Fig. 2: Cellular GABA is produced from extracellular ornithine.
From: SLC45A4 encodes a peroxisomal putrescine transporter that promotes GABA de novo synthesis
a GABA synthesis pathways. b 13C5-Glutamine tracing experiment and cellular levels of 13C5-Glutamine, 13C5-Glutamate and 13C4-GABA. c 13C6-Arginine tracing experiment and cellular levels of 13C6-Arginine, 13C5-Ornithine and 13C4-GABA after 13C6-Arginine tracing experiment. d Relative quantification of extracellular ornithine production in fresh RPMI media (Ctr, empty circles) or containing 10% fetal bovine serum (Serum, full circles). e Ornithine levels after 24 h in RPMI media containing 10% of control fetal bovine serum (Control FBS) or after heat-inactivation (Heated FBS). f Simultaneous labeling of GABA from 1.15 mM 13C6-arginine and 0.2 mM 2H6-ornithine in A549 cells cultured heat-inactivated dialyzed FBS (hiFBS). g Cellular 2H6-GABA levels in HepG2 cells overexpressing empty vector (Ctr) or SLC45A4 and cultured with 10% hiFBS and 0.2 mM 2H6-ornithine. In all figures, data are mean ± SEM; n = 3 biological independent replicates. **P < 0.01; *P < 0.05; ns, not significant by one-sided unpaired Student’s t-test. The p-value in (g). is p = 0,00006. Source data are provided as Source Data file.
