1. Volume 27, Issue 1, Pages 1-10 (January 2006)
Gestational diabetes and the adenosine/l-Arginine/nitric oxide (ALANO) pathway in human umbilical vein endothelium 
R. San Martín, L. Sobrevia 
Placenta 
Volume 27, Issue 1, Pages 1-10 (January 2006)
DOI: /j.placenta
Copyright © 2005 Elsevier Ltd Terms and Conditions

2. Figure 1
Transport and metabolism of l-arginine in endothelial cells. The cationic amino acid l-arginine is taken up by endothelial cells through plasma membrane proteins belonging to systems y+/hCATs (human cationic amino acid transporters), y+L, b0,+ and B0,+. The hCATs transporter expressed in plasma membrane invaginations (i.e. caveolae) in the endothelial cells could be functionally coupled to endothelial nitric oxide synthase (eNOS). l-arginine transported by hCATs is then oxidized by eNOS to l-citrulline generating the co-product nitric oxide (NO). l-citrulline is recycled back to l-arginine in the caveolae via a series of chemical reactions that includes the formation of the intermediary product l-argininosuccinate via argininosuccinate synthetase (ASS) using l-aspartate (Asp) as substrate. The l-argininosuccinate formed in this reaction is metabolised to l-arginine by argininosuccinate lyase (ASL) releasing fumarate (Fum) as a subproduct [68,72]. l-arginine is then metabolised starting a new cycle by eNOS (), or it can be exchanged () with l-arginine that has been taken into the cells through hCATs and other cationic amino acid transport systems (i.e. systems y+L, b0,+ and B0,+) located in different plasma membrane subdomains [28]. This alternative l-arginine pool could be used preferentially for protein synthesis or l-ornithine and urea formation via arginases. l-Ornithine is the substrate for polyamines, l-glutamate or l-proline synthesis.
Placenta  , 1-10DOI: ( /j.placenta )
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3. Figure 2
Effect of gestational diabetes on the adenosine/l-arginine/nitric oxide pathway in human umbilical vein endothelium. Human umbilical vein endothelial cells from gestational diabetic pregnancies show a reduced () adenosine transport activity via hENT1 (human equilibrative nucleoside transporter 1). This effect of gestational diabetes leads to extracellular accumulation and a higher bio-availability of this nucleoside to activate the A2a adenosine receptor subtype. The intracellular signalling cascade triggered by A2a purinoceptor activation by adenosine result in an increased () l-arginine transport activity via human cationic amino acids transporters (hCATs) and increased nitric oxide (NO) synthesis by endothelial NO synthase (eNOS). The intracellular second messengers involved in the effect of adenosine include activation of protein kinase C (PKC) and 42 y 44kDa mitogen-activated protein kinases (p42/44mapk), which then activate (+) l-arginine transport. The upregulation in the endothelial l-arginine/NO pathway by adenosine is associated with an increased transcription of eNOS and SLC7A1 genes leading to increased () eNOS and hCAT-1 mRNA levels, respectively. The increased eNOS expression induced by adenosine is associated with higher levels () of eNOS protein anchored in the caveolae of the endothelial cells. In addition, adenosine also induces serine1177 phosphorylation of eNOS (eNOS∼P) resulting in eNOS activation () and increased () intracellular NO levels. The effect of gestational diabetes on hCAT-1 protein level is unknown in endothelium. The reduced adenosine transport via hENT1 detected HUVEC from gestational diabetes could result from inhibition (–) by PKC, p42/44mapk or NO. Alternatively, the effects of PKC, p42/44mapk or NO could be the result of a lower () transcriptional activity of SLC29A1 gene or mRNA stability leading to a reduced () hENT1 mRNA level. Preliminary result suggests that gestational diabetes is associated with a reduction in the hENT1 protein abundance in HUVEC (R. San Martín and L. Sobrevia, unpublished results). The question mark (?) indicates that the mechanisms leading to decreased hENT1 protein are unknown.
Placenta  , 1-10DOI: ( /j.placenta )
Copyright © 2005 Elsevier Ltd Terms and Conditions