VOLUME-ACTIVATED OSMOLYTE CHANNEL IN SKATE ERYTHROCYTES - INHIBITION BY PYRIDOXAL DERIVATIVES

Volume expansion of erythrocytes of Little skate, Raja erinacea, trigg ers the opening of an osmolyte channel. We review this transport mecha nism and further investigate the channel's physicochemical nature by p robing the channel with a series of pyridoxine derivatives in skate RB C as well as in epithelial cells: MDCK and C6 glioma cells and in skat e hepatocytes. The identity of the transport mechanism (band 3 vs. an anion channel) which mediates the swelling-activated efflux of osmolyt es in fish RBC is controversial. Therefore, we compared taurine and Cl - effluxes in similar conditions. We found that there is significant C l- loss from volume-expanded skate RBC. However, there was no effect o f either hypotonicity or a number of taurine transport inhibitors on t his loss. Utilizing changes in intracellular pH as a means of indirect ly measuring H+/Cl- cotransport, we found that a rise in cell pH accom panied the loss of Cl-. This suggests that Cl- efflux could occur via a H+/Cl- cotransporter. To probe and compare the osmolyte channel (tau rine efflux) of the skate RBC and three other cell types we used a fam ily of pyridoxine inhibitors. The inhibitory patterns for the skate er ythrocytes and hepatocytes differed from those for MDCK and C6 glioma cells and the two former cell. types differed from each other. Therefo re, the results show that the osmolyte channel in the skate differs fr om that in other epithelial cells with regard to pyridoxine derivative binding properties. (C) 1997 Wiley-Liss, Inc.