BASOLATERAL TAURINE TRANSPORT-SYSTEM IN REPTILIAN RENAL-CELLS

The characteristics of taurine transport across renal basolateral memb ranes were examined, using basolateral membrane vesicles (BLMV) isolat ed from garter snake (Thamnophis spp.) kidneys. BLMV fraction exhibite d high enrichment for the basolateral marker enzyme, Na+-K+-adenosinet riphosphatase (23-fold), with similar to 10% contamination by brush-bo rder membranes. Taurine uptake into BLMV was specifically stimulated b y inwardly directed Na+ gradient in the presence of Cl-. Equilibrium N aCl condition and replacement of NaCl gradient by KCl, choline chlorid e, NaSCN, sodium gluconate, or mannitol inhibited taurine uptake. Unli ke brush-border membrane vesicles (BBMV), taurine uptak:e into BLMV wa s not stimulated by a Cl- gradient. In further contrast to BBMV, BLMV taurine uptake was smaller in magnitude and not electrogenic. The stoi chiometric relationship between Na+ and BLMV taurine uptake, determine d by activation method, indicated a 1 Na+:1 taurine interaction, in co ntrast to the 3 Na+:1 taurine stoichiometry for BBMV taurine transport . Bromcresol green inhibited BBMV taurine transport but had no effect on BLMV taurine uptake. Efflux of taurine from BLMV was faster than th at from BBMV. Unlike BBMV, the BLMV efflux was stimulated by external taurine. The observed characteristics of taurine transport on both mem branes would integratively result in net transepithelial reabsorption of taurine across renal cells of the garter snake, a species that demo nstrates both net reabsorption and secretion of taurine in vivo.