Interaction of glycylglycine and Na+ at the mucosal border of guinea-pig small intestine. A non-mutual stimulation of transport.
Sodium-dependence of glycylglycine (Gly-Gly) influx and stimulation of Na+ transport by Gly-Gly were studied in everted sacs, sheet preparations and brush-border membrane vesicles isolated from guinea-pig ileum. Gly-Gly influx was found to be independent of the presence of Na+, while Na+ transport was stimulated by Gly-Gly as evidenced by increases in transmural potential difference (PDt), short-circuit current (Isc) and Na+ influx. The change in PDt (delta PDt) induced by Gly-Gly was a saturable function of Gly-Gly concentration, showing a Michaelis-Menten type relationship. The half-saturation concentration for Gly-Gly estimated from the electrical data was nearly identical with that estimated from influx data. At a constant Gly-Gly concentration the relationship between Isc and Na+ concentration was sigmoid, and the Hill coefficient was 1.5. Kinetic analysis according to Garay and Garrahan indicates that each Gly-Gly carrier has two equivalent non-interacting binding sites for Na+, and that translocation of Na+ occurs when the two Na+ sites on the carrier loaded with Gly-Gly are occupied by Na+. However, our results indicate that the resultant Na+ flow is not capable of stimulating Gly-Gly translocation.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D004151:Dipeptides / Q000378:metabolism*; D005998:Glycine / Q000494:pharmacology; D006033:Glycylglycine / Q000378:metabolism* / Q000494:pharmacology; D006168:Guinea Pigs; D007082:Ileum / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D004151:Dipeptides; D006033:Glycylglycine; D012964:Sodium; D005998:Glycine