover, incubation with 3 μg/ml F32, 30 μg/ml TAE, F29/30, F31/33 or F34/35 induced accumulation of nitrite in culture medium indicating induction of NO production. Taken together these results show that TAE and fractionated alkaloids from P. juliflora act directly on glial cells, inducing activation and/or cytotoxicity, stimulating NO production, and may have an impact on neuronal damages observed on intoxicated animals.

Cross Talk between Rho GTPases Is Critical for Hematopoietic-Derived Inflammatory Processes.

Neutrophils are a critical cell in inflammatory processes by moving rapidly to tissue sites of inflammation to perform phagocytosis, cytokine and reactive oxygen species release. Members of the small Rho GTPase family, Rac1, Rac2, CDC42 and RhoA, are central regulators of cell movement via cytoskeleton rearrangement. We have previously demonstrated that the Rho family GTPase Rac2 is a critical regulator of neutrophil functions in vitro and in vivo (Roberts et al, Immunity 1999). We have also demonstrated that in response to formyl-methionyl-leucyl-phenylalanine (fMLP), the related GTPase Rac1 plays a distinct, but as yet ill-defined role in tail retraction during cell movement and cell spreading in vitro (Gu and Filippi et al, Science 2003). Here, we further demonstrate that Rac1 appears to be critical for β2-integrin mediated adhesion and migration likely via cross talk with another Rho GTPase, RhoA. Although, Rac1−/− PMNs show normal in vitro migration in response to fMLP using the Boyden chamber assay, Rac1−/− PMNs demonstrate a dramatic defect compared with WT cells in haptotaxis using transwell precoated with fibrinogen (1.3±0.3x103 vs 9.8±0.5x103). In addition, Rac1−/− PMNs displayed increased frequency in pseudopodia formation associated with lack of cell body contraction upon integrin ligation compared with WT (80% vs 40%). We noted that this phenotype closely mimics deregulation of the related Rho GTPase, RhoA. Remarkably, Rac1-deficiency leads to mislocalization of RhoA in neutrophils after integrin ligation and reintroduction of Rac1 into Rac1−/− cells completely restores the correct localization of RhoA. These data are consistent with the hypothesis that Rho GTPases interact in a time- and space-dependent manner. Because fMLP-induced PMN migration into the lung has previously been shown to be beta2-integrin dependent (Mackarel, Am. J. Respir. Cell. Mol. Biol 2000), we used a model of neutrophil associated lung inflammation induced by intratracheal (IT) injection of fMLP to address the physiological role of Rac1 in neutrophil-derived inflammatory processes in vivo,. To study the role of Rac1 specifically in bone marrow-derived cells, we reconstituted C57BL/6 mice with either wild type or Rac1Flox/Flox bone marrow cells. After Cre-mediated deletion of Rac1, reconstituted mice were treated with one dose of fMLP (20mg) IT. One day after fMLP exposure, bronchoalveolar lavage (BAL) from reconstituted animals showed complete loss of Rac1 expression and demonstrated significantly reduced numbers of migrated neutrophils in BAL compared with mice reconstituted with WT cells (3.1±0.65 vs 9.56±2, p<0.05). Importantly, 5 weeks after fMLP exposure IT, Rac1−/− recipients displayed a significant reduction in emphysematous lesions as compared with WT as assessed by morphometric measurement of alveolar spaces (57.6±7.8 vs 73.3±3.04, p<0.05), demonstrating the physiological relevance of Rac1 in neutrophil-related inflammatory responses in vivo.Taken together, these results suggest that Rac1 activity regulates b2 integrin-induced cell shape change and RhoA subcellular localization in PMNs and demonstrate the existence of physiological cross talk between Rac1 and RhoA where RhoA activity depends at least in part on Rac1. Thus, Rac1 and RhoA appear to coordinately regulate PMN migration into the lung during inflammation.

