Kidney function and sulfate uptake and loss in the freshwater bivalve Toxolasma texasensis

Toxolasma texasensis acclimated to an artificial pondwater (PW) maintained a concentration of SO, in the blood of about 1-2 mmol l(-1). The anion transport inhibitor DIDS (5, 5'-diisothiocyanatostilbene 2, 2'-disulfonic acid) reduced the uptake of (SO4)-S-35 from the bathing medium by 54%. The clearance of polyethylene glycol (PEG) injected into the blood of T. texasensis ranged between 0.8 and 1.3 mi g(-1) dry tissue h(-1), and provided an estimate of renal filtration in animals. The clearance of radioactive (SO4)-S-35 simultaneously injected into the same animal was about 16% of the PEG clearance, suggesting that sulfate was being reabsorbed by the kidney. Para-aminohippuric acid was cleared about 4.6 times faster than PEG, indicating that this organic acid was subjected to secretion in addition to filtration. When the normal osmotic gradient was abolished by acclimating T. texasensis to 10% seawater (SW) the PEG clearance decreased to 0.17 ml g(-1) dry tissue h(-1). Sulfate clearance in animals acclimated to PW or 10% SW was the same. However, in mussels acclimated to 10% SW, the calculated amount of SO, reabsorbed was significantly reduced relative to mussels acclimated to PW. T. texasensis conserved SO, when acclimated to PW, and reduced reabsorption when acclimated to the sulfate-rich 10% SW. When mussels acclimated to 10% SW were returned to PW, there was a transient increase in sulfate clearance during the first 8 h because filtration exceeded reabsorption.