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Schmidt CF, Harer WB. THE ACTION OF DRUGS ON RESPIRATION : II. ETHER, CHLOROFORM, CHLORAL, URETHANE, LUMINAL, MAGNESIUM, CAFFEINE, STRYCHNINE, AND ATROPINE. ACTA ACUST UNITED AC 2010; 37:69-81. [PMID: 19868714 PMCID: PMC2128405 DOI: 10.1084/jem.37.1.69] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
1. The depressant drugs which have been studied in this series of experiments were found to resemble morphine and heroine in that they depressed expiration more than inspiration, but they acted only in narcotic doses and always depressed inspiration at the same time. Ether caused a sharp expiratory rhythm, persisting until narcosis was very deep, probably a result of irritation of the air passages. Chloroform sometimes caused dyspnea, even in very deep narcosis, probably because of circulatory depression. Hydrated chloral made respiration more rapid, but shallower. Urethane usually made expiration active, often with inspiratory pauses, such as may follow vagotomy. Magnesium seemed to produce the most uniform, uncomplicated depression of all the depressants tried. Luminal resembled morphine and heroine more closely than any of the general depressants, making expiration passive without depressing inspiration, but it acted only in narcotic doses, unlike morphine and heroine. 2. Caffeine and strychnine, whenever they caused acceleration after morphine, brought back active expiration. Atropine never stimulated, and commonly acted as a synergist to morphine. 3. It is suggested that the results outlined in this and the preceding paper point to the existence of a separate central mechanism for the control of each of the phases of respiration, and that, while each responds to the same chemical stimuli, the threshold of the expiratory is higher than that of the inspiratory. Evidence is presented to indicate that if expiration remains passive a marked increase in depth of breathing may slow the rate, and a respiratory mechanism that lacks active expiration may be so inefficient that a CO2 concentration which stimulated when expiration was active may depress when it is passive.
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Lakämper S, Thiede C, Düselder A, Reiter S, Korneev MJ, Kapitein LC, Peterman EJG, Schmidt CF. The effect of monastrol on the processive motility of a dimeric kinesin-5 head/kinesin-1 stalk chimera. J Mol Biol 2010; 399:1-8. [PMID: 20227420 DOI: 10.1016/j.jmb.2010.03.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Revised: 02/26/2010] [Accepted: 03/03/2010] [Indexed: 12/24/2022]
Abstract
Controlled activity of several kinesin motors is required for the proper assembly of the mitotic spindle. Eg5, a homotetrameric bipolar kinesin-5 from Xenopus laevis, can cross-link and slide anti-parallel microtubules apart by a motility mechanism comprising diffusional and directional modes. How this mechanism is regulated, possibly by the tail domains of the opposing motors, is poorly understood. In order to explore the basic unregulated kinesin-5 motor activity, we generated a stably dimeric kinesin-5 construct, Eg5Kin, consisting of the motor domain and neck linker of Eg5 and the neck coiled coil of Drosophila melanogaster kinesin-1 (DmKHC). In single-molecule motility assays, we found this chimera to be highly processive. In addition, we studied the effect of the kinesin-5-specific inhibitor monastrol using single-molecule fluorescence assays. We found that monastrol reduced the length of processive runs, but strikingly did not affect velocity. Quantitative analysis of monastrol dose dependence suggests that two bound monastrol molecules are required to be bound to an Eg5Kin dimer to terminate a run.
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MacKintosh FC, Schmidt CF. Active cellular materials. Curr Opin Cell Biol 2010; 22:29-35. [DOI: 10.1016/j.ceb.2010.01.002] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 12/27/2009] [Accepted: 01/04/2010] [Indexed: 02/02/2023]
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Calmat S, Hendriks J, van Heerikhuizen H, Schmidt CF, van der Vies SM, Peterman EJG. Dissociation kinetics of the GroEL-gp31 chaperonin complex studied with Förster resonance energy transfer. Biochemistry 2010; 48:11692-8. [PMID: 19899806 DOI: 10.1021/bi9013962] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Propagation of bacteriophage T4 in its host Escherichia coli involves the folding of the major capsid protein gp23, which is facilitated by a hybrid chaperone complex consisting of the bacterial chaperonin GroEL and the phage-encoded co-chaperonin, gp31. It has been well established that the GroEL-gp31 complex is capable of folding gp23 whereas the homologous GroEL-GroES complex cannot perform this function. To assess whether this is a consequence of differences in the interactions of the proteins within the chaperonin complex, we have investigated the dissociation kinetics of GroEL-gp31 and GroEL-GroES complexes using Forster resonance energy transfer. Here we report that the dissociation of gp31 from GroEL is slightly faster than that of GroES from GroEL and is further accelerated by the binding of gp23. In contrast to what had been observed previously, we found that gp23 is able to interact with the GroEL-GroES complex, which might explain how bacteriophage T4 redirects the folding machinery of Escherichia coli during morphogenesis.
