D-glucose triggers multidrug resistance-associated protein (MRP)-mediated secretion of fluorescein across rat jejunum in vitro

To examine the transport characteristics of the multidrug resistance-associated protein (MRP) substrate fluorescein across the isolated rat small intestinal segments. The transport of fluorescein was studied in side-by-side diffusion chambers under short-circuited conditions at physiological pH. The serosal-to-mucosal permeability of fluorescein significantly exceeded the permeability in the opposite direction in the jejunum, but not in the ileum. This asymmetry in transport in the jejunum was observed only when D-glucose was present at the mucosal side of the tissue, and not in the presence of D-galactose or D-mannitol. In the presence of D-glucose at the mucosal side, serosal-to-mucosal permeability of fluorescein in the jejunum can be divided into an active (Michaelis-Menten constant, KM = 1.07 mM; maximum flux of the substrate. Jmax = 14.0 nmol/h x cm2) and a passive component (passive permeability, Ppas = 2.51 x 10(-6) cm/s). The polarization of fluorescein transport was almost completely abolished by MRP inhibitor, benzbromarone (50 or 100 microM, applied apically), and by MRP/P-glycoprotein inhibitor, verapamil (200 microM, applied apically). D-glucose at the mucosal side activates fluorescein secretion across rat jejunum by an apical MRP, most probably by isoform 2 (MRP2), which could have an impact on the intestinal absorption of MRP substrates.