LIGHT, D.B.; HELM, E.M.; MASON, L.Z.; SHELLY, J.L.; Lake Forest College; Lake Forest College; Lake Forest College; Lake Forest College: Regulated Volume Decrease in Salmo salar Erythrocytes

Salmo salar (Atlantic salmon) is an anadromous euryhaline teleost whose gills are exposed to a wide range of salinities during its life cycle. With this in mind, we examined regulated volume decrease (RVD) in erythrocytes of this species. Cell volume was measured electronically with a Coulter counter (model Z2). Exposure of erythrocytes to a hypotonic (0.5X) Ringer caused cells to quickly swell, which was followed by a slower, spontaneous RVD. Replacing extracellular NaCl with KCl or exposing cells to a high taurine (90 mM) Ringer inhibited volume recovery. In addition, quinine (10 mM) partially inhibited RVD, whereas the phospholipase A2 antagonist ONO-RS-822 (10 &microM) completely blocked volume recovery. In contrast, the ATP scavenger hexokinase (2.5 U/ml) or addition of ATP (100 &microM) to the extracullar medium had no affect. We also monitored intracellular Ca²⁺ levels with fluo-4-AM (10 &microM) and epi-fluorescence microscopy. In an isotonic solution, cells displayed little or no fluorescence. In contrast, fluorescence increased following hypotonic shock; and this effect was partially inhibited with the stretch-activated channel blocker gadolinium (10 &microM) or by bathing cells in a low Ca²⁺ (10 nM, buffered with EGTA) Ringer. Finally, and interestingly, this cell type displayed an RVD-like response in isotonic Ringer. This affect was apparent even when Na⁺ was replaced with choline; its cause remains to be elucidated. Conclusions: Regulated volume decrease in S. salar erythrocytes depends on efflux of taurine and KCl. Solute efflux during volume recovery is associated with a rise in intracellular calcium and depends on arachidonic acid or its metabolites. (Supported by funds from Lake Forest College).