Fig. 1. Effects of (A) forskolin (10 µmol l^–1), (B) theophylline (3 mmol l^–1) and (C) dibutyryl cyclic AMP (db-cAMP; 500 µmol l^–1) on unidirectional and net L-alanine fluxes across the duodenum of Gallotia galloti. 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. Drugs were added in small volumes (<50 µl) to both sides of the tissue immediately after the last control values were obtained and were left for an additional 10 min before test samples were taken (see Materials and methods). Results are means ± S.E.M. for 16, 12 and 8 different duodenal segments, respectively. J_ms, mucosa-to-serosa flux; J_sm, serosa-to-mucosa flux; J_net, net flux. *P<0.05; **P<0.01 compared with control.