Electron microscopy of primary zoosporogenesis in Plasmodiophora brassicae

Primary zoosporogenesis in resting sporangia ofPlasmodiophora brassicae that had been incubated for 14 d in culture solution containing turnip seedlings was examined by transmission electron microscopy. A single zoospore differentiated within each sporangium, the differentiation being initiated by the emergence, of two flagella in the tight space formed by invagination of the plasma membrane within the sporangium. The differentiazing zoospore was similar in intracellular aspects to sporangia within clubroot galls. Then a deep groove formed on the zoospore cell body by further invagination of the plasma membrane. Two flagella appeared to coil around the zoospore cell body in parallel along this groove. Thereafter, the cell body lost the groove and became rounded following the protoplasmic condensation (contraction of cell body) during late development, and assumed an irregular shape at the stage of maturation. Intracellular features in, developing and mature zoospores were complicated, being characterized by electron-dense nuclei and mitochondria, microbodies, cored vesicles and various unidentified cytoplasmic vesicles and granules. A nucleolus-like region was observed only in the nucleus of the mature zoospore. A partially opened germ, pore was also seem in the sporangium containing the mature zoospore.

Photolysis of caged Ca2+ induces trichocyst discharge inParamecium caudatum

Trichocyst discharge, ciliary reversal, and cell body contraction inParamecium spp. have all been claimed to be regulated by the intracellular Ca2+ concentration ([Ca2+]i) at the cortical region of the cell. We injected caged Ca2+ intoP. caudatum cells and applied ultraviolet (UV) light to the cell for 125 ms. This did not induce trichocyst discharge but did induce both ciliary reversal and cell body contraction. A re-application of UV for 125 ms triggered trichocyst discharge. These results demonstrate that (1) trichocyst discharge and ciliary reversal and cell body contraction are controlled by [Ca2+]i and (2) the threshold of [Ca2+]i for trichocyst discharge is higher than those for the other two functions.

Cell Body Contraction of Splrostomum Does Not Involve Shortening of Inter-Kinetosomal Distance along Ciliary Lines

Abstract A heterotrichous ciliate Spirostomum is known to show characteristic rapid contraction of the cell body accompanied by twisting of ciliary lines which run longitudinally on the cell surface. The ciliary lines of Stentor, a closely related heterotrichous ciliate, are known to become shorter by themselves when the cell contracts, resulting in sliding between adjacent longitudinal microtubular sheets (LMSs) running just beneath the ciliary lines. In Spirostomum, in contrast, there is controversy over whether lengths of the ciliary lines alter or not. In this study, we examined changes of the ciliary line lengths by scanning electron microscopy, to measure the distance between the proximal ends of two neighboring cilia which are lining up along each ciliary line (inter-kinetosomal distances). We found that the inter-kinetosomal distance remained constant regardless of cell contraction and elongation, indicating that the cell body contraction of Spirostomum results from a cellular twisting motion with...

Synchrony of cell spreading and contraction force as phagocytes engulf large pathogens.

A simple micromechanical method has been used to directly measure the force of contraction in single mammalian phagocytes (blood granulocytes) during engulfment of large yeast pathogens. Both the time course of cell spreading over the yeast particle and increase in cell body contractile force were quantitated at three temperatures in the range of 23-35 degrees C. The surprising feature of the phagocyte response was that engulfment and cell body contraction occurred in a serial sequence: i.e., the phagocyte spread rapidly over the particle at a steady rate with no detectable cell body contraction; when spreading stopped, contraction force in the cell body then rose steadily to a plateau level that remained stationary until the next sequence of spreading and contraction. Both spreading and contraction exhibited abrupt start/stop kinetics. Also impressive, the cell contraction force stimulated by phagocytosis was quite large (approximately 10(-8) N)-two orders of magnitude larger than the force necessary to deform passive phagocytes to the same extent. If distributed uniformly over the cell cross section, the contraction force is equivalent to an average contractile stress of approximately 10(3) N/m2 (0.01 Atm). These physical measurements in situ set critical requirements for the mechanism of force generation in granulocytes, imply that a major increase in network cross-linking accompanies build-up in contractile force and that subsequent network dissolution is necessary for locomotion.