Taurine reabsorption by a carrier interacting with furosemide in short and long Henle's loops of rat nephrons.

Taurine is net reabsorbed in the proximal convolution by Cl- -stimulated Na+ symport specific for beta-amino acids but not in later nephron segments. However, large unidirectional taurine transport takes place there. To investigate unidirectional taurine reabsorption, we comicroinfused [3H]taurine and [14C]inulin into late proximal (LP), early distal (ED), and late distal (LD) tubule segments, as well as into the tips of long loops of Henle (LLH) of rats in vivo, and determined fractional reabsorption of [3H]taurine (FR) in the ipsilateral urine. FR (9 micromol/l taurine) was 80-93 (LP), 16 (ED), and 8% (LD). At 26 mmol/l taurine, FR decreased to 13 (LP) and 6% (ED). FR also decreased when Na+ or Cl- was absent or furosemide (5 x 10(-5) mol/l) was added. Bumetanide (5 x 10(-5) mol/l) had no effect, whereas aniline-2-sulfonic acid (ASA) inhibited. During LLH microinfusion, FR was 55% at 66 micromol/l and 17% at 228 micromol/l and was again inhibited by furosemide and ASA but not by bumetanide. [14C]taurine reabsorption from microperfused proximal convolutions was not influenced by furosemide. Chronic water diuresis did not affect taurine reabsorption in short Henle's loops. We conclude that taurine can enter cells of the distal nephron from the lumen by an Na+- and partly Cl- -dependent carrier with which C alpha,beta-substituted taurine (ASA) and C alpha,beta- and N-substituted beta-alanine (furosemide) directly interact. Thus proximal and distal taurine carriers seem to be different.