Fig. 5. Brefeldin A (BFA) reversibly inhibits development of betaine transport activity after MII oocyte activation. Betaine transport activity in mouse MII oocytes parthenogenetically activated with Sr²⁺ was determined in the presence or absence of BFA. Two separate experiments are shown: (a) 7 and 12 hours and MII oocytes at t=0 (triangle); (b) 10 and 30 hours and MII oocytes (inverted triangle). The results are combined in this figure, but statistical analysis was performed separately. Parthenogenotes were cultured in control medium (black circles) or with BFA (white circles). The dashed arrows indicate the transfer of parthenogenotes from BFA to BFA-free culture at the time indicated by the arrow tail (7 or 10 hours), with betaine transport measured at the time indicated by the arrowhead (12 or 30 hours). Asterisks indicate significant difference from MII oocytes at t=0 (^**P<0.01, ^***P<0.001; ANOVA and Tukey-Kramer post-hoc test). The rates after transfer from BFA (arrows) were not significantly different at 12 hours (white diamond) or 30 hours (white square) from rates after culture in the continuous absence of BFA at the same times (black circles at 12 and 30 hours). Each point is the mean±s.e.m. of three independent measurements of the total rate of betaine transport (non-saturable rate was not subtracted in this set of experiments).