Application of physiological shear stress to renal tubular epithelial cells.

Renal tubular epithelial cells are consistently exposed to flow of glomerular filtrate that creates fluid shear stress at the apical cell surface. This biophysical stimulus regulates several critical renal epithelial cell functions, including transport, protein uptake, and barrier function. Defining the in vivo mechanical conditions in the kidney tubule is important for accurately recapitulating these conditions in vitro. Here we provide a summary of the fluid flow conditions in the kidney and how this translates into different levels of fluid shear stress down the length of the nephron. A detailed method is provided for measuring fluid flow in the proximal tubule by intravital microscopy. Devices to mimic in vivo fluid shear stress for in vitro studies are discussed, and we present two methods for culture and analysis of renal tubule epithelial cells exposed physiological levels of fluid shear stress. The first is a microfluidic device that permits application of controlled shear stress to cells cultured on porous membranes. The second is culture of renal tubule cells on an orbital shaker. Each method has advantages and disadvantages that should be considered in the context of the specific experimental objectives.