Mechanisms of gastrointestinal copper absorption in the African walking catfish: Copper dose-effects and a novel anion-dependent pathway in the intestine

In mammals, copper (Cu) absorption occurs mostly in the small intestine, an d some of the Cu transporters involved in its uptake have been characterise d, In fish, however, the regions of the gut involved in Cu absorption and t he membrane transport mechanisms responsible for gastrointestinal Cu uptake are unknown, Everted gut sacs and isolated perfused intestine of Clarias g ariepinus were used to explore Cu absorption (at 22 degrees C), Gut sacs ex posed to 100 mu mol l(-1) mucosal solution Cu ([Cu](m)) showed that Cu was mostly (70 %) absorbed in the middle and hind intestine. Most of the accumu lated Cu was located in the mucosa, In perfused intestines, cumulative Cu a bsorption from the mucosal solution to the serosal perfusate was greatest a t 10 mu mol l(-1) [Cu](m) and decreased at higher values of [Cu](m), while tissue accumulation of Cu showed a dose-dependent elevation. Absorption eff iciency therefore declined with increasing Cu dose, and basolateral transpo rt was the limiting factor in Cu uptake, Serosal applications of the P-type ATPase inhibitor vanadate (100 mu mol l(-1)) or the anion transport inhibi tor DIDS (100 mu mol l(-1)) caused threefold increases in net Cu uptake (at [Cu](m)=10 mu mol l(-1)). The vanadate effect was explained by a reduction in transepithelial potential rather than inhibition of Cu-ATPase, but the DIDS effect was not. Transepithelial potential, water transport and tissue [Cu] were not affected by DIDS, but tissue [K+] was elevated. Removal of Cl - simultaneously from both the mucosal and serosal solutions caused a 10-fo ld reduction in the rate of Cu uptake, while removal of Cl- from the mucosa l solution only completely abolished Cu absorption to the serosal perfusate , Transepithelial potential effects are discussed. We conclude that Cu abso rption occurs mostly in the intestine and is normally driven by a basolater al Cu/anion symport that prefers Cl-.