Figure 6.

LAT1 mediates citrulline uptake. Xenopus laevis oocytes were injected with cRNA encoding for LAT1 and the associated glycoprotein 4F2hc and incubated for 2 days to allow for protein expression. Non-injected oocytes served as controls. (A) The uptake of 10 µM [³H]leucine over 15 min was then assessed in the presence or absence of 2 mM unlabeled leucine (Leu) or citrulline (Cit). Basal [³H]leucine uptake measured in control oocytes was subtracted from values obtained with LAT1/4F2hc cRNA-injected oocytes. Data are expressed as percentage of the mean value obtained from leucine uptake into oocytes without any competitive amino acid (11.3 ± 7.2 pmol leucine/oocyte/15 min; n = 16–28). (B) The uptake of 20 µM [¹⁴C]citrulline over 15 min in control oocytes and LAT1/4F2hc cRNA-injected oocytes was determined (mean ± SD, n = 11–12). Statistical calculations were performed with one-way analysis of variance and Tukey’s post hoc test (A) and with t-test (B) (***p < 0.001). (C) Eadie–Hofstee graphical representation of concentration-dependent uptake of [¹⁴C]citrulline over 15 min. Basal [¹⁴C]citrulline uptake in control oocytes was subtracted from values obtained with LAT1/4F2hc cRNA-injected oocytes (mean ± SEM, n = 5–7 oocytes from one frog). Similar results were obtained with oocytes from two other animals.