Non-equilibration of hydrostatic pressure in blebbing cells

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Original Entry by Holly McIlwee, AP225 Fall 09


Non-equilibration of hydrostatic pressure in blebbing cells, G. Charras, J. Yarrow, M. Horton, L. Mahadevan and T. Mitchison, Nature, 435, 365-69. 2005.


Blebs are large protrusions on a surface of a cell. The mechanism by which blebs occur is assigned to the separation of the plasma membrane from the cytoskelton and subsequent swelling and retraction. The process of bleb formation and retraction lasts on the order of tens of seconds, over about 10 microns of the cell surface and typically occurs during and in aid of apoptosis, cytokinesis, and cell movement.

In plant cells, cell membrane protrusions are governed by hydrostatic pressure. Current models of animal cells dictate that protrusions are governed by local regulation of actin biochemistry and therefore treat models of the cytoskeleton as a incompressible, viscoelastic species. The problem with this assumption is that this assumes the hydrostatic pressure equilibrates immediately across the entire cell. The author of this manuscript expresses unease with this assumption and sets out herein to create a model for non-equilibrium hydrostatic pressure to explain the blebbing phenomena.


Cell blebbing, Poroelasticity, Hydrostatic pressure

Soft Matter

Cells are great examples of heterogeneous structured fluids. Their autonomous nature makes them particularly interesting to study for synthetic mimickry. With current interests in using polymer systems for tissue engineering and drug delivery, cells are an obvious system to look to for inspiration. Cell blebbing for instance occurs during apoptosis when the cytoplasm is breaking up and the cell is dismantling itself. A programmed separation of a heterogeneous polymeric system would be very desireable for use in implantable tissue engineering models for a variety of reasons. Understanding an optimized system such as the cell is an important step in advancing polymer engineering, and engineering of soft matter.

Here the author sets out to change current methodology for thinking about a model of the cell cytoplasm. Very simply, the mechanism of blebbing is explained with respect to the hydrostatic pressure within the cell system.

Blebbing essentially is a result of non-equilibrium of the cell membrane. There is currently a discrepancy as to whether the inequilibrium is a result of globally uniform hydrostatic pressure with local nucleation of membrance dettachment from the cytoskeleton, or from globally non-equilibrium hydrostatic pressure leading to dettachment in areas of high pressure.

First, a detailed description of blebbing dynamics is established through confirmations made using fluourescence microscopy.

By using drugs affecting membrance rigity, osmotic pressure, myosin, and actin function, local disruptions of cortical contraction were studied in cells that bleb profusely.