Osmotic stress and DNA damage.

Mammalian renal inner medullary cells are normally exposed to extremely high NaCl concentrations. The interstitial NaCl concentration in parts of a normal renal medulla can be 500 mM or more, depending on the species. Remarkably, under these normal conditions, the high NaCl causes DNA damage, yet the cells survive and function both in cell culture and in vivo. Both in cell culture and in vivo the breaks are repaired rapidly if the NaCl concentration is lowered. This chapter describes two methods used to detect and study the DNA damage induced by osmotic stress: comet assay or single cell electrophoresis and TUNEL assay or in situ labeling of 3'-OH ends of DNA strands. This chapter also discusses how specifics of the protocols influence the conclusions about types of DNA damage and what the limitations of these methods are for detecting different types of DNA damage.