These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Lysine and alanine transport in the perfused guinea-pig placenta.
    Author: Wheeler CP, Yudilevich DL.
    Journal: Biochim Biophys Acta; 1989 Jan 30; 978(2):257-66. PubMed ID: 2492434.
    Abstract:
    The characteristics of L-lysine transport were investigated at brush-border (maternal) and basal (fetal) sides of the syncytiotrophoblast in the term guinea-pig placenta artificially perfused either through the umbilical vessels in situ or through both circulations simultaneously. Cellular uptake, efflux and transplacental transfer were determined using a single-circulation paired-tracer dilution technique. Unidirectional L-[3H]lysine uptake (%) (perfusate lysine 50 microM) was high on maternal (M = 87 +/- 1) and fetal (F = 73 +/- 2) sides. L-[3H]Lysine efflux back into the ipsilateral circulation was asymmetrical (F/M ratio = 2.3) and transplacental flux occurred in favour of the fetal circulation. Unidirectional lysine influx kinetics (0.05-8.00 mM) gave Km values of 1.75 +/- 0.70 mM and 0.90 +/- 0.25 mM at maternal and fetal sides, respectively; corresponding Vmax values were 1.95 +/- 0.38 and 0.87 +/- 0.10 mumol.min-1.g-1. At both sides, lysine influx (50 microM) could be inhibited (about 60-80%) by 4 mM L-lysine and L-ornithine and less effectively (about 10-40%) by L-citrulline, L-arginine, D-lysine and L-histidine. At the basal side: (i) lysine influx kinetics were greatly modified in the presence of 10 mM L-alanine (Km = 6.25 +/- 3.27 mM; Vmax = 2.62 +/- 0.94 mumol.min-1.g-1), but unchanged by equimolar L-phenylalanine or L-tryptophan; (ii) in the converse experiments, lysine (10 mM) did not affect the kinetic characteristics for either L-alanine or L-phenylalanine; (iii) L-lysine and L-alanine influx kinetics were not dependent on the sodium gradient; (iv) the inhibition of L-[3H]lysine uptake by 4 mM L-homoserine was partially (60%) Na+-dependent. At the maternal side the kinetic characteristics for alanine influx were highly Na+-dependent, while lysine influx was partially Na+-dependent only at low concentrations (0.05-0.5 mM). Bilateral perfusion with 2,4-dinitrophenol (1 mM) reduced L-[3H]lysine uptake into the trophoblast and abolished transplacental transfer. It is suggested that lysine transport in the guinea-pig placenta is mediated by a specific transport system (y+) for cationic amino-acids. The asymmetry in the degree of sodium-dependency at both trophoblast membranes may in part explain the maternal-to-foetal polarity of placental amino-acid transfer in vivo.
    [Abstract] [Full Text] [Related] [New Search]