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van Mameren J, Vermeulen KC, Gittes F, Schmidt CF. Leveraging single protein polymers to measure flexural rigidity. J Phys Chem B 2009; 113:3837-44. [PMID: 19673071 DOI: 10.1021/jp808328a] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The micrometer-scale length of some protein polymers allows them to be mechanically manipulated in single-molecule experiments. This provides a direct way to measure persistence length. We have used a double optical trap to elastically deform single microtubules and actin filaments. Axial extensional force was exerted on beads attached laterally to the filaments. Because the attachments are off the line of force, pulling the beads apart couples to local bending of the filament. We present a simple mechanical model for the resulting highly nonlinear elastic response of the dumbbell construct. The flexural rigidities of the microfilaments that were found by fitting the model to the experimentally observed force-distance curves are (7.1 +/- 0.8) x 10(4) pN nm2 (persistence length L(p) = 17.2 microm) for F-actin and (6.1 +/- 1.3) x 10(6) pN nm2 (L(p) = 1.4 mm) for microtubules.
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Nijenhuis N, Mizuno D, Spaan JAE, Schmidt CF. Viscoelastic response of a model endothelial glycocalyx. Phys Biol 2009; 6:025014. [PMID: 19571362 DOI: 10.1088/1478-3975/6/2/025014] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Many cells cover themselves with a multifunctional polymer coat, the pericellular matrix (PCM), to mediate mechanical interactions with the environment. A particular PCM, the endothelial glycocalyx (EG), is formed by vascular endothelial cells at their luminal side, forming a mechanical interface between the flowing blood and the endothelial cell layer. The glycosaminoglycan (GAG) hyaluronan (HA) is involved in the main functions of the EG, mechanotransduction of fluid shear stress and molecular sieving. HA, due to its length, is the only GAG in the EG or any other PCM able to form an entangled network. The mechanical functions of the EG are, however, impaired when any one of its components is removed. We here used microrheology to measure the effect of the EG constituents heparan sulfate, chondroitin sulfate, whole blood plasma and albumin on the high-bandwidth mechanical properties of a HA solution. Furthermore, we probed the effect of the hyaldherin aggrecan, a constituent of the PCM of chondrocytes, and very similar to versican (present in the PCM of various cells, and possibly in the EG). We show that components directly interacting with HA (chondroitin sulfate and aggrecan) can increase the viscoelastic shear modulus of the polymer composite.
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Mizuno D, Bacabac R, Tardin C, Head D, Schmidt CF. High-resolution probing of cellular force transmission. PHYSICAL REVIEW LETTERS 2009; 102:168102. [PMID: 19518758 DOI: 10.1103/physrevlett.102.168102] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2008] [Indexed: 05/27/2023]
Abstract
Cells actively probe mechanical properties of their environment by exerting internally generated forces. The response they encounter profoundly affects their behavior. Here we measure in a simple geometry the forces a cell exerts suspended by two optical traps. Our assay quantifies both the overall force and the fraction of that force transmitted to the environment. Mimicking environments of varying stiffness by adjusting the strength of the traps, we found that the force transmission is highly dependent on external compliance. This suggests a calibration mechanism for cellular mechanosensing.
