Science Buddies: "Ask an Expert"

Cells can adapt to high salt but how is this achieved? Upon exposure to salt, cells must immediately restore lost volume. They do this by importing salt, which draws water back into the cell. However, excess salt inside a cell hinders its function. This dilemma is resolved by energy-consuming mechanisms that slowly pump excess salt out of the cell. These are replaced by more compatible, uncharged substances called ‘osmolytes’. Our research group recently explored in detail intracellular changes induced by salt by live-cell microscopy using a variety of fluorescent dyes that label cellular components, such as the cytoskeleton, organelles, as well as chloride ions themselves. When we exposed cells to non-lethal doses of salt, the movement of the organelles and cytoskeleton froze and then slowly recovered. Surprisingly, the recovery of movement was not fast like cell volume recovery, but instead followed the slow removal of excess chloride. When we added a chemical that allowed chloride to enter the cells passively, a dramatic reduction in movement was also observed. When higher doses of salt were used, cells could not remove all of the extra chloride, and movement remained persistently slower. We compared many cell types, including liver, pancreatic, and white blood cells, and found that recovery was fastest in kidney cells, which are very efficient at removing excess chloride. Together, these data imply that while loss of volume and compression certainly contribute to cellular damage, lingering excess chloride also contributes to the long-term toxicity of high salt.