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)

Abstract

This report describes a unique response of the anion transporter in equine erythrocytes to the fluorescent substrate N-(2-aminoethyl sulfonate)-7-nitrobenz-2-oxa-3-diazole (NBD-taurine). Equine erythrocytes showed fluxes of NBD-taurine both inward and outward at rates considerably slower than those in human cells. These fluxes were completely abolished by a typical anion transport inhibitor, 4, 4'-diisothiocyanostilbene-2, 2'-disulfonate. Furthermore, NBD-taurine competitively inhibited the uptake of phosphate in equine red cells with an inhibition constant of phosphate that was slightly higher than the Michaelis constant of phosphate uptake. These results demonstrate that the anion transporter (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 portion which is implicated in anion transport.