Fig. 3. Effects of (A) calcium ionophore A23187 and (B) extracellular calcium replacement on duodenal unidirectional and net L-alanine fluxes. Experiments were carried out under short-circuit conditions in the presence of sodium. The concentration of L-alanine was 1 mmol l^–1 throughout the experiments and was added to both serosal and mucosal bathing solutions 20 min before the control values were obtained. A23187 (0.5 µmol l^–1) was added to both sides of the tissue immediately after the last control values were obtained. Calcium replacement was achieved by replacing all the standard solution with a Ca²⁺-free solution containing 0.5 mmol l^–1 EGTA. Tissues were left for an additional 10 min before test samples were taken (see Materials and methods). Results are means ± S.E.M. for 16 and 10 duodenal segments, respectively. J_ms, mucosa-to-serosa flux; J_sm, serosa-to-mucosa flux; J_net, net flux. **Statistically different from its corresponding control value at P<0.01.