Fig. 9. Effect of luminal pH on the time course of 20 µmol l^{–1 3}H-L-histidine (L-His) transport by perfused lobster intestine in the presence of 20 µmol l^–1 zinc (control, pH 7.1; test, pH 6.1). Values displayed are means ± S.E.M. of 3 replicates per time point. Slopes of the lines were calculated as regression lines using Sigma Plot software and the values on the figure (i.e. m-values) are the slopes obtained from these analyses at each condition used.