Marginal Effect of Changes in Acid-Base Status in vitro on Rheogenic H⁺ and HCO^-₃ Secretion in Turtle Urinary Bladder

Abstract

This study systematically evaluates the effect of changes in the acid-base composition of the incubation media on the electrogenic H⁺ and HCO^-₃ 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 CCVfree 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-l-methylxanthine-induced electrogenic HCO₃ secretion (JHCO^-₃) remained unaltered at 10% CO₂ from a 5% CO₂ control period. Cell acidosis resulting from either alterations in the PCO₂/HCO^-₃ levels or from NH4CI 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/HCO^-₃ combinations that led to a similar intracellular acidity.