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 micromol/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 Ca(2+)-free solution, and was inhibited by alkaline pH. The inhibitor of anion exchange protein, 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (IC(50)=25 microM) and the Cl(-) channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid and [(dihydro-indenyl) oxy] alkanoic acid (IC(50)<20 microM) 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.
Katz
U
U
Department of Biology, Technion, Israel Institute of Technology, Haifa, Israel. bir02@tx.technion.ac.il
Lancaster
J A
JA
Ellory
J C
JC
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000468:Alkalies / Q000494:pharmacology; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000037:antagonists & inhibitors; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002264:Carboxylic Acids / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007038:Hypotonic Solutions / Q000494:pharmacology*; D007192:Indenes / Q000494:pharmacology; D007477:Ions; D009579:Nitrobenzoates / Q000494:pharmacology; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000097:blood; D013654:Taurine / Q000037:antagonists & inhibitors / Q000097:blood*; D014982:Xenopus laevis / Q000097:blood*
D000468:Alkalies; D001457:Anion Exchange Protein 1, Erythrocyte; D002264:Carboxylic Acids; D018118:Chloride Channels; D002712:Chlorides; D007038:Hypotonic Solutions; D007192:Indenes; D007477:Ions; D009579:Nitrobenzoates; D013654:Taurine; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D011189:Potassium Chloride; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium