FREE AMINO-COMPOUNDS AND CELL-VOLUME REGULATION IN ERYTHROCYTES FROM DIFFERENT MARINE FISH SPECIES UNDER HYPOOSMOTIC CONDITIONS - THE ROLE OF A TAURINE CHANNEL

Erythrocytes from the marine fish species ballan wrasse (Labrus berggy lta Ascanius), bullhead (Myoxocephalus scorpius L.), cod (Gadus morhua L.), dab (Limanda limanda L.), eelpout (Zoarces viviparus L.), flound er (Platichthys flesus L.), lumpfish (Cyclopterus lumpus L.), plaice ( Pleuronectes platessa L.), sole (Solea solea L.) and turbot (Scophthal mus maxima L.) possess the capacity for regulatory volume decrease. Th is property was demonstrated in vitro by reduction of the osmolality o f the incubation medium from 330 to 255 mosmol.kg(-1). During the 4-h incubation period only the lumpfish cells completely regained the orig inal volume. Twenty-seven free amino compounds were present in detecta ble amounts in the erythrocytes. At normal osmolality the taurine cont ent was between 14.0 mu mol.g dry weight(-1) (lumpfish) and 147.4 mu m ol.g dry weight(-1) (sole). Except in the bullhead, taurine was the qu antitatively dominating amino compound in the erythrocytes from all sp ecies, and accounted for between 23% (lumpfish) and 88% (sole) of the total content of free amino compounds. In each species the regulatory volume decrease was associated with a reduction in the cellular conten t of taurine. Taurine contributed to between 6% (lumpfish) and 36% (fl ounder) of the cell shrinkage. There was a significant negative correl ation, however, between the cellular concentration of taurine at norma l osmolality and the capacity of the cells for regulatory volume decre ase. Gamma-aminobutyric acid and/or glycine also contributed to the pr ocess of volume regulation, but to a lesser extent than taurine. The v olume regulatory efflux of taurine and gamma-aminobutyric acid were me diated by taurine channels. It is suggested that these channels also m ediated the reduction in the cellular contents of glycine.