title: High-affinity binding is essential for enhancement of intestinal Fe2+ and Ca2+ uptake by bile salts.
abstract: Both calcium and iron are bound with high affinity by premicellar bile salts having cholanic ring 7-OH and/or 12-OH groups, forming soluble cation-bile salt complexes. The authors of the current study recently showed that premicellar taurocholate markedly enhances intestinal iron and calcium uptake. However, the relationship of high-affinity binding to the observed uptake enhancement was unknown. In the current study, this relationship was examined by studying taurodehydrocholate (TDHC) binding and intestinal uptake of both cations. Ca2+ binding was measured by noting depression of [Ca2+] activity in solutions containing constant total Ca concentrations (1 mmol/L) and varying [TDHC] (0.5-50 mmol/L). Fe2+ binding was assessed by equilibrium dialysis studies of 59FeSO4 (0.179-1.79 mmol/L) and TDHC (0.5-50 mmol/L). Effects of TDHC on intestinal Fe2+ and Ca2+ uptake were measured in isolated perfused intestinal segments in vivo in seven and eight Sprague-Dawley rats, respectively. TDHC, lacking ring OH groups, did not bind either cation with high affinity and had no effect on their intestinal uptake. These results suggest that high-affinity binding is essential for bile salt-induced enhancement of intestinal Fe2+ and Ca2+ uptake.
authors.affiliation: Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond.
authors.forename: A J
authors.initials: AJ
authors.lastname: Sanyal
authors.forename: J I
authors.initials: JI
authors.lastname: Hirsch
authors.forename: E W
authors.initials: EW
authors.lastname: Moore
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects*; D007501:Iron / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013656:Taurocholic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology
chemical_list: D001647:Bile Acids and Salts; C019560:taurodehydrocholate; D013656:Taurocholic Acid; D007501:Iron; D002118:Calcium