Brush border membrane non-esterified fatty acids. Physiological levels and significance for mucosal iron uptake in mouse proximal intestine

D-Glucose transport was investigated in isolated brush-border membrane vesicles from human small intestine. Characteristics of D-glucose transport from the jejunum were compared with that in the mid and terminal ileum. Jejunal and mid-ileal D-glucose transport was Na+-dependent and electrogenic. The transient overshoot of jejunal D-glucose transport was significantly greater than corresponding values in mid-ileum. The terminal ileum did not exhibit Na+-dependent D-glucose transport, but did exhibit Na+-dependent taurocholate transport. Na+-glucose co-transport activity as measured by tracer-exchange experiments was greatest in the jejunum, and diminished aborally. We conclude that D-glucose transport in man is Na+-dependent and electrogenic in the proximal intestine and directly related to the activity of D-glucose-Na+ transporters present in the brush-border membranes. D-Glucose transport in the terminal ileum resembles colonic transport of D-glucose.

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

Biochemical Journal ◽

10.1042/bj2840877 ◽

1992 ◽

Vol 284 (3) ◽

pp. 877-884 ◽

Cited By ~ 10

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.

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Glycyl-l-proline transport in rabbit enterocyte basolateral-membrane vesicles

Biochemical Journal ◽

10.1042/bj2690565 ◽

1990 ◽

Vol 269 (3) ◽

pp. 565-571 ◽

Cited By ~ 62

Author(s):

J Dyer ◽

R B Beechey ◽

J P Gorvel ◽

R T Smith ◽

R Wootton ◽

...

Keyword(s):

Brush Border ◽

Brush Border Membrane ◽

Membrane Vesicle ◽

Basolateral Membrane ◽

Membrane Vesicles ◽

Peptide Transport ◽

Marker Enzyme ◽

Basolateral Membrane Vesicles ◽

Protein Markers ◽

Proximal Intestine

The properties of a peptide-transport system in rabbit enterocyte basolateral membrane were examined with glycyl-L-proline as the substrate. Basolateral-membrane vesicles prepared from rabbit proximal intestine were characterized in terms of both purity and orientation. Marker-enzyme assays show that the basolateral-membrane marker, ouabain-sensitive K(+)-activated phosphatase, is enriched 17-fold with respect to the initial homogenate. The activities of enzymes used as markers for other membranes and organelles are low, and contamination of the final membrane fraction with these is minimal. The use of immunoblotting techniques further confirms the absence of brush-border-membrane contamination. Proteins in the basolateral-membrane vesicle preparation gave no cross-reaction with antibodies against the 140 kDa antigen and the Na+/glucose-symport protein, markers specific to the brush-border membrane of the enterocyte. Conversely, antibodies raised against the classical basolateral-membrane marker, the RLA class I histocompatibility complex, reacted strongly with a 43 kDa basolateral-membrane protein. The orientation of the basolateral-membrane vesicles was shown to be predominantly inside-out on determination by two independent criteria. The uptake of [1-14C]glycyl-L-proline by these vesicles is stimulated by the presence of an inwardly directed pH gradient, and this stimulation can be abolished by the proton ionophores carbonyl cyanide p-trichloromethoxyphenylhydrazone (CCCP) and tetrachlorotrifluoromethylbenzimidazole (TTFB). Transport is also inhibited by HgCl2, thimerosal, Na+ and other glycyl dipeptides.

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Resection of rabbit ileum: effect on brush border membrane enzyme markers and lipids

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y85-251 ◽

1985 ◽

Vol 63 (12) ◽

pp. 1528-1532 ◽

Cited By ~ 12

Author(s):

M. Keelan ◽

K. Walker ◽

A. B. R. Thomson

Keyword(s):

Fatty Acids ◽

Total Cholesterol ◽

Bile Acids ◽

Chain Length ◽

Brush Border ◽

Brush Border Membrane ◽

Membrane Composition ◽

Rabbit Ileum ◽

Ileal Resection ◽

Distal Small Intestine

Alterations in transport function have been described 6 weeks after surgical resection of 50% of the distal small intestine. Previous studies demonstrated a modest increase in the jejunal uptake of medium chain length fatty acids following resection, while the uptake of many other lipids (cholesterol, bile acids, fatty alcohols, short and long chain length fatty acids) appears to be unaffected. Marked changes in the kinetic constants for the carrier-mediated uptake of four sugars and leucine were observed following resection, but the changes in transport were not associated with changes in the mucosal surface area. This study was undertaken to examine the possible adaptive mechanisms that occur with ileal resection in the rabbit. A 29% increase in the wet weight of jejunal mucosal scrapings and a 53% increase in jejunal brush border membrane (BBM) protein was observed following resection. The jejunal BBM sucrase (S) was unchanged following ileal resection, but alkaline phosphatase (AP) total activities were increased in the resected rabbits. This resulted in a 45% increase in the ratio of AP/S with resection. The lipid composition (total free fatty acids, total bile acids, total cholesterol, total phospholipids, individual phospholipids, and the ratio of total phospholipids/total cholesterol) of BBM was similar in control and resected rabbits. This suggests that quantitative rather than qualitative changes in the membrane composition may be responsible for the transport changes observed in resected animals.

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