VOLUME-ACTIVATED AMINO-ACID-TRANSPORT AND CELL SIGNALING IN SKATE ERYTHROCYTES

Skate (and other fish) erythrocytes show a rapid efflux of taurine in response to volume expansion upon exposure to hyptonic medium. Taurine and other small amino acids appear to be released from the cells down their concentration gradients via a channel which might involve the anion exchange protein Band 3. Hypotonicity alters the cell permeability to taurine coincident with generation of diacylglycerol from phosphatidylcholine by stimulating the activity of phospholipase D. This diacylglycerol can then activate protein kinase C, stimulating the phosphorylation of specific protein targets. Three phosphoprotein targets have been identified; one is the Band 3 molecule itself, while the other two have molecular weights of 67 and 34 kDa. The precise way in which phosphorylation alters the permeability of the cell to taurine is as yet unknown. It is possible that phosphorylation of Band 3 changes the molecule so that it acts as an amino acid channel. (C) 1994 Wiley-Liss, Inc.