Fig. 3. Effects of various inhibitors and inhibitory conditions on tracer Pi uptake in the pyloric caeca of rainbow trout. (A) Experiment 1; (B) experiment 2. Normal (Ringer); Na-choline (Na– free Ringer, Na replaced by choline); Na– KCl (Na-free Ringer, Na replaced by K); Ouabain (Normal plus ouabain, 5 mmol l^–1); P++ (Normal plus 10 mmol l^–1 non-labeled Pi); PFA (Normal plus phosphonoformic acid, trisodium hexahydrate, 5 mmol l^–1); NaN₃ (Normal plus sodium azide, 10 mmol l^–1). Cold [tissues incubated as in Normal but ice-cold (<2°C) medium]. All the tissue incubation media (except P++) contained only tracer Pi (³²P) as the Pi source. Estimated active Pi uptake at tracer Pi concentration was 99.8% of the total uptake. Values are means ± S.E.M. (N=6–8 tissues in A; N=5 tissues in B). Columns with uncommon letters are different (P<0.05) by the Newman–Keuls test. All data were log-transformed before ANOVA. See Materials and methods and Table 1 for the assay procedures.