Ion Transport in the Freshwater Bivalve Corbicula fluminea

In freshwater bivalves such as the mussel Corbicula fluminea, uptake of chloride depends on the external concentration of the chloride ion. In C. fluminea, Cl- uptake displayed saturation kinetics both in animals acclimated to pondwater and in those subjected to salt depletion by storage in deionized water. The transport capacity (Jmax) was 7.00 +/- 0.51 {mu}eq g-1 dry tissue h-1 and the transport affinity (Km) was 0.21 +/- 0.08 mM in animals acclimated to pondwater. Animals subjected to salt depletion had a higher rate of Cl- uptake than did animals acclimated to pondwater. After 4 weeks in deionized water, the longer the animals were salt-depleted, the higher their rate of Cl- uptake. Na+ and Cl- transport were independent in pondwater-acclimated C. fluminea. For salt-depleted animals, Cl- transport was Na+-independent, but Na+ transport depended partially on external Cl-. Serotonin stimulated Cl- and Na+ transport in pond-water-acclimated animals by increasing influx while having little influence on efflux. Acetazolamide increased the Cl- and Na+ efflux of salt-depleted animals. Both serotonin and acetazolamide elevated the net loss of titratable base.