The Karner lab is supported by National Institute of Health R01 grants (AR076325 and AR071967) to C.M.K.

All mouse procedures described herein were approved by the Animal Studies Committees at the University of Texas Southwestern Medical Center at Dallas. The radiation protocol was approved by the Radiation Safety Advisory Committee at the University of Texas Southwestern Medical Center at Dallas.
1. Amino acid uptake in cells (Protocol I)
<ol>
	<li>Plate 5 x 104 ST2 cells in each well of a 12-well tissue culture plate. Plate cells in &#945;-MEM containing 10% FBS, 1...

<ol>
	<li>Xiao, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+&#945;-KG-dependent+histone+and+DNA+demethylases+by+fumarate+and+succinate+that+are+accumulated+in+mutations+of+FH+and+SDH+tumor+suppressors.">Inhibition of &#945;-KG-dependent histone and DNA demethylases by fumarate and succinate that are accumulated in mutations of FH and SDH tumor suppressors.</a> Genes &amp; Development. 26 (12), 1326-1338 (2012).</li><li>Altman, B. J., Stine, Z. E., Dang, C. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+Krebs+to+clinic:+glutamine+metabolism+to+cancer+therapy.">From Krebs to clinic: glutamine metabolism to cancer therapy.</a> Nature Reviews Cancer. 16 (10), 619-634 (2016).</li><li>Karner, C. M., Long, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wnt+signaling+and+cellular+metabolism+in+osteoblasts.">Wnt signaling and cellular metabolism in osteoblasts.</a> Cell and Molecular Life Sciences. 74 (9), 1649-1657 (2017).</li><li>Zarse, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impaired+insulin/IGF1+signaling+extends+life+span+by+promoting+mitochondrial+L-proline+catabolism+to+induce+a+transient+ROS+signal.">Impaired insulin/IGF1 signaling extends life span by promoting mitochondrial L-proline catabolism to induce a transient ROS signal.</a> Cell Metabolism. 15 (4), 451-465 (2012).</li><li>Nagano, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proline+dehydrogenase+promotes+senescence+through+the+generation+of+reactive+oxygen+species.">Proline dehydrogenase promotes senescence through the generation of reactive oxygen species.</a> Journal of Cell Science. 130 (8), 1413-1420 (2017).</li><li>Comes, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=L-Proline+induces+a+mesenchymal-like+invasive+program+in+embryonic+stem+cells+by+remodeling+H3K9+and+H3K36+methylation.">L-Proline induces a mesenchymal-like invasive program in embryonic stem cells by remodeling H3K9 and H3K36 methylation.</a> Stem Cell Reports. 1 (4), 307-321 (2013).</li><li>Fan, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glutamine-driven+oxidative+phosphorylation+is+a+major+ATP+source+in+transformed+mammalian+cells+in+both+normoxia+and+hypoxia.">Glutamine-driven oxidative phosphorylation is a major ATP source in transformed mammalian cells in both normoxia and hypoxia.</a> Molecular Systems Biology. 9, 712 (2013).</li><li>Hosios, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amino+acids+rather+than+glucose+account+for+the+majority+of+cell+mass+in+proliferating+mammalian+cells.">Amino acids rather than glucose account for the majority of cell mass in proliferating mammalian cells.</a> Developmental Cell. 36 (5), 540-549 (2016).</li><li>Welbourne, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ammonia+production+and+glutamine+incorporation+into+glutathione+in+the+functioning+rat+kidney.">Ammonia production and glutamine incorporation into glutathione in the functioning rat kidney.</a> Canadian Journal of Biochemistry. 57 (3), 233-237 (1979).</li><li>Sullivan, L. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Supporting+aspartate+biosynthesis+is+an+essential+function+of+respiration+in+proliferating+cells.">Supporting aspartate biosynthesis is an essential function of respiration in proliferating cells.</a> Cell. 162 (3), 552-563 (2015).</li><li>Nelsen, C. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amino+acids+regulate+hepatocyte+proliferation+through+modulation+of+cyclin+D1+expression.">Amino acids regulate hepatocyte proliferation through modulation of cyclin D1 expression.</a> The Journal of Biological Chemistry. 278 (28), 25853-25858 (2003).