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.
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