Adhesion force between calcium oxalate monohydrate crystal and kidney epithelial cells and possible relevance for kidney stone formation

AFM interaction force measurements have been performed between calcium oxalate monohydrate crystal (COM) colloidal probes and monolayers of renal epithelial cells (on a polymer substrate) in artificial urine (AU) solutions. The adhesion force was measured for the COM/MDCK cell interaction, while no adhesion force was found for the COM/LLC-PK1 cell interaction. Long-range repulsive forces for both lines of cells were measured in the range of 2–3 μm. After removal of the cell from the substrate by the AU flow, the basal membrane (BM), with a thickness of 100–200 nm, remained on the substrate. In this case, the shorter-range repulsive forces were found on the extending (approaching) portion of force/indentation curves. Similar to the COM/MDCK cell interaction, the retracting portions of curves for COM/basal membranes have shown the existence of the attractive force of adhesion for the interaction of COM with a BM of MDCK cells, while no adhesion was found for COM/BM LLC-PK1 cells interaction. No adhesion force was found for the interaction of a BM (of any cells) with the silicon nitride tip. Besides the hydrodynamic reasons, the adhesion difference between LLC-PK1 and MDCK cells possibly explains the preferential deposition of crystals only in collecting ducts (lined with MDCK-type cells) and the lack of the crystal deposition in the proximal tubules (lined with LLC-PK1-type cells). Previous treatments of cells with oxalate alone increased the adhesion force COM/BM MDCK; however, even after oxalate treatment there was small or no adhesion between COM and BM LLC-PK1 cells. Note that the adhesion force for COM/BM MDCK is practically independent of the probe velocity, i.e., does not have the viscous origin. Evaluation of the adhesion energy shows that this force should be related to the ionic or hydrogen bonds of samples.

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