Prolonged hypoxia augments L-citrulline transport by system A in the newborn piglet pulmonary circulation.
OBJECTIVE
Pulmonary arterial endothelial cells (PAECs) express the enzymes needed for generation of l-arginine from intracellular l-citrulline but do not express the enzymes needed for de novo l-citrulline synthesis. Hence, l-citrulline levels in PAECs are dependent on l-citrulline transport. Once generated, l-arginine can be converted to l-citrulline and nitric oxide (NO) by the enzyme NO synthase. We sought to determine whether hypoxia, a condition aetiologically linked to pulmonary hypertension, alters the transport of l-citrulline and the expression of the sodium-coupled neutral amino acid transporters (SNATs) in PAECs from newborn piglets.


RESULTS
PAECs isolated from newborn piglets were cultured under normoxic and hypoxic conditions and used to measure SNAT1, 2, 3, and 5 protein expression and (14)C-l-citrulline uptake. SNAT1 protein expression was increased, while SNAT2, SNAT3, and SNAT5 expression was unaltered in hypoxic PAECs. (14)C-l-citrulline uptake was increased in hypoxic PAECs. Studies with inhibitors of System A (SNAT1/2) and System N (SNAT3/5) revealed that the increased (14)C-l-citrulline uptake was largely due to System A-mediated transport. Additional studies were performed to evaluate SNAT protein expression and l-citrulline levels in lungs of piglets with chronic hypoxia-induced pulmonary hypertension and comparable age controls. Lungs from piglets raised in chronic hypoxia exhibited greater SNAT1 expression and higher l-citrulline levels than lungs from controls.


CONCLUSIONS
Increased SNAT1 expression and the concomitant enhanced ability to transport l-citrulline in PAECs could represent an important regulatory mechanism to counteract NO signalling impairments known to occur during the development of chronic hypoxia-induced pulmonary hypertension in newborns.
Department of Pediatrics, University School of Medicine, Vanderbilt University Medical Center, 2215 B Garland Ave., Nashville, TN 37232-0656, USA. candice.fike@vanderbilt.edu
Candice D
CD
Fike
Marta
M
Sidoryk-Wegrzynowicz
Michael
M
Aschner
Marshall
M
Summar
Lawrence S
LS
Prince
Gary
G
Cunningham
Mark
M
Kaplowitz
Yongmei
Y
Zhang
Judy L
JL
Aschner
D026924:Amino Acid Transport System A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport; D002478:Cells, Cultured; D002908:Chronic Disease; D002956:Citrulline / Q000378:metabolism*; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D065627:Familial Primary Pulmonary Hypertension; D006976:Hypertension, Pulmonary / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D000860:Hypoxia / Q000150:complications / Q000378:metabolism* / Q000503:physiopathology; D049990:Membrane Transport Modulators / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D011651:Pulmonary Artery / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D011652:Pulmonary Circulation; D013552:Swine; D013997:Time Factors
D026924:Amino Acid Transport System A; D049990:Membrane Transport Modulators; D002956:Citrulline; D009569:Nitric Oxide