LOOP DIURETICS AFFECT TRANSCELLULAR ELECTROLYTE TRANSPORT IN CELLS OFTHE DISTAL CONVOLUTED TUBULE

Although loop diuretics act preferentially on sodium chloride absorpti on in the thick ascending limb of the loop of Henle in the nephron, hi gh concentrations of some loop diuretics also impair sodium absorption in the distal convoluted tubule (DCT). To characterize further the in hibitory effect of these agents on sodium absorption in the DCT, the a ction of torsemide and furosemide on cell sodium, chloride and potassi um concentrations was examined in individual DCT cells of the kidney c ortex and also, for comparison, in proximal convoluted tubule cells. I n addition, initial cell uptake rates of rubidium, an index of in vivo Na+/K+-ATPase activity, were studied. Both diuretics caused a signifi cant reduction of intracellular sodium concentration and rubidium upta ke in DCT cells but not in connecting tubule, principal, intercalated or proximal tubule cells. These findings are consistent with the conce pt that both diuretics reduce transcellular sodium absorption in DCT c ells by impairing sodium entry across the apical cell membrane and, as a consequence, sodium extrusion by primary active Na+/K+(Rb+) exchang e across the basolateral membrane.