Fluid Shear Stress Effects on Endothelial Cell Cytosolic pH

Abstract

Fluid flow can modulate endothelial cell intracellular pH (pH_i). Venous and arterial shear stresses of 1.4 and 14 dyn/cm2, respectively, induced intracellular acidification. The kinetics of the process and magnitude of acidification were dependent on the level of shear stress. Endothelial cells exposed to a venous shear stress were able to recover from the acidification, whereas cells exposed to an arterial shear stress remained acidic. Addition of SITS (1 mM), a HCO₃ ^–/CI^– exchange inhibitor, greatly reduced the shear stress induced acidification, suggesting that the HCO₃ ^–/C1^– exchanger is activated by shear stress. Shear stress may activate the exchanger by lowering the [HCO₃ ^–] at the cell surface via convective mass transfer. Altering the HCO₃ ^– gradient across the cell membrane activates the exchanger and, as a consequence, results in intracellular acidification. Perfusion with media containing ATP (10 µM) altered the kinetics of flow-induced acidification observed at both shear stress levels. ATP modulation of pH_i may be coupled to the rise in [Ca²⁺]_j known to occur with ATP stimulation. To summarize, media perfusion induces intracellular acidification in endothelial cells, and there is evidence to suggest that pH_i may serve as a second messenger to modulate flow associated changes in endothelial cell metabolism.