Oxalate-induced exposure of phosphatidylserine on the surface of renal epithelial cells in culture

A molecular mechanism of crystal attachment to renal cells after injury has been proposed in which the exposure of phosphatidylserine (PS) on the cell membrane surface following injury provides attachment sites for calcium-co ntaining crystals. Annexin V was used to determine whether injury to kidney cells by oxalate in culture resulted in PS exposure on the cell surface. W hen continuous cultures of intermedullary collecting duct cells were expose d to various levels of oxalate, a dose-dependent increase in PS exposure wa s observed on the cell surfaces. Initially, only scattered cells expressed PS on the surface. However, as the level of oxalate increased, groups of ce lls began to express PS, suggesting that the injured cells may have an infl uence on neighboring cells. Exposure of PS on the cell membrane surface cor related with a corresponding increase in calcium oxalate monohydrate crysta l attachment to the cells. This indicates that damage to kidney epithelial cells by elevated concentrations of urinary components, in this case oxalat e, could result in exposure of PS on cells, which could provide a point of fixation or nucleation for calcium-containing crystals.