[Studies on the mechanism of placental transport of L-glutamate (the effect of K+ in microvillous vesicles on L-glutamate uptake)].
The effect of potassium ion and membrane potential on the uptake of L-glutamate in microvilli (brush border) vesicles prepared from human term placenta was studied using a rapid filtration technique. The uptake of L-glutamate into microvilli vesicles is Na+ electrochemical gradient dependent and pre-equilibration of the vesicles with K+ stimulates L-glutamic acid uptake. Imposition of a K+ gradient (K+ in greater than K+ out) enhances Na+-dependent L-glutamate uptake. Changes in membrane potential due to the imposition of anion replacement markedly affect Na+ dependent L-glutamate uptake only in the presence of K+. However, this effect is not significant when changes in membrane potential incur following the imposition of valinomycin induced by K+ diffusion potential. The data indicate that Na+-dependent L-glutamate transport can be additionally energized by a K+ gradient. Furthermore K+ renders Na+-dependent L-glutamate transport sensitive to changes in the transmembrane potential difference.
D002463:Cell Membrane Permeability / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005971:Glutamates / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007477:Ions; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism*; D010920:Placenta / Q000166:cytology; D011188:Potassium / Q000494:pharmacology*; D011247:Pregnancy; D012964:Sodium / Q000502:physiology
D005971:Glutamates; D007477:Ions; D012964:Sodium; D011188:Potassium