</li><li>Krall, A. S., Xu, S., Graeber, T. G., Braas, D., Christofk, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asparagine+promotes+cancer+cell+proliferation+through+use+as+an+amino+acid+exchange+factor.">Asparagine promotes cancer cell proliferation through use as an amino acid exchange factor.</a> Nature Communications. 7, 11457 (2016).</li><li>Green, C. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Branched-chain+amino+acid+catabolism+fuels+adipocyte+differentiation+and+lipogenesis.">Branched-chain amino acid catabolism fuels adipocyte differentiation and lipogenesis.</a> Nature Chemical Biology. 12 (1), 15-21 (2016).</li><li>Shiraki, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methionine+metabolism+regulates+maintenance+and+differentiation+of+human+pluripotent+stem+cells.">Methionine metabolism regulates maintenance and differentiation of human pluripotent stem cells.</a> Cell Metabolism. 19 (5), 780-794 (2014).</li><li>Yu, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glutamine+metabolism+regulates+proliferation+and+lineage+allocation+in+skeletal+stem+cells.">Glutamine metabolism regulates proliferation and lineage allocation in skeletal stem cells.</a> Cell Metabolism. 29 (4), 966-978 (2019).</li><li>Shen, L., Sharma, D., Yu, Y., Long, F., Karner, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biphasic+regulation+of+glutamine+consumption+by+WNT+during+osteoblast+differentiation.">Biphasic regulation of glutamine consumption by WNT during osteoblast differentiation.</a> Journal of Cell Science. 134 (1), (2021).</li><li>Karner, C. M., Esen, E., Okunade, A. L., Patterson, B. W., Long, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+glutamine+catabolism+mediates+bone+anabolism+in+response+to+WNT+signaling.">Increased glutamine catabolism mediates bone anabolism in response to WNT signaling.</a> Journal of Clinical Investigation. 125 (2), 551-562 (2015).</li><li>Hu, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+amino+acid+sensor+Eif2ak4/GCN2+is+required+for+proliferation+of+osteoblast+progenitors+in+mice.">The amino acid sensor Eif2ak4/GCN2 is required for proliferation of osteoblast progenitors in mice.</a> Journal of Bone and Mineral Research. 35 (10), 2004-2014 (2020).</li><li>Rached, M. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FoxO1+is+a+positive+regulator+of+bone+formation+by+favoring+protein+synthesis+and+resistance+to+oxidative+stress+in+osteoblasts.">FoxO1 is a positive regulator of bone formation by favoring protein synthesis and resistance to oxidative stress in osteoblasts.</a> Cell Metabolism. 11 (2), 147-160 (2010).</li><li>Elefteriou, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ATF4+mediation+of+NF1+functions+in+osteoblast+reveals+a+nutritional+basis+for+congenital+skeletal+dysplasiae.">ATF4 mediation of NF1 functions in osteoblast reveals a nutritional basis for congenital skeletal dysplasiae.</a> Cell Metabolism. 4 (6), 441-451 (2006).</li><li>Maleknia, S. D., Johnson, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass+spectrometry+of+amino+acids+and+proteins.">Mass spectrometry of amino acids and proteins.</a> Amino Acids, Peptides and Proteins in Organic Chemistry. , 1-50 (2011).</li><li>Rennie, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+introduction+to+the+use+of+tracers+in+nutrition+and+metabolism.">An introduction to the use of tracers in nutrition and metabolism.</a> The Proceedings of the Nutrition Society. 58 (4), 935-944 (1999).</li><li>Hahn, T. J., Downing, S. J., Phang, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amino+acid+transport+in+adult+diaphyseal+bone:+contrast+with+amino+acid+transport+mechanisms+in+fetal+membranous+bone.">Amino acid transport in adult diaphyseal bone: contrast with amino acid transport mechanisms in fetal membranous bone.</a> Biochimica Biophysica Acta. 183 (1), 194-203 (1969).</li><li>Rosenbusch, J. P., Flanagan, B., Nichols, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Active+transport+of+amino+acids+into+bone+cells.">Active transport of amino acids into bone cells.</a> Biochimica Biophysica Acta. 135 (4), 732-740 (1967).</li><li>Kandasamy, P., Gyimesi, G., Kanai, Y., Hediger, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amino+acid+transporters+revisited:+New+views+in+health+and+disease.">Amino acid transporters revisited: New views in health and disease.</a> Trends in Biochemical Sciences. 43 (10), 752-789 (2018).</li></ol>

The authors have no disclosures.

