The loop diuretic furosemide as a non-competitive inhibitor of Cl −/HCO 3−-ATPases of vertebrate kidneys and insect rectum

Abstract

1. The effect of the diuretic drug furosemide was studied in detail on ouabain-insensitive, SCN − and OCN −-sensitive Cl −/HCO 3 −-ATPase in homogenates from larval dragonfly rectum ( Aeshna cyanea), frog ( Rana temporaria) and mouse ( Mus musculus) kidney. 2. The in vitro inhibition by the drug studied on the HCO 3 −-activated enzyme is non-competitive with an inhibitor constant of K i = 4.3 mM furosemide in the case of insect rectum and K i = 0.9 mM furosemide in the case of frog and mouse kidney. 3. Furosemide even at 10 mM concentration which completely inhibits the anion-dependent ATPase has only a little inhibitory effect on the Na +/K +-ATPase of the 3 tissues. 4. The data suggest that furosemide may affect an active chloride transport system involving a Cl −/HCO 3 −-ATPase.