VOLUME-ACTIVATED TAURINE EFFLUX FROM SKATE ERYTHROCYTES - POSSIBLE BAND-3 INVOLVEMENT

In a previous study (L. Goldstein, S. R. Brill, and E. V. Freund, J. Exp. Zool. 254: 114-118, 1990) it was suggested that volume-activated (VA) taurine efflux from skate (Raja erinacea) erythrocytes might involve the anion exchanger band 3. The aim of the present study was to obtain further evidence for (or against) this possibility. We found that in addition to stilbene disulfonates, two other band 3 inhibitors, N-(azido-2-nitrophenyl)-2-amino sulfonic acid (NAP)-taurine and niflumic acid, also inhibit VA taurine efflux. In addition, there is a close relationship between the dose-response curves for 4,4'-diisothiocyanostibene-2,2'-disulfonic acid inhibition of VA taurine efflux and sulfate efflux. Furthermore, taurine influx, as well as efflux, is activated by volume expansion, as would be expected with transport facilitated by band 3. However, sulfate (a known band 3 substrate) efflux is not activated by volume expansion, and sulfate influx is only activated minimally, but sulfate does inhibit VA taurine uptake. Thus there is considerable evidence in favor of the involvement of band 3 in VA taurine efflux, but the issue of the sulfate fluxes remains to be resolved.