Anion-selectivity of the swelling-activated osmolyte channel in eel erythrocytes

Osmotic swelling of fish erythrocytes activates a broad-specificity permeation pathway that mediates the volume-regulatory efflux of taurine and other intracellular osmolytes. This pathway is blocked by inhibitors of the erythrocyte band 3 anion exchanger, raising the possibility that band 3 is involved in the volume-regulatory response. In this study of eel erythrocytes, a quantitative comparison of the pharmacology of swelling-activated taurine transport with that of band 3-mediated SO4(2-) transport showed there to be significant differences between them. N-ethylmaleimide and quinine were effective inhibitors of swelling-activated taurine transport but caused little, if any, inhibition of band 3. Conversely, DIDS was a more potent inhibitor of band 3-mediated SO4(2-) flux than of swelling-activated taurine transport. In cells in isotonic medium, pretreated then co-incubated with 0.1 mM DIDS, the band 3-mediated transport of SO4(2-) and Cl- was reduced to a low level. Exposure of these cells to a hypotonic medium containing 0.1 mM DIDS was followed by the activation of a Cl- permeation pathway showing the same inhibitor sensitivity as swelling-activated taurine transport. The data are consistent with swelling-activated transport of taurine and Cl- being via a common pathway. A comparison of the swelling-activated transport rates for taurine and Cl- with those for several other solutes was consistent with the hypothesis that this pathway is an anion-selective channel, similar to those that mediate the volume-regulatory efflux of Cl- and organic osmolytes from mammalian cells.