Now showing 1 - 3 of 3
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    Publication
    Direct detection of cell membrane slope fluctuations upon adding Latrunculin B using optical tweezers and single probe particle
    (01-01-2022)
    Roy, Srestha
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    Chakraborty, Snigdhadev
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    Muruga, Lokesh
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    Vaippuly, Rahul
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    Yadav, Vandana
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    Edwina, Privitha
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    The cell membrane has fluctuations due to thermal and athermal sources. That causes the membrane to flicker. Conventionally, only the normal (perpendicular to the membrane) fluctuations are studied and then used to ascertain the membrane properties like the bending rigidity. It is here that we introduce a different concept, namely the slope fluctuations of the cell membrane which can be modelled as a gradient of the normal fluctuations. This can be studied using a new technique where a birefringent particle placed on the membrane turns in the out of plane sense, called the pitch sense. We introduce the pitch detection technique in optical tweezers relying upon asymmetric scattering from a birefringent particle under crossed polarizers. We then go on to use this pitch detection technique to ascertain the power spectral density of membrane slope fluctuations and find it to be (frequency)-1 while the normal fluctuations yields (frequency)-5/3. We also explore a different regime where the cell is applied with the drug Latrunculin-B which inhibits actin polymerization and find the effect on membrane fluctuations. We find that even as the normal fluctuations now become (frequency)-4/3, the slope fluctuations spectrum still remains (frequency)-1, with exactly the same coefficient as the case when the drug was not applied. Thus, this presents a convenient opportunity to study the membrane parameters like bending rigidity as a function of time after applying the drug. This would be the first time the membrane bending rigidity could be studied as a function of time upon the application of Lat-B without reverting to AFM.
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    Publication
    Determination of local cell membrane slope fluctuations using the pitch rotational mode of optical tweezers
    (01-01-2020)
    Vaippully, Rahul
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    Ramanujam, Vaibavi
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    We study the normal fluctuations of an MCF-7 cell membrane and calibrate the optical trap to detect pitch motion to get information about the rocking motion of a birefringent particle. We could show both theoretically and experimentally that the Z power spectrum has a power-law behavior of (frequency)-5/3, and We find that the power spectrum of slope fluctuations is proportional to (frequency)-1. We could extract parameters like bending rigidity directly from the power spectrum fitting parameters in 5 Hz to 1 kHz range. Our method was powerful enough to identify pitch rotation for a spherical birefringent particle to a high resolution using optical tweezers.
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    Publication
    Anti-hypertensive Calcium-Blocking Drugs Induce a Change in Viscoelasticity of Mcf-7 Cancer Cells
    (15-09-2020)
    Vaibavi, S. R.
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    Vaippully, Rahul
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    In this work, we studied the effect of common calcium channel blockers (Verapamil Hydrochloride and Nifedipine, usually prescribed for cardiovascular diseases) on the viscoelastic property of both tumorigenic (MCF-7) and vascular endothelial (HUVEC) cell-line. Specifically, an optical-tweezer was used to locally "press-down" on the cell membrane. Fluctuations of optically-trapped dielectric beads attached to the cell membrane were measured to study the effect of drugs on the mechanical properties of the membrane and the cytoskeleton. We observed that MCF-7 cells exhibit a significantly higher mean squared displacement (MSD) in response to these drugs as compared to HUVEC cells, under no-compression condition. Furthermore, optically induced compression of cell-membrane induced a significant drop in MSD of MCF-7 cells, whereas HUVEC cells showed a significant rise in MSD. To further test these results, we depolymerized actin-cytoskeleton using latrunculin-B and measured fluctuations of beads on the surface of cells. Immunofluorescence imaging of the actin cytoskeleton correlates with the variation in the viscoelastic response of MCF-7 and HUVEC under the influence of these drugs. Our power-spectrum analysis at 10 Hz shows that actin-depolymerization decreased the activity of both cell types; however, cells treated with nifedipine or verapamil showed contrasting effects. Together, these results show that clinically approved calcium-ion blocking cardiovascular drugs have a significant effect on the viscoelastic properties of circulating tumor cells in the blood.