A NOVEL RESPONSE OF ANION TRANSPORTER IN EQUINE ERYTHROCYTES TO A FLUORESCENT SUBSTRATE, N-(2-AMINOETHYL SULFONATE)-7-NITROBENZ-2-OXA-3-DIAZOLE (NBD-TAURINE)

This report describes a unique response of the anion transporter in eq uine erythrocytes to the fluorescent substrate N-(2-aminoethyl sulfona te)-7-nitrobenz-2-oxa-3-diazole (NBD-taurine). Equine erythrocytes sho wed fluxes of NBD-taurine both inward and outward at rates considerabl y slower than those in human cells. These fluxes were completely aboli shed by a typical anion transport inhibitor, 4, 4'-diisothiocyanostilb ene-2, 2'-disulfonate. Furthermore, NBD-taurine competitively inhibite d the uptake of phosphate in equine red cells with an inhibition const ant of phosphate that was slightly higher than the Michaelis constant of phosphate uptake. These results demonstrate that the anion transpor ter (band 3) in equine red cells binds NBD-taurine but does not prefer it as the substrate for transport, suggesting a structural difference between equine and human anion transporters at the polypeptide portio n which is implicated in anion transport.