Fig. 6. Permeability to glycine induced by hypotonic swelling in embryos. Glycine permeability was determined by exposing 1-cell (1c), 2-cell (2c), or 4-cell (4c) embryos to [³H]glycine for 15 minutes, and then measuring total accumulated glycine (see text). Tonicity of the solution is specified in the key. Data are normalized to the mean glycine accumulation at 285 mOsM under each condition, arbitrarily set to one. DIDS completely blocked the swelling-induced component of glycine permeability in interphase 2-cell embryos as shown by the labeled bar. Two cell embryos in late G₂ were either arrested by cycloheximide (cyclohex) or measured in embryos obtained as close to entry into prophase as possible. 1-cell and 2-cell embryos in metaphase were either arrested with demecolcine (deme) or measurements made during metaphase. Significant differences in glycine permeability between hypotonically swollen embryos versus embryos in 285 mOsM medium are indicated by letters (a, a': P<0.0001; b: P<0.0005; c: P<0.001; d: P<0.005; e: P=0.02; NS: P=0.56; a' indicates significant difference in the presence of DIDS versus without DIDS). The number of replicates (each replicate a group of 5-10 embryos) was 7-10 for each treatment, except only 5 replicates of 2-cell embryos in metaphase were obtained. Interphase 2-cell embryos were included in several separate experiments (total of 21 replicates at 285 mOsM and 29 at 185 mOsM); the data obtained in separate experiments were not significantly different and thus are pooled for presentation. However, statistical significance as shown was determined for differences between groups within the same experiment (e.g., for 185 mOsM versus 185+DIDS).