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Shear stress induces a time- and position-dependent increase in endothelial cell membrane fluidity
Authors:Butler P J  Norwich G  Weinbaum S  Chien S
Affiliation:The Whitaker Institute of Biomedical Engineering and Department of Bioengineering, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0427, USA.
Abstract:Blood flow-associatedshear stress may modulate cellular processes through its action on theplasma membrane. We quantified the spatial and temporal aspects of theeffects of shear stress (tau ) on the lipid fluidity of1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate [DiIC16(13)]-stained plasma membranesof bovine aortic endothelial cells in a flow chamber. A confocalmicroscope was used to determine the DiI diffusion coefficient(D) by fluorescence recovery after photobleaching on cellsunder static conditions, after a step-tau of 10 or 20 dyn/cm2, and after the cessation of tau . The methodallowed the measurements of D on the upstream and downstreamsides of the cell taken midway between the respective cell borders andthe nucleus. In <10 s after a step-tau of 10 dyn/cm2,D showed an upstream increase and a downstream decrease, and both changes disappeared rapidly. There was a secondary, larger increase in upstream D, which reached a peak at 7 min and decreased thereafter, despite the maintenance of tau .D returned to near control values within 5 s aftercessation of tau . Downstream D showed little secondarychanges throughout the 10-min shearing, as well as after its cessation.Further investigations into the early phase, with simultaneousmeasurements of upstream and downstream D, confirmed that astep-tau of 10 dyn/cm2 elicited a rapid (5-s) but transientincrease in upstream D and a concurrent decrease indownstream D, yielding a significant difference between thetwo sites. A step-tau of 20 dyn/cm2 caused D toincrease at both sites at 5 s, but by 30 s and 1 min theupstream D became significantly higher than the downstream D. These results demonstrate shear-induced changes inmembrane fluidity that are time dependent and spatially heterogeneous. These changes in membrane fluidity may have important implications inshear-induced membrane protein modulation.

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