Fig. 1. Betaine and proline transport activity in mouse oocytes and preimplantation embryos. (A) Total and non-saturable betaine transport. The total rate of 1 µM [³H]betaine transport at each stage (labeled at bottom of figure) is indicated by the black bars, and the nonspecific, non-saturable rate (with 5 mM unlabeled betaine) by the gray bars. Total betaine transport was significantly different from non-saturable transport at stages indicated by asterisks (^*P<0.05, ^***P<0.001 within stages, by Student's t-test). Each bar represents the mean±s.e.m. of at least three independent measurements. (B) Specific betaine transport. Data in A were used to obtain the rate of specific betaine transporter activity by subtracting the mean non-saturable transport from the total transport at each stage. Bars labeled with different letters are significantly different from each other (P<0.05 by ANOVA and Tukey-Kramer post-hoc test). (C) Specific proline transport. Specific transport of 1 µM [³H]proline was calculated as for betaine. Each bar represents the mean±s.e.m. of at least three independent measurements. nd, not determined.