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Calmat S, Heerikhuizen H, Schmidt CF, Peterman EJ, Vies SM. Unravelling the chaperonin‐assisted folding of the bacteriophage T4 major capsid protein. FASEB J 2009. [DOI: 10.1096/fasebj.23.1_supplement.lb214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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60
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van den Wildenberg SMJL, Tao L, Kapitein LC, Schmidt CF, Scholey JM, Peterman EJG. The homotetrameric kinesin-5 KLP61F preferentially crosslinks microtubules into antiparallel orientations. Curr Biol 2009; 18:1860-4. [PMID: 19062285 DOI: 10.1016/j.cub.2008.10.026] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 10/06/2008] [Accepted: 10/08/2008] [Indexed: 01/15/2023]
Abstract
The segregation of genetic material during mitosis is coordinated by the mitotic spindle, whose action depends upon the polarity patterns of its microtubules (MTs). Homotetrameric mitotic kinesin-5 motors can crosslink and slide adjacent spindle MTs, but it is unknown whether they or other motors contribute to establishing these MT polarity patterns. Here, we explored whether the Drosophila embryo kinesin-5 KLP61F, which plausibly crosslinks both parallel and antiparallel MTs, displays a preference for parallel or antiparallel MT orientation. In motility assays, KLP61F was observed to crosslink and slide adjacent MTs, as predicted. Remarkably, KLP61F displayed a 3-fold higher preference for crosslinking MTs in the antiparallel orientation. This polarity preference was observed in the presence of ADP or ATP plus AMPPNP, but not AMPPNP alone, which induces instantaneous rigor binding. Also, a purified motorless tetramer containing the C-terminal tail domains displayed an antiparallel orientation preference, confirming that motor activity is not required. The results suggest that, during morphogenesis of the Drosophila embryo mitotic spindle, KLP61F's crosslinking and sliding activities could facilitate the gradual accumulation of KLP61F within antiparallel interpolar MTs at the equator, where the motor could generate force to drive poleward flux and pole-pole separation.
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61
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Nijenhuis N, Mizuno D, Spaan JA, Schmidt CF. Microrheology of the pericellular matrix. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.2694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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62
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van den Wildenberg SM, Tao L, Kapitein LC, Schmidt CF, Scholey JM, Peterman EJ. The Homotetrameric Kinesin-5, KLP61F, Preferentially Crosslinks Antiparallel Microtubules. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.2618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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63
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Ivanovska IL, de Pablo PJ, Miranda R, Gibbons MM, Michel JP, Wuite GJ, MacKintosh FC, Carrascosa JL, Klug WS, Bruinsma RF, Knobler CM, Schmidt CF. Response of Viral Shells under Nano-Indentation. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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64
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Jabbari-Farouji S, Atakhorrami M, Mizuno D, Eiser E, Wegdam GH, Mackintosh FC, Bonn D, Schmidt CF. High-bandwidth viscoelastic properties of aging colloidal glasses and gels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:061402. [PMID: 19256836 DOI: 10.1103/physreve.78.061402] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2007] [Indexed: 05/27/2023]
Abstract
We report measurements of the frequency-dependent shear moduli of aging colloidal systems that evolve from a purely low-viscosity liquid to a predominantly elastic glass or gel. Using microrheology, we measure the local complex shear modulus G;{*}(omega) over a very wide range of frequencies (from 1Hzto100kHz ). The combined use of one- and two-particle microrheology allows us to differentiate between colloidal glasses and gels-the glass is homogenous, whereas the colloidal gel shows a considerable degree of heterogeneity on length scales larger than 0.5microm . Despite this characteristic difference, both systems exhibit similar rheological behaviors which evolve in time with aging, showing a crossover from a single-power-law frequency dependence of the viscoelastic modulus to a sum of two power laws. The crossover occurs at a time t_{0} , which defines a mechanical transition point. We found that the data acquired during the aging of different samples can be collapsed onto a single master curve by scaling the aging time with t_{0} . This raises questions about the prior interpretation of two power laws in terms of a superposition of an elastic network embedded in a viscoelastic background.
