Acidification of mucosal fluid by transport of bicarbonate ion in turtle bladders

Abstract

The mucosal fluid of the isolated bladder of Pseudemys scripta is apparently acidified by the active transport of bicarbonate in the ionic form from the mucosal to the serosal fluid. This acidification process, independent of carbonic anhydrase activity, occurs concomitantly with the net transfer of Na+ and C1 from the mucosal to the serosal fluid. In bladders filled with NaHCO3 and NaCl mixtures and bathed in large volumes of soidum-Ringer solution, the pH of the limited volume of mucosal fluid decreases from initial levels of 6.0-7.0 to final levels of approximately 4.0. Concomitantly, the concentration of free CO2 decreases to values of half those in the serosal fluid; and concentrations of bicarbonate approach values of about 1/1000 of those in the serosal fluid. The transbladder gradient of bicarbonate is greater than that expected from observed transbladder potentials. No evidence is found for the presence of materials which absorb CO2. These data are inconsistent with hypotheses holding that acidification is due to a secretion of H+ ion alone or in conjunction with a cellular sink for CO2.