l-Carnitine transport in human placental brush-border membranes is mediated by the sodium-dependent organic cation transporter OCTN2

2004 ◽  
Vol 287 (2) ◽  
pp. C263-C269 ◽  
Author(s):  
Karim Lahjouji ◽  
Ihsan Elimrani ◽  
Julie Lafond ◽  
Line Leduc ◽  
Ijaz A. Qureshi ◽  
...  
Keyword(s):  
Brush Border ◽  
Membrane Vesicles ◽  
Organic Cation Transporter ◽  
Plasma Membrane Vesicles ◽  
Carnitine Transporter ◽  
High Affinity ◽  
Basal Plasma ◽  
Carnitine Transport ◽  
Ph Range ◽  
Carnitine Uptake

Maternofetal transport of l-carnitine, a molecule that shuttles long-chain fatty acids to the mitochondria for oxidation, is thought to be important in preparing the fetus for its lipid-rich postnatal milk diet. Using brush-border membrane (BBM) vesicles from human term placentas, we showed that l-carnitine uptake was sodium and temperature dependent, showed high affinity for carnitine (apparent Km = 11.09 ± 1.32 μM; Vmax = 41.75 ± 0.94 pmol·mg protein−1·min−1), and was unchanged over the pH range from 5.5 to 8.5. l-Carnitine uptake was inhibited in BBM vesicles by valproate, verapamil, tetraethylammonium, and pyrilamine and by structural analogs of l-carnitine, including d-carnitine, acetyl-d,l-carnitine, and propionyl-, butyryl-, octanoyl-, isovaleryl-, and palmitoyl-l-carnitine. Western blot analysis revealed that OCTN2, a high-affinity, Na+-dependent carnitine transporter, was present in placental BBM but not in isolated basal plasma membrane vesicles. The reported properties of OCTN2 resemble those observed for l-carnitine uptake in placental BBM vesicles, suggesting that OCTN2 may mediate most maternofetal carnitine transport in humans.

scholarly journals Characterization of sodium-dependent and sodium-independent nucleoside transport systems in rabbit brush-border and basolateral plasma-membrane vesicles from the renal outer cortex

1989 ◽  
Vol 264 (1) ◽  
pp. 223-231 ◽  
Author(s):  
T C Williams ◽  
A J Doherty ◽  
D A Griffith ◽  
S M Jarvis
Keyword(s):  
Brush Border ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Nucleoside Transport ◽  
Transport Systems ◽  
Facilitated Diffusion ◽  
Basolateral Membrane Vesicles ◽  
Plasma Membrane Vesicles ◽  
Outer Cortex ◽  
Overshoot Phenomenon

The transport of uridine into rabbit renal outer-cortical brush-border and basolateral membrane vesicles was compared at 22 degrees C. Uridine was taken up into an osmotically active space in the absence of metabolism for both types of membrane vesicles. Uridine influx by brush-border membrane vesicles was stimulated by Na+, and in the presence of inwardly directed gradients of Na+ a transient overshoot phenomenon was observed, indicating active transport. Kinetic analysis of the saturable Na+-dependent component of uridine flux indicated that it was consistent with Michaelis-Menten kinetics (Km 12 +/- 3 microM, Vmax. 3.9 +/- 0.9 pmol/s per mg of protein). The sodium:uridine coupling stoichiometry was found to be consistent with 1:1 and involved the net transfer of positive charge. In contrast, uridine influx by basolateral membrane vesicles was not dependent on the cation present and was inhibited by nitrobenzylthioinosine (NBMPR). NBMPR-sensitive uridine transport was saturable (Km 137 +/- 20 microM, Vmax. 5.2 +/- 0.6 pmol/s per mg of protein). Inhibition of uridine flux by NBMPR was associated with high-affinity binding of NBMPR to the basolateral membrane (Kd 0.74 +/- 0.46 nM). Binding of NBMPR to these sites was competitively blocked by adenosine and uridine. These results indicate that uridine crosses the brush-border surface of rabbit proximal renal tubule cells by Na+-dependent pathways, but permeates the basolateral surface by NBMPR-sensitive facilitated-diffusion carriers.

Electrophysiology of plasma membrane vesicles

1984 ◽  
Vol 246 (4) ◽  
pp. F363-F372
Author(s):  
E. M. Wright
Keyword(s):  
Brush Border ◽  
Epithelial Transport ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Tracer Uptake ◽  
Plasma Membrane Vesicles ◽  
Experimental Conditions ◽  
Optical Signals ◽  
Brush Border Membranes ◽  
Vesicle Preparation

In both renal and gastrointestinal physiology, it has become popular to study epithelial transport phenomena using vesicles isolated from the apical and basolateral cell membranes. Transport in vesicle preparations is usually monitored with radioactive tracers, but more recently attention has been directed to electrophysiological methods. As it is impossible to measure the electrical properties of membranes in small vesicles (less than 500 nm diam) with classical electrophysiological techniques, indirect methods have to be employed. In this review I focus on the application of voltage-sensitive optical probes to measure membrane potentials in brush border membrane vesicles. Optical signals are calibrated with diffusion potentials generated with known ion gradients in the presence of ionophores, e.g., EKS with K gradients in the presence of valinomycin. Membrane potential measurements can be used 1) to illustrate the specificity and kinetics of sugar-, amino acid-, and carboxylic acid-Na cotransport systems in brush border membranes, and 2) to determine the ion permeability of brush border membranes. All organic solutes known to be transported by Na cotransport across brush border membranes depolarize the membrane in a Na-dependent, saturable manner. The results agree, both qualitatively and quantitatively, with electrophysiological data obtained in the intact renal tubule and with tracer uptake in vesicles. Bi-ionic potential measurements demonstrate that brush border membranes are permselective to anions and cations, but there are indications that the permeabilities are somewhat dependent on the method of vesicle preparation and the experimental conditions. However, electrical potential measurements provide insight into the mechanisms of ion transport in vesicle preparations, and the application of patch-clamp techniques should provide further gains in the future.

