Uptake of selenate and selenite by isolated intestinal brush border membrane vesicles from pig, sheep, and rat

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Abstract
Selenate and selenite uptakes by isolated intestinal brush border membrane vesicles (BBMV) from pig, sheep, and rat were investigated. Selenate uptake into jejunal and ileal, but not duodenal, BBMV from pig was stimulated by an inwardly directed transmembrane Na+ gradient (Na out + >Na in + ). Selenate transport into rat ileal and sheep jejunal BBMV was also enhanced in the presence of a Na+ gradient. Unlike selenate uptake, selenite uptake was not Na+ dependent, neither in pig small intestine nor in sheep jejunum and rat ileum. Uptake of selenate represented real uptake into the vesicular lumen, whereas selenite uptake was a result of an extensive binding of75Se to the membranes. Thiosulfate at a 250-fold concentration of selenate completely inhibited Na+-dependent selenate uptake into pig jejunal BBMV. Furthermore, Na+-dependent sulfate uptake was totally inhibited in the presence of a 250-fold selenate concentration. The results clearly show that selenate transport across the BBM of pig jejunum and ileum, sheep jejunum, and rat ileum is partially energized by a transmembrane Na+ gradient. Moreover, it is concluded from the results that there exists a common transport mechanism for sulfate and selenate in the BBM. The extensive binding of75Se from75Se-labeled selenite to the membranes could be from a spontaneous reaction of selenite with membrane-associated SH groups.