Characteristics of glycyl-L-proline transport in intestinal brush-border membrane vesicles.
A proton-peptide symport mechanism has been postulated for transport of dipeptides in rabbit intestinal and renal brush-border membrane vesicles (BBMV). We have investigated the effects of a transmembrane potential (in mouse) and an inwardly directed proton gradient (in mouse, rabbit, and human) on the transport of glycyl-L-proline in intestinal BBMV. Membrane potential alterations, induced by permeant anions or generated by a K+-diffusion potential in the presence of valinomycin, did not accelerate the uptake of glycyl-L-proline. In contrast, in parallel experiments the uptake of D-glucose, whose cotransport system is electrogenic, was markedly increased by an interior negative membrane potential. Thus the transport of glycyl-L-proline in mouse intestinal BBMV is not electrogenic. Further studies on the effect of a proton gradient (extravesicular pH 5.5; intravesicular pH 7.5) on transport of glycyl-L-proline revealed an absence of stimulation of glycyl-L-proline transport and lower uptake rates in the presence of a proton gradient. The simultaneous presence of an interior negative membrane potential and an inwardly directed proton gradient did not accelerate the transport of glycyl-L-proline. These results demonstrate that the transport of glycyl-L-proline in mouse intestinal BBMV is neither electrogenic nor energized by an inwardly directed proton gradient. Likewise, pH gradients do not stimulate glycyl-L-proline uptake in either rabbit or human BBMV.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004058:Diffusion; D004151:Dipeptides / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000648:ultrastructure*; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D008871:Microvilli / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011522:Protons; D011817:Rabbits
D004151:Dipeptides; D011522:Protons; C015248:glycylproline; D005947:Glucose; D011188:Potassium