scholarly journals Alterations in the mucosal processing of iron in response to very-short-term dietary iron depletion and repletion

1992 ◽  
Vol 284 (3) ◽  
pp. 877-884 ◽  
Author(s):  
R W Topham ◽  
C E Eads ◽  
B F Butler
Keyword(s):  
Brush Border ◽  
Iron Uptake ◽  
Brush Border Membrane ◽  
Control Diet ◽  
Membrane Vesicles ◽  
Test Dose ◽  
Brush Border Membrane Vesicles ◽  
Dietary Iron ◽  
Short Term ◽  
Iron Deficient

The transfer of control rats to a low-iron diet for only 24 h resulted in a 2-fold increase in iron uptake by brush-border membrane vesicles. Extension of the low-iron feeding period to 72 h or 2 weeks resulted in only small additional increases in iron uptake by vesicle preparations. In contrast, the transfer of iron-deficient rats to a control diet resulted in a progressive decrease in iron uptake by vesicles that reached a level equivalent to that of control rats in 2 weeks. 59Fe labelling of detergent extracts of these vesicle preparations provided evidence for the presence of an iron-binding protein composed of subunits of 52,000 Da. The changes in the 59Fe labelling of this protein component were consistent with the changes observed in iron uptake by intact brush-border membrane vesicles. The 59Fe-labelling profiles of mucosal ferritin and transferrin from a test dose also were changed substantially in response to very-short-term alterations in dietary iron. Even though changes in dietary iron rapidly altered iron uptake by brush-border membrane vesicles and the incorporation of 59Fe from the test dose into mucosal transferrin, changes in the incorporation of 59Fe into mucosal ferritin best reflected the actual changes in the transfer of iron from dose to plasma.

scholarly journals Influence of lactose on phosphate metabolism in rats

1988 ◽  
Vol 59 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Hanna Dębiec ◽  
Roman Lorenc
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Renal Cortex ◽  
Control Diet ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Male Rats ◽  
Blood Levels ◽  
Phosphate Metabolism ◽  
P Balance

1. Lactose, sucrose or maltose were administered to rats by gavage together with 32PO4, and blood 32P was determined.2. PO4 uptake into blood was increased only when lactose and PO4 were administered into the gut.3. Weaned male rats were fed on a control diet or a diet containing 30, 60 or 120 g lactose/kg. After a 5 d period of adaptation, a 6 d P balance was carried out. After a further 24 d blood levels of PO4, and calcium and PO4 uptake by brush-border membrane vesicles prepared from the renal cortex, were determined.4. The absorption and retention of P were higher in lactose-fed rats. Faecal P excretion decreased with increasing dietary lactose content. Urinary P excretion was lower in the rats fed on 30 and 60 g lactose/kg whereas the 120 g lactose/kg diet increased urinary P.5. Membrane vesicles isolated from rats fed on the diets containing 30 and 60 g lactose/kg showed a higher uptake of PO4, but with the 120 g lactose/kg diet uptake was lower than with membrane vesicles isolated from rats fed on the control diet.6. A statistically significant increase in the serum PO4 level was observed in the rats fed on the diet with 120 g lactose/kg.7. The presence of lactose in the diet caused a stirnulatory effect on PO4 absorption and retention.

Low-affinity transport of pyroglutamyl-histidine in renal brush-border membrane vesicles

1989 ◽  
Vol 257 (5) ◽  
pp. C971-C975 ◽  
Author(s):  
H. A. Skopicki ◽  
K. Fisher ◽  
D. Zikos ◽  
G. Flouret ◽  
D. R. Peterson
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Proximal Tubular Cells ◽  
Tubular Cells ◽  
Luminal Membrane ◽  
Renal Brush Border Membrane ◽  
Proximal Tubular ◽  
Renal Brush Border

These studies were performed to determine if a low-affinity carrier is present in the luminal membrane of proximal tubular cells for the transport of the dipeptide, pyroglutamyl-histidine (pGlu-His). We have previously described the existence of a specific, high-affinity, low-capacity [transport constant (Kt) = 9.3 X 10(-8) M, Vmax = 6.1 X 10(-12) mol.mg-1.min-1] carrier for pGlu-His in renal brush-border membrane vesicles. In the present study, we sought to demonstrate that multiple carriers exist for the transport of a single dipeptide by determining whether a low-affinity carrier also exists for the uptake of pGlu-His. Transport of pGlu-His into brush-border membrane vesicles was saturable over the concentration range of 10(-5)-10(-3) M, yielding a Kt of 6.3 X 10(-5) M and a Vmax of 2.2 X 10(-10) mol.mg-1.min-1. Uptake was inhibited by the dipeptides glycyl-proline, glycyl-sarcosine, and carnosine but not by the tripeptide pyroglutamyl-histidyl-prolinamide. We conclude that 1) pGlu-His is transported across the luminal membrane of the proximal tubule by multiple carriers and 2) the lower affinity carrier, unlike the higher affinity carrier, is nonspecific with respect to other dipeptides.

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