Fig. 2. Effect of luminal ³H-L-histidine concentration (1–50 nmol l^–1 µmol l^–1) on the rate of mucosal-to-serosal transmural transport measured in the absence of mucosal zinc over 30 min time intervals at each luminal amino acid concentration. Unidirectional fluxes were calculated from regression slopes determined over this time interval for each amino acid concentration. Values displayed are means ± S.E.M. of 3 replicates per concentration.