THE INTRACELLULAR MECHANISM OF SALINITY TOLERANCE IN POLYCHAETES: VOLUME REGULATION BY ISOLATEDGLYCERA DIBRANCHIATARED COELOMOCYTES

Abstract

Glycera dibranchiata is an osmoconforming polychaete that lives in seawater osmotic concentrations ranging from 1366 to 374 mosm/kg. G. dibranchiata uses free amino acids (FAA) to reduce intracellular solute concentrations during hypoosmotic stress: Both body wall tissue and isolated red coelomocytes taken from worms adapted to dilute seawater for 14 days showed substantial decreases in several amino acids when compared to full-strength seawater controls. Measurements of cell volume made on isolated red coelomocyte suspensions during acute exposure to dilute media indicate that volume regulation is rapid but incomplete. The volume of red coelomocytes does not return to control values during 120 min. The volume recovery of the isolated coelomocytes during hypoosmotic stress is accompanied by salinity-dependent efflux of FAA proline and taurine. A comparison of this efflux with the FAA pool in full-strength-seawater acclimated cells indicates that the effiux is accomplished by a selective change in membrane permeability to proline and taurine.