Characterization of the transport of tri- and dicarboxylates by pig intestinal brush-border membrane vesicles.
1. Transport of citrate and fumarate across the pig intestinal brush-border membrane (BBM) was investigated using isolated BBM vesicles. 2. Citrate and fumarate uptake was stimulated by an inwardly directed Na+ gradient consistent with Na+/citrate (fumarate) co-transport. Cis-inhibition and trans-stimulation experiments strongly suggest the existence of a common transport site for tri- and dicarboxylates. 3. The protonated forms of citrate (citrate-1, citrate-2) seem to be much better transported than citrate-3, indicated by the strong stimulation of citrate uptake at an extravesicular pH of 5.6 compared to pH 7.8. 4. Uptake of tri- and dicarboxylates seems to be potential-sensitive since citrate and in particular fumarate transport was enhanced by an inside negative potential difference. 5. Kinetics of succinate transport revealed a single carrier-mediated component with apparent kinetic constants of 0.43 nmol/mg protein-3 s (Vmax) and 0.14 mmol/l (Km).
Institute of Veterinary Physiology, Zürich, Switzerland.
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S
Wolffram
C
C
Hagemann
B
B
Grenacher
E
E
Scharrer
D000818:Animals; D001692:Biological Transport; D002414:Cations, Monovalent; D002417:Cattle; D002951:Citrates / Q000378:metabolism*; D019343:Citric Acid; D005650:Fumarates / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007583:Jejunum / Q000378:metabolism* / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid; D013552:Swine
D002414:Cations, Monovalent; D002951:Citrates; D005650:Fumarates; D013386:Succinates; D019343:Citric Acid; C032005:fumaric acid; D012964:Sodium; D019802:Succinic Acid