Effect of zinc on D-galactose and L-phenylalanine uptake in rat intestine in vitro.
The effect of zinc on galactose and phenylalanine uptake was studied using rat everted jejunal rings. The rings were incubated for 2 min in oxygenated Krebs-Ringer-Tris (KRT) solution. Galactose and phenylalanine uptake was reduced by zinc in a dose-dependent manner, but not in a time-dependent way. One mM Zn2+ but not 0.5 mM Zn2+ inhibited galactose transport without modifying sugar diffusion. Na(+)-dependent phenylalanine transport was reduced by 0.5 mM and 1 mM Zn2+. However, the metal did not change phenylalanine diffusion obtained in the presence of 40 mM L-methionine or Na(2+)-independent phenylalanine transport. Therefore, zinc seems to interact only with the sodium-galactose or sodium-phenylalanine cotransporters. Zinc inhibited sugar and amino acid transport in a non-competitive way, without a significant change in the affinity of the transporters for their substrates and with a Vmax decrease. The inhibitory effect of Zn2+ on galactose and phenylalanine uptake was reversed by washing intestinal rings for 5 min with KRT solution. These results suggest that zinc might exert its inhibitory action by a weak binding to chemical groups related with sodium-substrate cotransporters and located in the luminal membrane of the enterocytes.
Lugea
A
A
Departamento de Fisiología y Nutrición, Universidad de Navarra, Pamplona, Spain.
Barber
A
A
Ponz
F
F
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002021:Buffers; D002712:Chlorides / Q000494:pharmacology; D005260:Female; D005690:Galactose / Q000493:pharmacokinetics*; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects; D007583:Jejunum / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D009067:Mouthwashes / Q000494:pharmacology; D010649:Phenylalanine / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D015032:Zinc / Q000494:pharmacology*; D017967:Zinc Compounds / Q000494:pharmacology
D002021:Buffers; D002712:Chlorides; D009067:Mouthwashes; D017967:Zinc Compounds; D010649:Phenylalanine; C016837:zinc chloride; D015032:Zinc; D005690:Galactose