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Kapitein LC, Janson ME, van den Wildenberg SM, Hoogenraad CC, Schmidt CF, Peterman EJ. Microtubule-Driven Multimerization Recruits ase1p onto Overlapping Microtubules. Curr Biol 2008; 18:1713-7. [DOI: 10.1016/j.cub.2008.09.046] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2007] [Revised: 09/15/2008] [Accepted: 09/15/2008] [Indexed: 11/16/2022]
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66
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Nijenhuis N, Mizuno D, Schmidt CF, Vink H, Spaan JAE. Microrheology of Hyaluronan Solutions: Implications for the Endothelial Glycocalyx. Biomacromolecules 2008; 9:2390-8. [DOI: 10.1021/bm800381z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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67
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Kapitein LC, Kwok BH, Weinger JS, Schmidt CF, Kapoor TM, Peterman EJG. Microtubule cross-linking triggers the directional motility of kinesin-5. ACTA ACUST UNITED AC 2008; 182:421-8. [PMID: 18678707 PMCID: PMC2500128 DOI: 10.1083/jcb.200801145] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Although assembly of the mitotic spindle is known to be a precisely controlled process, regulation of the key motor proteins involved remains poorly understood. In eukaryotes, homotetrameric kinesin-5 motors are required for bipolar spindle formation. Eg5, the vertebrate kinesin-5, has two modes of motion: an adenosine triphosphate (ATP)–dependent directional mode and a diffusive mode that does not require ATP hydrolysis. We use single-molecule experiments to examine how the switching between these modes is controlled. We find that Eg5 diffuses along individual microtubules without detectable directional bias at close to physiological ionic strength. Eg5's motility becomes directional when bound between two microtubules. Such activation through binding cargo, which, for Eg5, is a second microtubule, is analogous to known mechanisms for other kinesins. In the spindle, this might allow Eg5 to diffuse on single microtubules without hydrolyzing ATP until the motor is activated by binding to another microtubule. This mechanism would increase energy and filament cross-linking efficiency.
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Bacabac RG, Mizuno D, Schmidt CF, MacKintosh FC, Van Loon JJ, Klein-Nulend J, Smit TH. Erratum to “Round versus flat: Bone cell morphology, elasticity, and mechanosensing” [J. Biomech. 41 (2008) 1590–1598]. J Biomech 2008. [DOI: 10.1016/j.jbiomech.2008.01.035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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69
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Walder R, Schmidt CF, Dennin M. Combined macro- and microrheometer for use with Langmuir monolayers. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2008; 79:063905. [PMID: 18601415 DOI: 10.1063/1.2937649] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A Langmuir monolayer trough that is equipped for simultaneous microrheology and standard rheology measurements has been constructed. The central elements are the trough itself with a full range of optical tools accessing the air-water interface from below the trough and a portable knife-edge torsion pendulum that can access the interface from above. The ability to simultaneously measure the mechanical response of Langmuir monolayers on very different length scales is an important step for our understanding of the mechanical response of two-dimensional viscoelastic networks.
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70
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Atakhorrami M, Mizuno D, Koenderink GH, Liverpool TB, MacKintosh FC, Schmidt CF. Short-time inertial response of viscoelastic fluids measured with Brownian motion and with active probes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:061508. [PMID: 18643273 DOI: 10.1103/physreve.77.061508] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Revised: 04/27/2008] [Indexed: 05/26/2023]
Abstract
We have directly observed short-time stress propagation in viscoelastic fluids using two optically trapped particles and a fast interferometric particle-tracking technique. We have done this both by recording correlations in the thermal motion of the particles and by measuring the response of one particle to the actively oscillated second particle. Both methods detect the vortexlike flow patterns associated with stress propagation in fluids. This inertial vortex flow propagates diffusively for simple liquids, while for viscoelastic solutions the pattern spreads superdiffusively, depending on the shear modulus of the medium.
