ENDOCYTOSIS IN UROTHELIAL UMBRELLA CELLS: ENDOCYTIC VESICLES TRAFFIC pp. 67-91
Authors: Ernesto J. Grasso, Reyna O. Calderon, Cell Biology Institute, School of Medicine, National University of Cordoba, Argentina
Abstract: Endocytosis is defined as a process where patches of membrane are invaginated and budded off of specialized domains of the plasma membrane. The receptor-mediated endocytosis or clathrin dependant is the most studied mechanism, followed by caveolar and non-clathrin dependant. But in diverse type of cells, such as umbrella cells from the uroepithelium, changes in plasma membrane tension are capable to induce endocytosis. This process occurs by hydrostatic pressure changes during micturion cycle, is clathrin independant and an intact cytoskeleton is necessary. When hydrostatic pressure increases, during urinary bladder filling-phase of micturition cycle, the umbrella cells are stretched and a fusion process of subapical vesicles to apical plasma membrane occurs. After plasma membrane relaxation, during the voiding-phase of the cycle, the additional membrane is endocytosed as discoidal vesicles entrapping the luminal fluid phase. This peculiar endocytosis/exocytosis process, different from the classical endocytosis mechanism, result an appropriate membrane model to study the membrane traffic but also the urinary fluid traffic. The late may have physiophatological implications since the toxins present in the urinary fluid may effectively be delivered to the cell machinery instead to be recycled to the bladder lumen.