Transport of selenate and sulphate across the intestinal brush-border membrane of pig jejunum by two common mechanism.

The objectives of the present study were to find out whether selenate and sulphate are transported by a common Na+-dependent transport mechanism across the intestinal brush-border membrane and whether selenate is also transported by the anion-exchange system transporting sulphate across the brush-border membrane. Results from cis-inhibition as well as from trans-stimulation experiments show that selenate and sulphate are transported across the brush-border membrane by both Na+ co-transport and anion exchange. The influence of various dicarboxylates (oxalate, oxaloacetate, glutamate) and of the anion-exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS) on selenate and sulphate transport across the brush-border membrane was also investigated. Under Na+-gradient conditions selenate uptake across the brush-border membrane was reduced by oxalate and oxaloacetate but not by L-glutamate or L-leucine. Additionally sulphate uptake under this condition was significantly inhibited by oxalate (about 50%) and DIDS (25%). Sulphate transport by anion exchange was inhibited about 80% by both oxalate and DIDS. These results suggest that under Na+-gradient conditions sulphate (selenate) uptake in part occurs via anion exchange. Furthermore, oxalate seems to inhibit both Na+-sulphate (selenate) co-transport and sulphate (selenate) transport by anion exchange.