Transport characteristics of p-acetamidobenzoic acid in brush border membrane of rat small intestine.

Brush border membrane vesicles of rat small intestinal mucosa were prepared by the modified calcium precipitation method in order to investigate the intestinal secretion mechanism of p-acetamidobenzoic acid (Ac-PABA). The release rate of [14C]-Ac-PABA from preloaded vesicles was much faster than that of p-aminobenzoic acid (PABA) and was enhanced by the addition of unlabelled Ac-PABA in the outer medium. In contrast, the membrane transfer rate of Ac-PABA across the egg lecithin liposomes was slower than that of PABA. The contribution of a carrier-mediated transport mechanism in the brush border membrane to the intestinal secretion of Ac-PABA was suggested.