Flow stimulated apical endocytosis in renal proximal tubule epithelia (892.6)

Abstract

The kidney is able to maintain solute and fluid reabsorption over a wide range of GFRs. Internalization of filtered low molecular weight proteins, vitamins, hormones, and other small molecules is mediated by the proximal tubule (PT) multiligand receptors megalin and cubilin. Microvillar bending in response to increases in GFR and the accompanying fluid shear stress (FSS) modulates PT ion transport capacity. However, whether FSS affects endocytosis in PT cells is unknown. Exposure of rat kidney slices to FSS led to a dramatically increased internalization of the megalin/cubilin ligand albumin and the fluid phase marker dextran in cortical tubules. Similar results were observed when PT cell lines were subjected to physiologically relevant levels of FSS. Flow stimulated endocytosis was initiated by 15‐30 min post induction of FSS, was clathrin‐ and dynamin‐dependent, and was rapidly reversed. FSS also caused a rapid elevation in intracellular Ca2+ levels, which was not observed in deciliated cells or upon inclusion of apyrase in the medium. Strikingly, deciliation and apyrase treatment also blocked the flow dependent increase in endocytosis. We hypothesize that changes in intracellular Ca2+ in response to flow‐dependent ciliary bending triggers the observed increase in PT apical endocytosis via a mechanism that involves extracellular ATP‐dependent calcium release from intracellular stores.Grant Funding Source: Supported in part by the Lowe Syndrome Association