Effect of Diuretics on Ion Transport of Kidney Cortex Mitochondria: III. Species Difference in Calcium Accumulation and in Ethacrynic Acid Effect

Abstract

Effect of inorganic phosphate (4×l0−3 M) on Ca++-accnmulation was examined in kidney cortex mitochondria. Ca++w-accumulation of rat kidney cortex mitochondria was slightly influenced by inorganic phosphate. On the other hand, dog kidney cortex mitochondria did not accumulate calcium from the incubation medium until the inorganic phosphate had been added. Ca++-accumulation of rabbit kidney cortex mitochondria was markedly stimulated by inorganic phosphate. When ethacrynic acid was added to the reaction medium in the absence of inorganic phosphate, Ca++-accumuiation of rat kidney cortex mitochondria was depressed and the decrease in calcium content of rabbit and dog kidney cortex mitochondria was enhanced. In the presence of inorganic phosphate, the inhibition of Ca++-accumula-tion by ethacrynic acid was observed only on dog kidney cortex mitochondria. Subsequently, the effect of inorganic phosphate (4×10−4 M) and ethacrynic acid (1×10−4 M) on Ca++-ATPase was examined in kidney cortex mitochondria. The low concentration of inorganic phosphate (4×10−4 M) activated Ca++-ATPase of kidney cortex mitochondria in all animal species. The greatest activation of Ca++-ATPasc occurred in rabbits, but the activity of the enzyme was lower than that in rats and dogs. Inhibition of Ca++-ATPase by ethacrynic acid was depressed by the addition of inorganic phosphate in kidney cortex mitochondria of experimental animals. Camaccumulation may be regulated through the stimulating effect of inorganic phosphate and the inhibitory effect of ethacrynic acid on Ca++-ATPase in kidney cortex mitochondria. Species difference in ethacrynic acid effect on Ca++-accumulation in kidney cortex mitochondria of rats, rabbits and dogs is discussed.