Taurine secretion in cultured winter flounder renal epithelium

The mechanism for the secretion of taurine by the marine fish kidney was examined in flounder renal primary cultures and teased tubules. The question addressed was whether the secretion of taurine, but not beta-alanine, a related beta-amino acid, is due to differences in their basolateral uptake, intracellular concentration, or luminal efflux mechanism. Aminooxyacetate (AOA) (10 mM), an inhibitor of beta-alanine oxidation, allowed the basolateral beta-alanine accumulation (measured in teased tubules) and the beta-alanine intracellular concentration (measured in primary cultures) to be similar to that for taurine. However the addition of AOA did not promote the net secretion of beta-alanine (measured as unidirectional fluxes in the cultured epithelium mounted in an Ussing chamber). The organic anions bromcresol green (BCG) (0.1 mM) and probenecid (1 mM) inhibited the net secretion of taurine by affecting the luminal efflux step. This suggests that a BCG- and probenecid-sensitive carrier in the luminal membrane facilitates the cell-to-lumen efflux of taurine and thus achieves net secretion.