Fig. 3. (A) A comparison of ammonia flux rates (J_Amm, over 6 h) between epithelia exposed to either symmetrical (L-15 apical/L-15 basolateral; filled columns) or asymmetrical (fresh water apical/L-15 basolateral; open columns) conditions at varying basolateral pH (pH_Bl), total ammonia (T_Amm)=650 µmol l^–1, in series 3. The overall effects of pH and of symmetrical versus asymmetrical conditions were significant (P<0.05). (B) Mean pH gradients and (C) mean P_NH3 gradients associated with these treatments. Values are means +1 S.E.M. (N=6 for all symmetrical groups and N=3 for all asymmetrical groups). Significant differences between specific groups within a treatment (pH_Bl effect) are denoted by different letters; significant differences between specific groups held under either symmetrical or asymmetrical conditions are denoted by an asterisk. 1 nmHg=0.133 Pa.