Fig. 1. (A) Transepithelial resistance (TER) of cultured epithelia before (symmetrical conditions, L-15 apical/L-15 basolateral) and after (asymmetrical conditions, fresh water apical/L-15 basolateral) the addition of apical fresh water at three different basolateral concentrations of total ammonia (T_Amm) in series 1. Values are means +1 S.E.M. (N=10 per group). All increases in TER were highly significant (P<0.001), but there were no significant differences (P>0.05) associated with different T_Amm levels. (B) Ammonia flux rates (J_Amm) from basolateral-to-apical compartments under asymmetrical conditions over a 3 h flux period at the three different basolateral T_Amm levels in the same preparations. An asterisk denotes a statistically significant difference (P<0.05) from the 123 µmol l^–1 group and a double dagger denotes a statistically significant difference (P<0.05) from both other groups. (C) Relationships between J_Amm and TER in individual cultured epithelia under asymmetrical conditions in each of the three groups in B. The regression equations are as follows. At 123 µmol l^–1, filled circles, J_Amm=–0.103TER+6.593, r=0.33, N=10, P>0.05; at 400 µmol l^–1, open circles, J_Amm=–0.176TER+10.495, r=0.49, N=10, P>0.05; at 1055 µmol l^–1, open squares, J_Amm=–0.924TER+22.483, r=0.90, N=10, P<0.0001.

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