The protocol described herein provides a fast and sensitive approach to evaluate amino acid uptake in response to various experimental permutations either in vitro or ex vivo. When compared to commercially available kits (e.g., Glutamine and Glutamate Determination Kit), this method is much more sensitive, quicker, and less labor intensive16,17,25. In our protocol, we evaluate uptake in the Krebs Ringers HEPES ...

Amino acids are organic compounds that contain an amino (-NH2) and carboxyl (-COOH) functional groups with a variable side chain that is specific to each amino acid. In general, amino acids are well known as the basic constituent of protein. More recently, novel uses, and functions of amino acids have been elucidated. For example, individual amino acids can be metabolized to generate intermediate metabolites that contribute to bioenergetics, function as enzymatic cofactors, regulate reactive oxygen species or are used to synthesize other amino acids1,2,3,4,5,6,7,8,9,10. Many studies demonstrate that amino acid metabolism is critical for cell pluripotency, proliferation, and differentiation in various contexts3,6,11,12,13,14,15,16,17.
Osteoblasts are secretory cells that produce and secrete the Collagen Type 1 rich extracellular bone matrix. To sustain high rates of protein synthesis during bone formation, osteoblasts demand a constant supply of amino acids. To meet this demand, osteoblasts must actively acquire amino acids. Consistent with this, recent studies reveal the importance of amino acid uptake and metabolism in osteoblast activity and bone formation15,16,17,18,19,20.
Osteoblasts acquire cellular amino acids from three major sources: extracellular milieu, intracellular protein degradation and de novo amino acid biosynthesis. This protocol will focus on the evaluation of amino acid uptake from extracellular environment. The most common methods to measure amino acid uptake rely on either radiolabeled (e.g., 3H or 14C) or heavy isotope labeled (e.g., 13C) amino acids. Heavy isotopomer assays can analyze amino acid uptake and metabolism more thoroughly and safely but are more time consuming taking multiple days to complete as it takes a day to prepare and derivatize samples and multiple days to analyze on the mass spectrometer depending on the number of samples21,22. By comparison, radiolabeled amino acid uptake assays are not informative about downstream metabolism but are cheap and relatively fast, being able to be completed within 2-3 h from the start of the experiment23,24. Here, we describe an easily modifiable basic protocol designed to evaluate radiolabeled amino acid uptake in cultured primary cells or cell lines in vitro or individual bone shafts ex vivo. The application of these two protocols can be extended to other radiolabeled amino acids and other bone associated cell types and tissues.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.25% trypsin</td>
			<td>Gibco</td>
			<td>25200</td>
			<td></td>
		</tr>
		<tr>
			<td>12-well plate</td>
			<td>Corning</td>
			<td>3513</td>
			<td></td>
		</tr>
		<tr>
			<td>1mL syringe</td>
			<td>BD precision</td>
			<td>309628</td>
			<td></td>
		</tr>
		<tr>
			<td>30G Needle</td>
			<td>BD precision</td>
			<td>305106</td>
			<td></td>
		</tr>
		<tr>
			<td>Arginine Monohydrochloride L-[2,3,4-3H]-, 1mCi</td>
			<td>PerkinElmer</td>
			<td>NET1123001MC</td>
			<td></td>
		</tr>
		<tr>
			<td>Beckman LS6500 scintillation counter</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride</td>
			<td>Sigma</td>
			<td>C1016</td>
			<td></td>
		</tr>
		<tr>
			<td>choline chloride</td>
			<td>Sigma</td>
			<td>C7077</td>
			<td></td>
		</tr>
		<tr>
			<td>D-(+)-Glucose solution</td>
			<td>Sigma</td>
			<td>G8769</td>
			<td></td>
		</tr>
		<tr>
			<td>Dissection Tool</td>
			<td></td>
			<td></td>
			<td>Forceps, scissors, scapels</td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Gibco</td>
			<td>14190</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylenediaminetetraacetic acid</td>
			<td>Sigma</td>
			<td>E9884</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES(1M)</td>
			<td>Gibco</td>
			<td>15630</td>
			<td></td>
		</tr>
		<tr>
			<td>L-[3,4-3H(N)]-Glutamine</td>
			<td>PerkinElmer</td>
			<td>NET551250UC</td>
			<td></td>
		</tr>
		<tr>
			<td>Liquid scintilation vials</td>
			<td>Sigma</td>
			<td>Z190535</td>
			<td></td>
		</tr>
		<tr>
			<td>lithium chloride solution, 8M</td>
			<td>Sigma</td>
			<td>L7026</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td>Sigma</td>
			<td>M8266</td>
			<td></td>
		</tr>
		<tr>
			<td>MEM&#945;</td>
			<td>Gibco</td>
			<td>12561</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge tube, 15mL</td>
			<td>Biotix</td>
			<td>89511-256</td>
			<td></td>
		</tr>
		<tr>
			<td>NP-40</td>
			<td>Sigma</td>
			<td>492016</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Sigma</td>
			<td>P3911</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma</td>
			<td>S6014</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium chloride</td>
			<td>Sigma</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Deoxycholate</td>
			<td>Sigma</td>
			<td>D6750</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate</td>
			<td>Sigma</td>
			<td>436143</td>
			<td></td>
		</tr>
		<tr>
			<td>Sonicator</td>
			<td>Sonic&#38;Materials</td>
			<td>VCX130</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris Base</td>
			<td>Sigma</td>
			<td>648311</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultima Gold (Scintillation solution)</td>
			<td>PerkinElmer</td>
			<td>6013329</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-(Methylamino)isobutyric acid</td>
			<td>Sigma</td>
			<td>M2383</td>
			<td></td>
		</tr>
	</tbody>
</table>

