Characterization of basolateral membrane Na/H antiport in rat jejunum.
Na uptake studies were performed in order to examine the activity of a Na/H exchanger in basolateral membrane vesicles isolated from rat jejunum. Experiments were carried out under voltage-clamped conditions in order to avoid electrodiffusional ionic movements. 1 mM Na uptake was found to be enhanced by an outward proton gradient and its initial rate was further increased by the presence of monensin or nigericin. The pH gradient-driven Na uptake was inhibited by 2 mM amiloride and unaffected by 0.1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. The initial rate of the proton gradient-induced Na uptake was saturable with respect to external Na, with a Km of 13.6 +/- 1.4 mM and a Vmax of 35.4 +/- 2.2 nmol/mg protein per min. Li competed with Na for the exchange process, whereas K, Rb, Cs, tetramethylammonium had no effect. We conclude that rat jejunal basolateral membrane contains a Na/H exchanger whose properties are similar to those of the antiporter identified in the brush-border membrane.
Orsenigo
M N
MN
Dipartimento di Fisiologia e Biochimica Generali, Università di Milano, Italy.
Tosco
M
M
Zoppi
S
S
Faelli
A
A
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008094:Lithium / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D009550:Nigericin / Q000494:pharmacology; D011522:Protons; D051381:Rats; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D008985:Monensin; D008094:Lithium; D012964:Sodium; D009550:Nigericin