The biology of strontium: interactions with the mammalian crystalline lens

Rabbit lenses incubated in a Ca-free medium gain Na and lose K, but this effect is reduced by the presence of strontium. Little Sr enters the lens under in vitro conditions and that which is present does not appear to significantly enter the lenticular cells. The Sr present, however, appears to be displaced by lanthanum, suggesting that Sr is interacting with the cell surface. This outer 'bound' Sr does not interfere with exchanges of Ca across the cell membrane but it may contribute to the control of lens permeability to Na and K. Uptake of Sr can be enhanced by exposure of the lens to a Ca-free medium or the Ca-Mg ionophore A23187.