The influence of luminal pH on transport of neutral and charged dipeptides by rat small intestine, in vitro

摘要

Four hydrolysis-resistant dipeptides (-phenylalanyl--alanine, -phenylalanyl--glutamine, -phenylalanyl--glutamate and -phenylalanyl--lysine) were synthesized to investigate the effects of net charge on transmural dipeptide transport by isolated jejunal loops of rat small intestine. At a luminal pH of 7.4 and a concentration of 1 mM the two dipeptides with a net charge of ?1 and +1 were transported at substantially slower rates (18±1.3 and 8.4±1.3 nmol min?1 (g dry wt.)?1, respectively) than neutral -phenylalanyl--alanine and -phenylalanyl--glutamine (87±0.2 and 197±14 nmol min?1 (g dry wt.)?1, respectively). We investigated the effects of luminal pH on dipeptide transport by varying the NaHCO3 content of Krebs Ringer perfusate equilibrated with 95%O2/5% CO2. The pH changes did not affect water transport, but serosal glucose appearance increased significantly at pH 6.8. Transmural transport of -phenylalanyl--alanine and -phenylalanyl--glutamine at pH 6.8 was stimulated (P<0.01) by 61% and 49%, respectively, whereas the lower pH increased the rate for negatively charged -phenylalanyl--glutamate by 306% (P<0.01) and decreased that for positively charged -phenylalanyl--lysine by 46% (P<0.05). Increasing luminal pH to 8.0 inhibited -phenylalanyl--alanine transport by 60%, whereas -phenylalanyl--lysine transport was 60% faster.