Osmolyte channel regulation by ionic strength in skate RBC

The aim of this study was to determine whether the opening of the osmolyte channel in skate red blood cells (RBC) is regulated by intracellular electr olyte concentration and conductivity. Consistent with previous studies, exp eriments with hyperosmotic preincubation before cell swelling or swelling w ith an isosmotic electrolyte (e.g., ammonium chloride) showed that an incre ase in ionic strength inhibits the opening of the taurine channel. However, a decrease in intracellular ionic strength did not always stimulate taurin e efflux to the same degree. Whereas hyposmotic swelling caused a large inc rease in taurine efflux, swelling induced by treatment with isosmotic nonel ectrolytes produced much smaller stimulation. Results with assays for band 3 phosphorylating enzymes were consistent with those from the taurine efflu x studies; stimulation of enzyme activity was lower in cells that were swol len with isosmotic nonelectrolyte media than in cells swollen in hyposmotic media. These results indicate that a decrease in ionic strength is not the only signal for the opening of the taurine channel in skate RBC. Ionic str ength does affect channel activity, but there must also be some other regul ator.