ION-TRANSPORT IN THE FRESH-WATER BIVALVE CORBICULA-FLUMINEA

In freshwater bivalves such as the mussel Corbicula fluminea, uptake o f chloride depends on the external concentration of the chloride ion. In C. fluminea, Cl- uptake displayed saturation kinetics both in anima ls acclimated to pondwater and in those subjected to salt depletion by storage in deionized water. The transport capacity (J(max)) was 7.00 +/- 0.51 mu eq g(-1) dry tissue h(-1) and the transport affinity (K-m) was 0.21 +/- 0.08 mM in animals acclimated to pondwater. Animals subj ected to salt depletion had a higher rate of Cl- uptake than did anima ls acclimated to pondwater. After 4 weeks in deionized water, the long er the animals were salt-depleted, the higher their rate of Cl- uptake . Na+ and Cl- transport were independent in pondwater-acclimated C. fl uminea. For salt-depleted animals, Cl- transport was Na+-independent, but Na+ transport depended partially on external Cl-. Serotonin stimul ated Cl- and Na+ transport in pondwater-acclimated animals by increasi ng influx while having little influence on efflux. Acetazolamide incre ased the Cl- and Na+ efflux of salt-depleted animals. Both serotonin a nd acetazolamide elevated the net loss of titratable base.