Fig. 4. Effect of luminal zinc (20 µmol l^–1) and L-leucine 100 µmol l^–1) on the kinetics of transmural transport of ³H-L-histidine (1–50 µmol l^–1) measured over 30 min time intervals at each luminal ³H-L-histidine concentration. Unidirectional fluxes were calculated from regression slopes determined over this time interval for each ³H-L-histidine concentration. Values displayed are means ± S.E.M. of 3 replicates per concentration.