Hypotonic-induced transport pathways in Xenopus laevis erythrocytes:: taurine fluxes

Taurine fluxes in Xenopus laevis red cells were studied in vitro in media of different tonicities. Both influx and efflux increased 3-10 times reversibly when dilution of the medium exceeded 30%. The absolute values of uptake ranged between 5 and 30 mumol/l cells(.)h at extracellular taurine concentration of 1 mmol/l, but is poorly selective as almost the same uptake was measured for choline and sucrose. Q(10) of 2.77 and an activation energy of 71.90 +/- 7.37 kJ/mol were calculated for the uptake process. Taurine uptake was. reduced 50% in the absence of Cl-, whereas the alkali cations (Na+, K+, Li+ and Rb+) supported it similarly. Taurine uptake was greatly increased in Ca2+-free solution, and was inhibited by alkaline pH. The inhibitor of anion exchange protein, 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (IC50 = 25 muM) and the Cl- channel blockers, 5-nitro-2-(3-phenylpropylamino) benzoic acid and [(dihydro-indenyl) oxy] alkanoic acid (IC50 < 20 muM) inhibited taurine uptake effectively. Isoproterenol did not affect taurine uptake in isotonic, nor in hypotonic solution. The uptake was reduced slowly to near the original, control level within 15-30 min in hypotonic solutions, indicating deactivation of the hypotonic-induced taurine pathway. (C) 2002 Elsevier Science Inc. All rights reserved.