evaluation of amino acid consumption in cultured bone cells and isolated bone shafts

Bone development and homeostasis is dependent upon the differentiation and activity of bone forming osteoblasts. Osteoblast differentiation is sequentially characterized by proliferation followed by protein synthesis and ultimately bone matrix secretion. Proliferation and protein synthesis require a constant supply of amino acids. Despite this, very little is known about amino acid consumption in osteoblasts. Here we describe a very sensitive protocol that is designed to measure amino acid consumption using radiolabeled amino acids. This method is optimized to quantify changes in amino acid uptake that are associated with osteoblast proliferation or differentiation, drug or growth factor treatments, or various genetic manipulations. Importantly, this method can be used interchangeably to quantify amino acid consumption in cultured cell lines or primary cells in vitro or in isolated bone shafts ex vivo. Finally, our method can be easily adapted to measure the transport of any of the amino acids as well as glucose and other radiolabeled nutrients.

Amino acid transport is regulated by many membrane-bound amino acid transporters that have been categorized into distinct transport systems based on numerous characteristics, including substrate specificity, kinetics, as well as ion and pH dependence25. For example, glutamine uptake can be mediated by the Na+-dependent transport systems A, ASC, &#947;+L and N or the Na+-independent System L. The Na+-dependent systems are distinguished by the ability to substitute L...

Watch this Scientific Journal Video about Evaluation of Amino Acid Consumption in Cultured Bone Cells and Isolated Bone Shafts at JoVE.com

Evaluation of Amino Acid Consumption in Cultured Bone Cells and Isolated Bone Shafts

This protocol presents a radiolabeled amino acid uptake assay, which is useful for evaluating amino acid consumption either in primary cells or in isolated bones.

Bone development and homeostasis is dependent upon the differentiation and activity of bone forming osteoblasts. Osteoblast differentiation is ...

