Shear stress induces a time- and position-dependent increase in endothelial cell membrane fluidity

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 () 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- of 10 or 20 dyn/cm², and after the cessation of . 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- 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 .D returned to near control values within 5 s aftercessation of . 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- 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- 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.