Cytotoxic effects of calcium on sodium-potassium transport in the mammalian lens

Abstract

The effects of lens Ca on the Na/K pump were investigated [in humans] since elevated Ca and Na often accompanies lens opacification. An increase in lens Ca was accomplished by culturing lenses in Ca-rich media at 21.degree. C in the absence of poisons which might directly alter Na transport. Ca loaded lenses were subsequently incubated at 37.degree. C in a normal culture medium to assess membrane transport function. A 5-fold increase in total lens Ca to 1.45 mM, resulting in a 4% increase in membrane bound Ca, had little effect on the cation pump. An increase in lens Ca by a factor of 100 caused a 4-fold increase in membrane bound Ca, a 50% decrease in (Na/K)-ATPase activity and a 40% decrease in 86Rb uptake after an incubation period of 20 h. Details of the mechanism of enzyme inhibition remain obscure, but the data suggest the inhibition is predominantly irreversible and does not involve an interaction between Ca and ATP.