Premicellar taurocholate enhances calcium uptake from all regions of rat small intestine

Abstract

Background/Aims: The specific components of bile, which is necessary for normal calcium absorption, are unknown. We have previously shown that Ca2+ is bound with high affinity by premicellar taurocholate. The current studies examined the effects of taurocholate on intestinal calcium transport. Methods: Intestinal Ca2+ uptakes were measured from proximal, mid, and distal small intestinal segments perfused with solutions containing 45 CaCl2 (0.1–1 mmol/L), taurocholate (0–10 mmol/L), trihydroxymethylaminomethane buffer (pH 7), phenolsulfonpthalein (nonabsorbable marker), and NaCl (total ionic strength, 0.16 mol/L) for four randomized perfusion periods. In other studies, the proximal small intestine was divided into two equal segments and perfused with either 45CaCl2 or 45CaCl2 plus taurocholate (2.5–5 mmol/L). Calcium absorption was measured from the difference in uptake and calcium concentration retained in mucosa. Finally, effects of taurocholate on Ca2+ uptake across isolated brush border membrane vesicles were measured. Results: Premicellar taurocholate produced an approximately 1.7–2-fold enhancement (P < 0.01) in Ca2+ uptake in all regions, with lesser contributions from micellar taurocholate. These effects resulted in a net increase in calcium absorption. Premicellar taurocholate also significantly increased calcium uptake across brush border vesicles. Conclusions: Premicellar taurocholate significantly enhances calcium uptake into, and absorption across, enterocytes. The mechanisms remain to be experimentally verified.