Fig. 7. Proline and betaine transport by Xenopus oocytes expressing mouse SIT1 or PROT. (A,B) Transport characteristics of Xenopus oocytes expressing mouse SIT1. Proline (A) and betaine (B) transport were measured in oocytes expressing SIT1 or in control water-injected oocytes (H₂O) as indicated. The effect of 5 mM betaine (+Bet), histidine (+His) or 2-methylaminoisobutyric acid (+MeAIB) is shown. Bars with different letters (a, b) are significantly different within each panel (P<0.05 by ANOVA and Tukey-Kramer post-hoc test). Each bar represents the mean±s.e.m. of four to seven individual oocytes, except for the water-injected control (n=10). (C,D) Transport characteristics of Xenopus oocytes expressing mouse PROT. Proline (C) and betaine (D) transport were measured in oocytes expressing PROT (labels as in A,B). Since there was no saturable betaine transport (D), competitive inhibitors were not tested for betaine. Each bar represents the mean±s.e.m. of five to eight oocytes, except the water-injected control (n=10). One additional set of injections of PROT was performed (not shown), which confirmed that proline but not betaine uptake was increased in PROT-expressing oocytes as compared with water-injected oocytes (n=5-7 each).