HCO3-Cl exchange transport in the adaptive response to alkalosis by turtle bladder

The isolated turtle urinary bladder acidifies its mucosal (M) solution, and the rate of acidification (JH) is equivalent to the short-circuit current after Na+ transport is abolished by ouabain. When HCO3(-) is present in the serosal solution it is secreted into M in an electroneutral exchange for absorbed Cl-. The rate of HCO3(-) secretion (JHCO3(-)) can be measured by pH stat titration after JH is nullified by an opposing pH gradient. With use of these methods JH and JHCO3 were measured sequentially in bladdes from control animals and animals fed NaHCO3 (alkalosis) or NH4Cl (acidosis). JH in alkalosis (57 +/- 6 micro A) was ot different from control values (53 +/- 7 micro A). JHCO3, however, was nearly 40% higher in alkalosis (1.63 +/- 0.11 vs. 1.17 +/- 0.14 mu mol x h-1 x 8 cm-2). In contrast, JHCO3 in acidosis was similar to control values (0.89 +/- 0.15 mu mol x h-1 x 8 cm-2) but JH was increased. As judged from Cl- fluxes, neither alkalosis nor acidosis altered the electroneutral coupling between HCO3(-) secretion and Cl- absorption. JH and JHCO3 appear to be independent processes in the turtle bladder that are capable of responding independently to physiologic changes in the acid-base status of the intact animal.