Sulfate transport across the peritubular surface of the marine teleost renal tubule.

The uptake of sulfate across the peritubular surface of isolated renal tubules of seawater-acclimated winter flounder, Pseudopleuronectes americanus, consisted of two phases. The fast exchanging component appeared to be a small sulfate compartment with a saturable uptake rate; however, the Km was quite large (14.5 mM). The fast phase was partially inhibited by the anion transport inhibitor 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene (SITS), but was unaffected by antimycin A, which indicated lack of ATP-dependence. The slowly exchanging compartment was fourfold larger than the fast, saturable with a low Km (0.65 mM), and inhibited by antimycin A, SITS, ouabain, and Na-free incubation medium. Phosphate appeared to be a noncompetitive inhibitor of this phase. These observations support the idea that the slow phase of sulfate uptake may be driven by the peritubular membrane Na gradient. This mediated, energy-dependent uptake may be part of the active sulfate secretory pump of the marine teleost renal tubule.