scholarly journals OCTN2-mediated transport of carnitine in isolated Sertoli cells

Reproduction ◽  
2005 ◽  
Vol 129 (6) ◽  
pp. 729-736 ◽  
Author(s):  
Daisuke Kobayashi ◽  
Akihiko Goto ◽  
Tomoji Maeda ◽  
Jun-ichi Nezu ◽  
Akira Tsuji ◽  
...  
Keyword(s):  
Sertoli Cells ◽  
Pcr Analysis ◽  
Rt Pcr ◽  
Carnitine Transporter ◽  
High Affinity ◽  
Carnitine Transport ◽  
Testis Tissue ◽  
Blood Testis Barrier

Carnitine is extensively accumulated in epididymis. Carnitine is also accumulated in testis at higher concentration than in the plasma and is used in spite of the presence of the blood–testis barrier. In this study, we examined the characteristics of carnitine transport in primary-cultured rat Sertoli cells, which constitute a part of the blood–testis barrier. Uptake of [3H]carnitine (11.4 nM) from the basal side of Sertoli cells was Na+-dependent and was significantly decreased in the presence of 10 μM (48.0 ± 7.4% of control) or 100 μM unlabeled carnitine (14.6 ± 5.7% of control). Furthermore, the uptake was significantly inhibited in the presence of 100 μM acetyl-L-carnitine, 100 μM gamma-butyrobetaine or 500 μM quinidine. In RT-PCR analysis, the high-affinity carnitine transporter OCTN2 was detected in rat whole testis tissue and primary-cultured Sertoli cells. In contrast, the low-affinity carnitine transporter ATB0,+was detected in rat whole testis tissue, but not in primary cultured Sertoli cells. These results demonstrate that OCTN2 mediates carnitine supply to Sertoli cells from the circulation.

Uphill transport of beta-alanine in intestinal brush-border membrane vesicles

1990 ◽  
Vol 259 (3) ◽  
pp. G372-G379 ◽  
Author(s):  
Y. Miyamoto ◽  
H. Nakamura ◽  
T. Hoshi ◽  
V. Ganapathy ◽  
F. H. Leibach
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Beta Alanine ◽  
Intestinal Brush Border Membrane ◽  
High Affinity ◽  
Intestinal Brush Border ◽  
Proximal Small Intestine ◽  
Uptake Process

The characteristics of beta-alaline uptake were studied in brush-border membrane vesicles isolated from the proximal small intestine of rabbits and were compared with those of L-alpha-alanine uptake. The uptake of beta-alanine as well as L-alpha-alanine was significantly stimulated by imposing an inwardly directed Na+ gradient. Studies on transstimulation and substrate specificity provide evidence that the transport system serving beta-alanine is distinct from the system serving alpha-alanine. The beta-system also accepts taurine as a substrate. The Na(+)-dependent uptakes of beta-alanine and L-alpha-alanine were differentially influenced by anions. The order in which anions supported uptake was Cl- = SCN- greater than F- greater than NO3- = SO2(-4) for beta-alanine, whereas it was SCN- greater than F- = Cl- = NO3- greater than SO2(-4) for L-alpha-alanine. Cl- appeared to be the preferred anion to support the uptake of beta-alanine. beta-Alanine uptake was greater in the presence of an inwardly directed Cl- gradient than in the presence of Cl- at equal concentrations on both sides of the membrane. The uptake was maximal when a Na+ gradient and a Cl- gradient were present simultaneously. The NaCl gradient-driven beta-alanine uptake was stimulated by an inside-negative K(+)-diffusion potential induced by valinomycin, showing that the uptake process is electrogenic. Stoichiometric analyses suggest that multiple Na+ and one Cl- are associated with the uptake of one beta-alanine molecule. The kinetic study shows that the transporter for beta-alanine is a high-affinity, low-capacity system (Kt = 46 +/- 1 microM; Vmax = 30 +/- 1 pmol.mg protein-1.15 s-1).

scholarly journals Glycine transport into plasma-membrane vesicles derived from rat brain synaptosomes

1981 ◽  
Vol 198 (3) ◽  
pp. 535-541 ◽  
Author(s):  
F Mayor ◽  
J G Marvizón ◽  
M C Aragón ◽  
C Gimenez ◽  
F Valdivieso
Keyword(s):  
Rat Brain ◽  
Membrane Vesicles ◽  
Uptake System ◽  
Plasma Membrane Vesicles ◽  
Glycine Uptake ◽  
High Affinity ◽  
Carbonyl Cyanide ◽  
Brain Synaptosomes ◽  
Glycine Transport ◽  
Sole Energy

1. Transport of glycine has been demonstrated in membrane vesicles isolated from rat brain, using artificially imposed ion gradients as the sole energy source. 2. The uptake of glycine is strictly dependent on the presence of Na+ and Cl- in the medium, and the process can be driven either by an Na+ gradient (out greater than in) or by a C1- gradient (out greater than in) when the other essential ion is present. 3. The uptake of glycine is stimulated by a membrane potential (interior negative), as demonstrated by the effects of the ionophores valinomycin and carbonyl cyanide m-chlorophenylhydrazone and anions of different permeabilities. 4. The kinetic analysis shows that glycine is accumulated by two systems with different affinities. 5. The presence of ouabain, an inhibitor (Na+ + K+)-activated ATPase, does not affect glycine transport. 6. The existence of a high-affinity, Na+-dependent glycine-uptake system in membrane vesicles derived from rat brain suggests that this amino acid may have a transmitter role in some areas of the rat brain.

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