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Iodothyronine Interactions with the System L1 Amino Acid Exchanger in 3T3-L1 Adipocytes.

Mitchell FE, Roy LA, Taylor PM - J Thyroid Res (2010)

Bottom Line: Efflux of preloaded L-[(3)H]phenylalanine from 3T3-L1 adipocytes was trans stimulated by external leucine, demonstrating the obligatory exchange mechanism of System L1 transport.T(3) (10 μM) did not significantly trans stimulate L-[(3)H]phenylalanine efflux, but did competitively inhibit the trans stimulatory effect of 10 μM leucine.The results highlight strong competitive interactions between iodothyronines (T(3), rT(3)) and amino acids for transport by System L1 in adipocytes, which may impact cellular iodothyronine exchanges during altered states of protein nutrition.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular Physiology, College of Life Sciences, James Black Centre, University of Dundee, Dundee DD1 5EH, UK.

ABSTRACT
Thyroid hormones enter isolated white adipocytes largely by a System L1-type amino acid transporter en route to exerting genomic actions. Differentiated 3T3-L1 mouse adipocytes in culture express mRNA for LAT1 (the catalytic subunit of high-affinity System L1). L-[(125)I]-T(3) uptake into 3T3-L1 adipocytes included a substantial saturable component inhibited by leucine. L-[(3)H]phenylalanine uptake into 3T3-L1 cells was saturable (K(m) of 31 μM), competitively inhibited by T(3) (K(i) of 1.2 μM) and blocked by leucine, BCH, and rT(3) as expected for substrate interactions of System L1. Efflux of preloaded L-[(3)H]phenylalanine from 3T3-L1 adipocytes was trans stimulated by external leucine, demonstrating the obligatory exchange mechanism of System L1 transport. T(3) (10 μM) did not significantly trans stimulate L-[(3)H]phenylalanine efflux, but did competitively inhibit the trans stimulatory effect of 10 μM leucine. The results highlight strong competitive interactions between iodothyronines (T(3), rT(3)) and amino acids for transport by System L1 in adipocytes, which may impact cellular iodothyronine exchanges during altered states of protein nutrition.

No MeSH data available.


Related in: MedlinePlus

Uptake of the iodothyronine L-T3 into 3T3-L1 adipocytes and pre-adipocytes. [125I]-T3 uptake was measured at 50 nM over 10 minutes in the absence (control) or presence of 10 μM unlabelled T3 or 10 mM leucine in the uptake buffer. Values are expressed ± SEM of 6–12 measurements. *P < .05; value significantly different from control using Dunnett's Multiple Comparison Test.
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fig1: Uptake of the iodothyronine L-T3 into 3T3-L1 adipocytes and pre-adipocytes. [125I]-T3 uptake was measured at 50 nM over 10 minutes in the absence (control) or presence of 10 μM unlabelled T3 or 10 mM leucine in the uptake buffer. Values are expressed ± SEM of 6–12 measurements. *P < .05; value significantly different from control using Dunnett's Multiple Comparison Test.

Mentions: The uptake of 50 nM L-[125I]-T3 into 3T3-L1 adipocytes included a substantial saturable component, being reduced by around 40% on addition of 10 uM unlabelled T3 (Figure 1). The magnitude of this saturable component (approximately 1–1.2 pmol·mg protein−1·10 min−1) was similar in both adipocytes and pre-adipocytes, although total uptake was about 50% higher in pre-adipocytes. An excess of the LNAA leucine (10 mM), inhibited over 80% of saturable T3 uptake (Figure 1). Pre-incubation of 3T3-L1 adipocytes in transport buffer containing 2 mM leucine for 15 minutes (followed by a rapid wash in PBS) resulted in a minor trans stimulatory increase in saturable 50 nM L-[125I]-T3 uptake (by 20 ± 8.5%, n = 3), although this increase did not reach statistical significance.


Iodothyronine Interactions with the System L1 Amino Acid Exchanger in 3T3-L1 Adipocytes.

Mitchell FE, Roy LA, Taylor PM - J Thyroid Res (2010)

Uptake of the iodothyronine L-T3 into 3T3-L1 adipocytes and pre-adipocytes. [125I]-T3 uptake was measured at 50 nM over 10 minutes in the absence (control) or presence of 10 μM unlabelled T3 or 10 mM leucine in the uptake buffer. Values are expressed ± SEM of 6–12 measurements. *P < .05; value significantly different from control using Dunnett's Multiple Comparison Test.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2957699&req=5

fig1: Uptake of the iodothyronine L-T3 into 3T3-L1 adipocytes and pre-adipocytes. [125I]-T3 uptake was measured at 50 nM over 10 minutes in the absence (control) or presence of 10 μM unlabelled T3 or 10 mM leucine in the uptake buffer. Values are expressed ± SEM of 6–12 measurements. *P < .05; value significantly different from control using Dunnett's Multiple Comparison Test.
Mentions: The uptake of 50 nM L-[125I]-T3 into 3T3-L1 adipocytes included a substantial saturable component, being reduced by around 40% on addition of 10 uM unlabelled T3 (Figure 1). The magnitude of this saturable component (approximately 1–1.2 pmol·mg protein−1·10 min−1) was similar in both adipocytes and pre-adipocytes, although total uptake was about 50% higher in pre-adipocytes. An excess of the LNAA leucine (10 mM), inhibited over 80% of saturable T3 uptake (Figure 1). Pre-incubation of 3T3-L1 adipocytes in transport buffer containing 2 mM leucine for 15 minutes (followed by a rapid wash in PBS) resulted in a minor trans stimulatory increase in saturable 50 nM L-[125I]-T3 uptake (by 20 ± 8.5%, n = 3), although this increase did not reach statistical significance.

Bottom Line: Efflux of preloaded L-[(3)H]phenylalanine from 3T3-L1 adipocytes was trans stimulated by external leucine, demonstrating the obligatory exchange mechanism of System L1 transport.T(3) (10 μM) did not significantly trans stimulate L-[(3)H]phenylalanine efflux, but did competitively inhibit the trans stimulatory effect of 10 μM leucine.The results highlight strong competitive interactions between iodothyronines (T(3), rT(3)) and amino acids for transport by System L1 in adipocytes, which may impact cellular iodothyronine exchanges during altered states of protein nutrition.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular Physiology, College of Life Sciences, James Black Centre, University of Dundee, Dundee DD1 5EH, UK.

ABSTRACT
Thyroid hormones enter isolated white adipocytes largely by a System L1-type amino acid transporter en route to exerting genomic actions. Differentiated 3T3-L1 mouse adipocytes in culture express mRNA for LAT1 (the catalytic subunit of high-affinity System L1). L-[(125)I]-T(3) uptake into 3T3-L1 adipocytes included a substantial saturable component inhibited by leucine. L-[(3)H]phenylalanine uptake into 3T3-L1 cells was saturable (K(m) of 31 μM), competitively inhibited by T(3) (K(i) of 1.2 μM) and blocked by leucine, BCH, and rT(3) as expected for substrate interactions of System L1. Efflux of preloaded L-[(3)H]phenylalanine from 3T3-L1 adipocytes was trans stimulated by external leucine, demonstrating the obligatory exchange mechanism of System L1 transport. T(3) (10 μM) did not significantly trans stimulate L-[(3)H]phenylalanine efflux, but did competitively inhibit the trans stimulatory effect of 10 μM leucine. The results highlight strong competitive interactions between iodothyronines (T(3), rT(3)) and amino acids for transport by System L1 in adipocytes, which may impact cellular iodothyronine exchanges during altered states of protein nutrition.

No MeSH data available.


Related in: MedlinePlus