Loop diuretics affect transcellular electrolyte transport in cells of the distal convoluted tubule

Although loop diuretics act preferentially on sodium chloride absorption in the thick ascending limb of the loop of Henle in the nephron, high concentrations of some loop diuretics also impair sodium absorption in the distal convoluted tubule (DCT). To characterize further the inhibitory effect of these agents on sodium absorption in the DCT, the action of torsemide and furosemide on cell sodium, chloride and potassium concentrations was examined in individual DCT cells of the kidney cortex and also, for comparison, in proximal convoluted tubule cells. In addition, initial cell uptake rates of rubidium, an index of in vivo Na+/K(+)-ATPase activity, were studied. Both diuretics caused a significant reduction of intracellular sodium concentration and rubidium uptake in DCT cells but not in connecting tubule, principal, intercalated or proximal tubule cells. These findings are consistent with the concept that both diuretics reduce transcellular sodium absorption in DCT cells by impairing sodium entry across the apical cell membrane and, as a consequence, sodium extrusion by primary active Na+/K+ (Rb+) exchange across the basolateral membrane.