Amino acid uptake and metabolism are essential for osteoblast specification, differentiation, and bone formation. This protocol provides a rapid and sensitive method to evaluate amino acid uptake. Our protocol uses radiolabeled amino acids to quantify amino acid uptake.It is a cheap, sensitive and a fast method which can be easily modified for different conditions. This protocol can easily be modified to evaluate the uptake of other radiolabeled nutrients like glucose and fatty acids in a variety of tissues as well as primary or transform cells. To begin amino acid uptake assay plate five times 10 to the fourth ST2 cells in each well of a 12 well tissue culture plate in alpha MEM medium supplemented with FBS, penicillin and streptomycin.Plate extra wells of cells to quantify the cell number per condition for the normalizations. Next, incubate cells in a humidified cell culture incubator at 37 degrees Celsius with 5%carbon dioxide for two to three days until confluent. After incubation aspirate the medium and wash the cells twice with one milliliter of PBS at pH 7.4.Then aspirate the PBS before washing the cells once with one milliliter Krebs-Ringer's HEPES or KRH. Incubate cells with 0.5 milliliters of freshly prepared KRH containing four microcuries per milliliter L34 tritiated glutamine working media for five minutes. Post incubation, collect the radioactive medium to dispense into the liquid waste container.Then wash the cells three times with ice cold KRH to terminate the reaction. Next, add one milliliter of 1%sodium dodecyl sulfate to each well and triturate the mixture 10 times to lyse and homogenize the cells. Then transfer the cell lysates to a 1.5 milliliter tube and clarify the lysate by centrifuging at a minimum speed of 10, 000 G for 10 minutes.Transfer the supernatant to a scintillation vial containing eight milliliters of the scintillation solution, and read radio activity and counts per minute using the scintillation counter. From the remaining non-radioactive plates of cells, trypsinize, resuspend, and count the cells to estimate the number of cells in the lysed radioactive cultures. Using a hemacytometer, count the number of cells per non-radioactive well for each experimental condition.To determine amino acid uptake, flush out the marrow from the bone before weighing the bone shaft. To decellularize the bone, boil one humerus in PBS at 100 degrees Celsius for 10 minutes. Equilibrate both live and boiled humeri in one milliliter of KRH for 30 minutes in the cell culture incubator at 37 degrees Celsius.Next, incubate the experimental and boiled control bones separately in freshly prepared KRH containing four microcurries per milliliter L234 triciated arginine for up to 90 minutes at 37 degrees Celsius. After removing the radioactive medium, terminate the reaction by washing humerus three times with one milliliter of ice cold KRH. Transfer each bone into a 1.5 milliliter tube with 500 microliters of RIPA Buffer.Then homogenize the humerus and RIPA Buffer by chopping 100 times with scissors, followed by sonication at 35%amplitude and one second pulse for 10 seconds. Clarified the lysate by centrifugation for 10 minutes at 10, 000 times G at room temperature. Post centrifugation, transfer 200 microliters of the supernatant to scintillation vials containing eight milliliters of the scintillation solution.Read radio activity using the scintillation counter. Kinetic properties of in vitro L34 tritiated glutamine uptake and confluent ST2 cells were evaluated in the presence or absence of sodium methyl amino isobutyric acid or lithium. The removal of sodium led to a 90%reduction in glutamine uptake.The presence of lithium increased glutamine uptake by 2%compared to the sodium free condition. Whereas methyl amino isobutyric acid did not affect glutamine uptake. The estimation percentage contributions of system A, N, L or ASC and gamma plus L indicated that most glutamine uptake is mediated by systems ASC and gamma plus L.System N is responsible for roughly 2%sodium dependent glutamine uptake.And system A showed 0%contribution and uptake. X-VIVO L34 tritiated arginine uptake in boiled and live neonatal humeri was analyzed over a time course of two hours. Arginine uptake increased linearly throughout the experiment and live humeri.The boiled humeri did not exhibit a dynamic increase of arginine uptake in the experiment. The representative analysis shows the normalized and corrected arginine uptake. It is important to boil the contralateral bone as a active control.This step is essential as the bone matrix may absorb radioactive amino acids, resulting in inaccurate results. The protocol has allowed us to confirm amino acid uptake kinetics both in vitro and in vivo.

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1.7K Views.  University of Texas Southwestern Medical Center. Amino acid uptake and metabolism are essential for osteoblast specification, differentiation, and bone formation. This protocol provides a rapid and sensitive method to evaluate amino acid uptake. Our protocol uses radiolabeled amino acids to quantify amino acid uptake.It is a cheap, sensitive and a fast method which can be easily modified for different conditions. This protocol can easily be modified to evaluate the uptake of other radiolabeled nutrients like glucose and fatty acids i...