The influence of luminal pH on transport of neutral and charged dipeptides by rat small intestine, in vitro.
Four hydrolysis-resistant dipeptides (D-phenylalanyl-L-alanine, D-phenylalanyl-L-glutamine, D-phenylalanyl-L-glutamate and D-phenylalanyl-L-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 D-phenylalanyl-L-alanine and D-phenylalanyl-L-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% 02/5% CO2. The pH changes did not affect water transport, but serosal glucose appearance increased significantly at pH 6.8. Transmural transport of D-phenylalanyl-L-alanine and D-phenylalanyl-L-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 D-phenylalanyl-L-glutamate by 306% (P < 0.01) and decreased that for positively charged D-phenylalanyl-L-lysine by 46% (P < 0.05). Increasing luminal pH to 8.0 inhibited D-phenylalanyl-L-alanine transport by 60%, whereas D-phenylalanyl-L-lysine transport was 60% faster.
Lister
N
N
Department of Biology, University of York, UK.
Bailey
P D
PD
Collier
I D
ID
Boyd
C A
CA
Bronk
J R
JR
D000818:Animals; D001692:Biological Transport; D004151:Dipeptides / Q000138:chemical synthesis / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007583:Jejunum / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014882:Water-Electrolyte Balance
D004151:Dipeptides; D005947:Glucose