Effects of diuretics on calcium uptake and release in renal microsomes

A variety of diuretics were tested for their effects on Ca²⁺ uptake and release by microsomes isolated from rat kidneys. Mersalyl acid, ethacrynic acid, furosemide and bumetanide inhibited Ca²⁺ uptake by microsomes. Cysteine abolished the inhibitory effects of mersalyl acid and ethacrynic acid on Ca²⁺ uptake. No appreciable differences in the inhibition were seen between microsomes from kidney cortex and those from medulla. Acetazolamide had no significant effect on Ca²⁺ uptake; however. hydrochlorothiazide stimulated Ca²⁺ uptake activity. The effects of the diuretics on Ca²⁺ uptake by microsomes were entirely on the process of Ca²⁺ accumulation in microsomes, since release of Ca²⁺ that had been taken up previously was not influenced by any of the diuretics tested. These results provide information concerning the biochemical mechanisms of action of diuretics on Ca²⁺ reabsorption in the kidney.