EFFECTS OF DIURETICS ON CALCIUM EXCRETION AND Ca²⁺-ACTIVATED ATPase IN RAT KIDNEY

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Effects of three diuretics on the urinary Ca²⁺ excretion and on the microsomal Ca²⁺-activated ATPase were examined in the rat kidney. Furosemide and bumetanide increased Na⁺, K⁺, and Ca²⁺ excretion in the rats. Acetazolamide increased Na⁺ and K⁺ excretion but not Ca²⁺. Urinary inorganic phosphate excretion was not affected during the administration of acetazolamide. It is suggested that acetazolamide inhibits Na⁺ transport without affecting Ca²⁺ reabsorption in the rat nephron. Microsomal ATPase of the rat kidney cortex was stimulated by Ca²⁺ or Mg²⁺ alone and an additive effect of the two cations was not observed. Microsomal ATPase activated by Ca²⁺ or Mg²⁺ was not inhibited by furosemide, bumetanide, and acetazolamide. These data suggest that the inhibitory effect of furosemide and bumetanide on the Ca²⁺ reabsorption is not related to the inhibition of Ca²⁺-activated ATPase.