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

Pondwater-acclimated Dreissena polymorpha maintained a sulfate concentratio n of about 2-3 mmol/L in the hemolymph. Sulfate was accumulated from the me dium by a mechanism that was inhibited by diisothiocyanatostilbene disulfon ic acid. The clearance of polyethylene glycol (PEG) injected into the hemol ymph 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 t he kidney. Abolishing the osmotic gradient by acclimating D. polymorpha to 10% seawater reduced PEG clearance to 0.3 mL/(g dry tissue.h). Sulfate clea rance in animals acclimated to 10% seawater was similar to PEG clearance. T hus, D. polymorpha conserved sulfate when acclimated to the low-sulfate pon d water, but not when acclimated to the more sulfate-rich 10% seawater medi um.