Effect of aluminum on bidirectional calcium flux in rat everted intestinal sacs

The effect of aluminum on intestinal calcium absorption was determined in male Sprague-Dawley rats using an everted intestinal sac technique. Bidirectional calcium flux in the duodena and ilea of normal rats was assessed by means of dual calcium isotopes. Two micromolar aluminum significantly inhibited net calcium absorption (J net) in the duodenum through suppression of mucosato-serosa flux (J m----s). Jm----s was reduced from 2.21 +/- 0.50 mumol Ca.h-1.g wet wt-1 in controls to 0.93 +/- 0.35 mumol Ca.h-1.g-1 in aluminum exposed sacs, and Jnet was reduced from 1.88 +/- 0.14 mumol Ca.h-1.g-1 to 0.55 +/- 0.41 mumol Ca.h-1.g-1 (P less than 0.001). Serosa-to-mucosa calcium flux (Js----m) was not similarly influenced by aluminum. Inhibition of Jm----s occurred whether aluminum was initially present on the mucosal or serosal side of the duodenal sac and inhibition of Jnet calcium by 2 muM A1 occurred at all ambient concentrations of calcium studied. In the ileum, aluminum had no effect on any component of calcium flux. Aluminum did not induce any suppression of glucose transport in either the duodenum or ileum, suggesting that the effect on calcium transport is relatively specific. These results suggest that aluminum inhibits calcium absorption in the duodenum through an effect on active mucosa-to-serosa transport, but has no effect on ileal calcium absorption, which in the rat is not mediated by an active process.