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Abstract
The research presented in this dissertation examined the response of endothelial cells in culture to a quantified mechanical stimulus in order to study the endothelial cell's mechanotransduction system. To this end, a system was presented which exposed endothelial cells in culture to measurable biaxial extensional strains applied through cell attachments to a biaxially elongated substrate. Cell strains were measured as significantly less than those of the substrate and demonstrated dependence on cell morphology and variability among cell populations. This range in cell strain was examined by a viscoelastic lumped parameter approach. Results indicated that the cell's measured biomechanical response depended upon the mechanical properties of the elements of the cytoarchitecture and cell-matrix adhesion mechanics. Utilizing the system, cell strain was shown to be an important stimulus for biochemical responses of the endothelial cell. Measured strain-induced alterations in cytosolic calcium ion homeostasis, in the form of calcium-dependent fluorescence transients using Quin2 and Fura2, were proposed as a possible signal for these physiologic changes. The source of these transients was shown to be release from intracellular stores through alterations in cell calcium permeability. The strain-induced cytosolic calcium concentration transients were hypothesized to involve two phases: strain-enhanced calcium transport which resulted in release of calcium from intracellular stores into the cytosol and a recovery phase, which tended to drive the cytosolic calcium concentration back to a baseline level. Analysis of the recovery phase was addressed and was based on species conservation and chemical kinetics. Results suggested that the level and time course of cytosolic accumulation of calcium depended upon a balance of hypothesized mechanically-altered cell calcium permeability and the kinetics of active and passive calcium sequestering mechanisms. Experimental and analytical data presented here suggest that alterations in cytosolic calcium ion concentration could be achieved by altering mechanically the balance of the cell's calcium permeability and sequestering mechanisms. This mechanically-induced net calcium accumulation might be an important stimulus in promoting strain-induced biochemical changes in cells.