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71
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Bacabac RG, Mizuno D, Schmidt CF, MacKintosh FC, Van Loon JJWA, Klein-Nulend J, Smit TH. Round versus flat: bone cell morphology, elasticity, and mechanosensing. J Biomech 2008; 41:1590-8. [PMID: 18402963 DOI: 10.1016/j.jbiomech.2008.01.031] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2006] [Revised: 11/11/2007] [Accepted: 01/24/2008] [Indexed: 01/16/2023]
Abstract
There is increasing evidence that cell function and mechanical properties are closely related to morphology. However, most in vitro studies investigate flat adherent cells, which might not reflect physiological geometries in vivo. Osteocytes, the mechanosensors in bone, reside within ellipsoid containment, while osteoblasts adhere to flatter bone surfaces. It is unknown whether morphology difference, dictated by the geometry of attachment is important for cell rheology and mechanosensing. We developed a novel methodology for investigating the rheology and mechanosensitivity of bone cells under different morphologies using atomic force microscopy and our two-particle assay for optical tweezers. We found that the elastic constant of MLO-Y4 osteocytes when flat and adherent (>1 kPa) largely differed when round but partially adherent (<1 kPa). The elastic constant of round suspended MLO-Y4 osteocytes, MC3T3-E1 osteoblasts, and primary osteoblasts were similarly <1 kPa. The mechanosensitivity of round suspended MLO-Y4 osteocytes was investigated by monitoring nitric oxide (NO) release, an essential signaling molecule in bone. A preliminary observation of high NO release from round suspended MLO-Y4 osteocytes in response to approximately 5 pN force is reported here, in contrast with previous studies where flat cells routinely release lesser NO while being stimulated with higher force. Our results suggest that a round cellular morphology supports a less stiff cytoskeleton configuration compared with flat cellular morphology. This implies that osteocytes take advantage of their ellipsoid morphology in vivo to sense small strains benefiting bone health. Our assay provides novel opportunities for in vitro studies under a controlled suspended morphology versus commonly studied adherent morphologies.
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72
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Atakhorrami M, Addas KM, Schmidt CF. Twin optical traps for two-particle cross-correlation measurements: eliminating cross-talk. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2008; 79:043103. [PMID: 18447519 DOI: 10.1063/1.2898407] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The correlated motions of two micron-sized particles reflect the (micro-) rheological properties of a fluid and can be conveniently detected using two optical traps in combination with interferometric displacement detection. When the correlations become small, cross-talk between the two beams becomes important. We have used dual optical traps created by either two orthogonally polarized laser beams derived from one laser source, or by two independent lasers of different wavelengths for microrheology experiments. High numerical aperture lenses (objective and condenser) in the optical path can introduce depolarization, and polarizing beam splitters are not perfect, both of which can lead to optical cross-talk. We have characterized the cross-talk in our setup and demonstrate that the use of two independent laser eliminates cross-talk entirely.
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73
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Calmat S, Hendriks J, Heerikhuizen H, Schmidt CF, Vies SM, Peterman EJ. The dynamics of the GroEL‐gp31 chaperonin complex studied with fluorescence spectroscopy. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.1001.5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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74
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Jabbari-Farouji S, Mizuno D, Atakhorrami M, MacKintosh FC, Schmidt CF, Eiser E, Wegdam GH, Bonn D. Fluctuation-dissipation theorem in an aging colloidal glass. PHYSICAL REVIEW LETTERS 2007; 98:108302. [PMID: 17358575 DOI: 10.1103/physrevlett.98.108302] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2005] [Indexed: 05/14/2023]
Abstract
We provide a direct experimental test of the fluctuation-dissipation theorem (FDT) in an aging colloidal glass. The use of combined active and passive microrheology allows us to independently measure both the correlation and response functions in this nonequilibrium situation. Contrary to previous reports, we find no deviations from the FDT over several decades in frequency (1 Hz-10 kHz) and for all aging times. In addition, we find two distinct viscoelastic contributions in the aging glass, including a nearly elastic response at low frequencies that grows during aging.
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75
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Korneev MJ, Lakämper S, Schmidt CF. Load-dependent release limits the processive stepping of the tetrameric Eg5 motor. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:675-81. [PMID: 17333163 PMCID: PMC1914257 DOI: 10.1007/s00249-007-0134-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/27/2006] [Revised: 12/20/2006] [Accepted: 01/02/2007] [Indexed: 12/02/2022]
Abstract
Tetrameric motor proteins of the Kinesin-5 family are essential for eukaryotic cell division. The microscopic mechanism by which Eg5, the vertebrate Kinesin-5, drives bipolar mitotic spindle formation remains unknown. Here we show in optical trapping experiments that full-length Eg5 moves processively and stepwise along microtubule bundles. Interestingly, the force produced by individual Eg5 motors typically reached only ∼2 pN, one-third of the stall force of Kinesin-1. Eg5 typically detached from microtubules before stalling. This behavior may reflect a regulatory mechanism important for the role of Eg5 in the mitotic spindle.
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