pH dependence of short-circuit current and active phosphate transport by toad bladder

The effect of changing the pH of the mucosal and serosal bathing solutions on active Na transport (estimated by the short-circuit current) and active inorganic phosphate (Pi) transport was studied in the toad bladder. The short-circuit current was unaffected by lowering the pH from 7.6 to 7.1 but was inhibited (29-45%) at pH 6.6, 8.1, 8.6, 9.1, or 9.6. The Pi transport was not changed when the pH was increased from 7.6 to 8.1, but was totally inhibited at pH 6.6, 7.1, 8.6, 9.1 or 9.6. Thus, active transport of Pi occurs only when most of the Pi is HPO4(-2), but the effect of varying pH on active Pi transport in the toad bladder is more complicated than a simple titration of Pi.