Shear-induced volume decrease in MDCK cells

Using a microfluidic cell volume sensor we measured the change in the cell volume of Madin-Darby Canine Kidney (MDCK) cells induced by shear stress. An increase in shear stress from 0.2 to 2.0 dyn/cm ² resulted in a volume decrease to a steady state volume ∼ 20-30 % smaller than the initial resting cell volume. Independent experiments based on fluorescence quenching confirmed the volume reduction. This shear-induced cell shrinkage was irreversible on the time scale of the experiment (∼ 30 min). Treatment of 0.1 μM Hg ²⁺ significantly inhibited the volume decrease, suggesting that the shear-induced cell shrinkage is associated with water efflux through aquaporins. The volume decrease cannot be inhibited by 75 mM TEA, 100 μM DIDS, or 100 μM Gd ³⁺ suggesting that volume reduction is not directly mediated by K ⁺ and Cl ^- channels that typically function during regulatory volume decrease (RVD), nor is it through cationic stretch-activated ion channels (SACs). The process also appears to be Ca ²⁺ independent because it was insensitive to intracellular Ca ²⁺ level. Since cell volume is determined by the intracellular water content, we postulate that the shear induced reductions in cell volume may arise from increased intracellular hydrostatic pressure as the cell is deformed under flow, which promotes the efflux of water. The increase in internal pressure in a deformable object under the flow is supported by the finite element mechanical model.