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

Abstract

Toxolasma texasensis acclimated to an artificial pondwater (PW) maintained a concentration of SO4 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 35SO4 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 ml g(-1) dry tissue h(-1), and provided an estimate of renal filtration in PW-acclimated animals. The clearance of radioactive 35SO4 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 SO4 reabsorbed was significantly reduced relative to mussels acclimated to PW. T. texasensis conserved SO4 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.

Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca

“…Furthermore, clearance of 35 SO 4 injected into T. texasiense individuals was 16% of a simultaneously injected chemical, polyethylene glycol, used to measure renal filtration rates, indicating that SO 4 2− was reabsorbed by the kidney [25]. Similar results were obtained for pond water-acclimated D. polymorpha (Supplemental Data, Table S9).…”

“…Similar results were obtained for pond water-acclimated D. polymorpha (Supplemental Data, Table S9). Although the transporter for SO 4 2− is still unclear, the inhibition of the ion’s uptake by DIDS, an anion exchanger inhibitor, suggests an anion exchanger (Figure 5 and Table 2) [25,320]. …”

“…In most fish and amphibians, the ion concentrations or osmolality of intracellular (i.e., the cytosol or fluids within cells) and extracellular (i.e., the fluids outside of cells, particularly the blood or hemolymph) fluids remain relatively constant as the water osmolality increases. Most invertebrates, including unionid mussels [25] and freshwater Crustacea, are hyperregulators in freshwater and become isosmotic when placed in brackish or salt waters [3,31,32]. Hemolymph ion concentrations in freshwater molluscs are lower than in either fish or arthropods [24].…”

Roles of Slc13a1 and Slc26a1 sulfate transporters of eel kidney in sulfate homeostasis and osmoregulation in freshwater

“…Physiological studies on sulfate homeostasis also have been conducted in nonmammalian systems, including those of birds (12,40,44,45), bivalve (11), and fish (10, 36, 37, 43, 46 -49). However, little is known concerning their molecular mechanisms.…”

Functional and structural characterization of the zebrafish Na+-sulfate cotransporter 1 (NaS1) cDNA and gene (slc13a1)

“…Recently, using a gene targeted approach, we generated a NaS1 null mouse (6), which has reduced serum sulfate levels (hyposulfatemia), confirming NaS1 is essential for maintaining sulfate homeostasis in mice. Functional sulfate transport studies have been performed in nonmammalian eukaryotes, including birds (9, 30), mussels (8), and fish (7,27,29,31), but little is known about the molecular structures of these transporters. Several fish sulfate transporters have been recently characterized.…”