Carrier mediated transport of peptides by the kidney

Small peptide transport was characterized to determine if: (1) Multiple carriers are present in the luminal membrane of renal proximal tubular cells; (2) Carrier-mediated peptide transport is limited by size; and (3) Gentamicin inhibits carrier-mediated reabsorption of peptides.; Uptake of glycyl-({dollar}sp3{dollar}H) proline (Gly-Pro) into renal brush border membrane vesicles demonstrated a dual affinity carrier system (Km{dollar}sb1{dollar} = 1.3 {dollar}times{dollar} 10{dollar}sp{lcub}-2{rcub}{dollar} M, Vmax{dollar}sb1{dollar} = of 4.6 {dollar}times{dollar} 10{dollar}sp{lcub}-9{rcub}{dollar} mol/mg/min and Km{dollar}sb2{dollar} = 2.7 {dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} M, Vmax{dollar}sb2{dollar} = of 7.8 {dollar}times{dollar} 10{dollar}sp{lcub}-11{rcub}{dollar} mol/mg/min). At high concentrations, uptake of Gly-Pro was inhibited by glycyl-sarcosine (Gly-Sar), {dollar}beta{dollar}-ananyl-histidine ({dollar}beta{dollar}-Ala-His), and pyroglutamyl-histidine (pGlu-His). At lower concentrations, uptake of Gly-Pro was competitively inhibited by the dipeptides, glycyl-glycine and Gly-Sar. At both low and high concentrations, coupled cotransport of Gly-Pro with protons was suggested and evidence is presented to indicate that uptake is electrogenic.; Whether multiple carriers are present was further investigated by characterizing the uptake of ({dollar}sp3{dollar}H) pyroglutamyl-histidine (1 {dollar}times{dollar} 10{dollar}sp{lcub}-8{rcub}{dollar} to 1 {dollar}times{dollar} 10{dollar}sp{lcub}-3{rcub}{dollar} M). A dual affinity transport system was observed (Km{dollar}sb1{dollar} = 9.3 {dollar}times{dollar} 10{dollar}sp{lcub}-8{rcub}{dollar} M, Vmax{dollar}sp1{dollar} = 6.1 {dollar}times{dollar} 10{dollar}sp{lcub}-12{rcub}{dollar} mol/mg/min and Km{dollar}sb2{dollar} = 6.3 {dollar}times{dollar} 10{dollar}sp{lcub}-5{rcub}{dollar} M, Vmax{dollar}sb2{dollar} = 2.2 {dollar}times{dollar} 10{dollar}sp{lcub}-9{rcub}{dollar} mol/mg/min). Transport of pGlu-His at high concentrations was inhibited by Gly-Sar, {dollar}beta{dollar}-Ala-His and Gly-Pro, suggesting a common carrier. At lower concentrations, uptake of pGlu-His was not inhibited by Gly-Pro, Gly-Sar, {dollar}beta{dollar}-Ala-His, {dollar}gamma{dollar}-glutamyl-histidine or {dollar}gamma{dollar}-glutamyl-cysteinyl-glycine. Uptake was competitively decreased by pyroglutamyl-alanine. At both low and high concentrations, coupled cotransport of pGlu-His to protons was also shown.; To determine if carrier-mediated transport of peptides is limited by size of the molecule, uptake of the hydrolytically resistant tripeptide, ({dollar}sp3{dollar}H) pryroglutamyl-histidyl-tryptophan (pGlu-His-Trp), and tetrapeptide, ({dollar}sp3{dollar}H) pyroglutamyl-histidyl-tryptophyl-serine (pGlu-His-Trp-Ser) were assessed. No discernable carrier-mediated uptake of these small peptides was observed. This was confirmed by the lack of uptake at 10{dollar}sp{lcub}-6{rcub}{dollar} M over a period of 240 minutes in an inwardly directed hydrogen ion gradient.; These data indicate: Multiple carriers exist on the luminal membrane of renal proximal tubular cells for the transport of dipeptides, and tripeptide pGlu-His-Trp and the tetrapeptide pGlu-His-Trp-Ser (10{dollar}sp{lcub}-9{rcub}{dollar} to 10{dollar}sp{lcub}-6{rcub}{dollar} M) are not taken up by a carrier-mediated mechanism, suggesting that the carrier may be limited by the size of the substrate. (Abstract shortened with permission of author.)...