FIGURE 5: Regulation of endocytosis by mechanical stress. Proximal tubule cells are tasked with the uptake of proteins and other molecules from the glomerular filtrate. Increased fluid shear stress bends primary cilia, thereby triggering Ca²⁺ influx that is further amplified intracellularly. Via activation of Calmodulin this change induces Cdc42-mediated actin polymerization and enhanced endocytosis to prevent proteinuria (see section ”Mechanical stress” for further details).