The significance of the relative effects of loop diuretics and anti-brain edema agents on the Na+,K+,Cl- cotransport system and the Cl-/NaCO3- anion exchanger.

3-Amino-5-sulfamoylbenzoic acids and several series of (aryloxy)alkanoic acids were evaluated for their inhibitory effects on two human erythrocyte ion transport systems--the Na+,K+ cotransport system and the DIDS-sensitive anion carrier. Several classic loop diuretics, including the (aryloxy)alkanoic acid-ethacrynic acid and several 3-amino-5-sulfamoylbenzoic acids, like bumetanide and furosemide, displayed relatively strong inhibitory activity versus the cotransport system with relatively weaker action versus the anion carrier. Furthermore, diuretic potency correlated with cotransport inhibitory potency. Another class of (aryloxy)alkanoic acids, namely the [(2,3-dihydro-1H-inden-5-yl)oxy]acetic acids, such as indacrinone and MK-473, which exhibit less potent loop diuretic activity, were less potent cotransport inhibitors and more effective inhibitors of the anion carrier. Still other (aryloxy)alkanoic acids, with little saliuretic activity, namely a sub-class of [(2,3-dihydro-1H-inden-5-yl)oxy]alkanoic acids and a series of [(2,3,9,9a-tetrahydro-1H-fluoren-7-yl)oxy]acetic acids displayed little or no inhibitory action on the cotransport system but enhanced inhibitory action on the anion carrier. Most interestingly, the relative anion carrier inhibitory potency correlated well with the relative inhibitory activity of each compound on bicarbonate-stimulated cell swelling in cat cerebrocortical slices.