Marginal effect of changes in acid-base status in vitro on rheogenic H+ and HCO3- secretion in turtle urinary bladder

This study systematically evaluates the effect of changes in the acid-base composition of the incubation media on the electrogenic H+ and HCO3- secretion (voltage clamp method and serosal ouabain) in the isolated turtle urinary bladder. Since the various cell types would change their acidity in a similar direction but to a variable degree, measured mean cell pH values (5,5-dimethyl-2,3-oxazolidinedione method) were used for an overall assessment of the changes in the acid-base status of the acid-transporting cells. Although addition of exogenous CO2 (0.7-3%) increased H+ secretion (JH+) 2- to 4-fold from a CO2-free control period, a further increase in the percent of CO2 did not enhance JH+ demonstrating a permissive but not a stimulatory role of CO2. Cyclic AMP plus 3-isobutyl-1-methylxanthine-induced electrogenic HCO3 secretion (JHCO3-) remained unaltered at 10% CO2 from a 5% CO2 control period. Cell acidosis resulting from either alterations in the PCO2/HCO3- levels or from NH4Cl in the bathing solution did not enhance JH+; by contrast maximal levels of acidification were found at cell pH values of about 7.40 and comparable effects on JH+ were found with a variety of PCO2/HCO3- combinations that led to a similar intracellular acidity.