The dependence on chloride ions of the loop diuretic sensitive component of passive sodium efflux from human red cells.

A study has been made of the passive (ouabain-insensitive) Na efflux from human red cells. The inhibition by loop diuretics (furosemide, piretanide and bumetanide) was additive with respect to ouabain and non-additive with respect to each other. They inhibited with high affinity in the sequence bumetanide greater than piretanide greater than furosemide. Passive Na efflux was not inhibited by amiloride, DIDS or SITS. In Cl-free media, Na efflux was reduced and there was no diuretic-sensitive component with any of the six Cl substitutes tested, except Br. The chloride concentration dependence of the diuretic-sensitive efflux was generally linear but saturable with sulphate and concave with acetate. In Na-free media, efflux was reduced, the apparent affinity for loop diuretics was lower and there was no chloride dependence. The diuretic-insensitive efflux was unaffected by anions in all conditions.