Effect of calcium oxalate on renal cells as revealed by real-time measurement of extracellular oxidative burst

Calcium oxalate is one of the main constituents of kidney stones and has a proved deleterious effect on renal cells that is mediated by oxidative stress. However, the subcellular source of this oxidative stress, and whether it is extending to the extracellular space or not, is still disputed. Therefore, an electrochemical superoxide biosensor was constructed, positioned above A6 renal cells, and used to measure in real-time the extracellular oxidative burst following addition of calcium oxalate crystals. It was observed that A6 cells do secrete superoxide into their extracellular space in few minutes after encountering calcium oxalate crystals. The amount of released superoxide peaks at about 20 min. Superoxide is cleared away from the extracellular space after approximately 3 h. Superoxide secretion depends on the presence of superoxide-scavenging enzyme superoxide dismutase, the age of the cells, the amount of calcium oxalate crystals, and the temperature. Moreover, the effect of calcium oxalate crystals was mimicked by phorbol 12-myristate 13-acetate. The developed sensing system can be a useful tool for biologists investigating nephrolithiasis at cellular level.