Since blood flow exerts both shear stress and cyclic strain on a vessel walls, it has been hypothesized that these forces modulate the function of endothelial cells (EC) lining the inner wall. The interaction may involve direct mechanical events at the cell membrane interface, alterations of mass transport processes or by a streaming potential effect created by the movement of charged blood across the electronegatively charged endothelium. It is only recently that experimental models which apply physical forces to cells in culture have been utilized. Much of our previous knowledge of EC biology has come from studies of cultured cells maintained in a stationary environment in vitro, which may be inappropriate for the study of their behavior in vivo. Our laboratory has characterized a device which can apply different regimens of cyclic tensional deformation on attached monolayers of cultured EC. This repetitive force in vitro may be analogous to the pulsatile strain experienced by cells of the vessel wall in vivo. Using this apparatus, we have demonstrated that chronic cyclic strain can modulate vascular cell phenotype in culture, manifested by alterations in growth, morphology and secretion of a number of products. The molecular basis and intracellular signals governing these changes in cell function are complex and not well elucidated. We postulate that it is the periodic fluctuations in the different components of the forces of the circulation that initiate a cascade of events that is sensed by the EC membrane and ultimately produces a cell response. The overall objective of this proposal, therefore, is to determine the mechanism by which EC in culture respond to cyclic strain regimens. We plan to test the following hypotheses: 1) Varying the frequency or amplitude of a cyclic strain force on EC in culture will induce an immediate (seconds) increase in cytosolic calcium but will not affect potassium channels. 2) Varying the frequency or amplitude of a cyclic strain force on EC in culture will result in a prompt (seconds) activation of the phosphinositol (PI) pathway. 3) Varying the frequency or amplitude of a cyclic strain force on EC in culture will cause early (minutes) stimulation of the adenylate cyclase system. The clinical relevance of this proposal is the potential to contribute insights into the transducing signals by which hemodynamic forces, in particular cyclic strain, stimulate EC proliferation and secretion of macromolecules in vitro. Such information might provide a rationale approach to modulating the in vivo responses of EC by altering the generation of these second messengers.
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