Measurement of sulfate uptake and loss in the freshwater bivalve Dreissena polymorpha using a semi-microassay

Pondwater-acclimated Dreissena polymorpha maintained a sulfate concentration of about 2-3 mmol/L in the hemolymph. Sulfate was accumulated from the medium by a mechanism that was inhibited by diisothiocyanatostilbene disulfonic acid. The clearance of polyethylene glycol (PEG) injected into the hemolymph of D. polymorpha was 2-3 mL/(g dry tissue.h) and provided an estimate of the renal filtration rate in pondwater-acclimated animals. The clearance of sulfate injected into pondwater-acclimated D. polymorpha was about 20% of the PEG clearance, suggesting that the sulfate was being reabsorbed by the kidney. Abolishing the osmotic gradient by acclimating D. polymorpha to 10% seawater reduced PEG clearance to 0.3 mL/(g dry tissue.h). Sulfate clearance in animals acclimated to 10% seawater was similar to PEG clearance. Thus, D. polymorpha conserved sulfate when acclimated to the low-sulfate pond water, but not when acclimated to the more sulfate-rich 10% seawater medium.