Carrier-mediated L-lactate transport in brush-border membrane vesicles from rat placenta during late gestation.
The mechanism for L-lactate transport across microvillous membrane vesicles prepared from rat placenta was examined. Uptake of L-lactate into these vesicles was mainly the result of transport into the intravesicular (osmotically active) space. The initial rate of L-lactate uptake was not affected by the presence of an inward gradient of either Na+ or K+. In the presence of an inward-directed proton gradient, L-lactate uptake was markedly stimulated, accumulating at concentrations 6-7-fold higher than the equilibrium. Lower transmembrane pH gradients were associated with slower initial uptakes and smaller overshoots. L-Lactate uptake determined under an inside-directed pH gradient was strongly inhibited by p-chloromercuriphenylsulphonic acid, a protein-thiol oxidizing agent. L-Lactate uptake was: (1) saturable as a function of the concentration of L-lactate, (2) inhibited by monocarboxylic acids such as pyruvate, D-lactate, beta-hydroxybutyrate and alpha-cyano-4-hydroxycinnamic acid, and (3) temperature-dependent. When present inside the vesicles, L-lactate, pyruvate and beta-hydroxybutyrate caused trans-stimulation of L-lactate uptake both in the presence and in the absence of an inside-directed pH gradient, indicating that L-lactate transport is a reversible process that can be shared by other monocarboxylic acids. There were no significant changes in maximal initial rate or in the kinetic parameters of L-lactate transport during the last 3 days of gestation.
Alonso de la Torre
S R
SR
Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Salamanca, Spain.
Serrano
M A
MA
Alvarado
F
F
Medina
J M
JM
D002731:4-Chloromercuribenzenesulfonate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002264:Carboxylic Acids / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002412:Cations; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007773:Lactates / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D027501:Monocarboxylic Acid Transporters; D010920:Placenta / Q000378:metabolism* / Q000648:ultrastructure; D011188:Potassium / Q000378:metabolism; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism
D002264:Carboxylic Acids; D002352:Carrier Proteins; D002412:Cations; D007773:Lactates; D008565:Membrane Proteins; D027501:Monocarboxylic Acid Transporters; D002731:4-Chloromercuribenzenesulfonate; D012964:Sodium; D011188:Potassium