Chloride and taurine effluxes occur by different pathways in skate erythrocytes

The aim of this study was to determine whether volume-activated taurine and Cl- effluxes occur via the same system in skate (Raja erinacea) red blood cells (RBC). The effluxes were measured in isotonic and hypotonic elasmobranch Ringer solutions, in which NaCl was replaced by mannitol and the remaining exchangeable anions with gluconate. Methazolamide (0.1 mM) was added to minimize HCO3- formation. RBC Cl- content fell approximately 50%/h in both isotonic and hypotonic media, with no detectable K- loss in either medium. The observed Cl- loss was accompanied by an increase in pH. Both the Cl- loss and pH rise were inhibited by 4,4'- diisothiocyanostilbene-2,2'-disulfonic acid (0.1 mM), suggesting that Cl- efflux was due to H(+)-Cl- cotransport. 36Cl- effluxes in isotonic and hypotonic media were (means +/- SE, n = 11) 2.8 +/- 0.6 and 3.5 +/- 0.9 mumol.g dry wt RBC-1.min-1, respectively, whereas [3H]taurine effluxes in the same media were 0.045 +/- 0.02 and 2.1 +/- 0.05 mumol.g dry wt RBC-1.min-1, respectively (n = 6). These results indicate that taurine and Cl- effluxes occur via different pathways in skate RBC. In addition, the swelling-activated Cl- channel reported in epithelial cells does not appear to be present in skate RBC. This conclusion was confirmed by Western blots with an antibody to swelling-activated Cl- channels. Taurine and Cl- fluxes are apparently under different pathway influences in these RBC: taurine diffuses via a channel, whereas Cl- is transported by cotransporters.