Influence of transepithelial potential difference on acidification in the toad urinary bladder

The rate of urinary acidification by toad urinary bladders was measured in vitro by following the pH changes of the HCO3-/CO2-buffered Ringer's solutions bathing the mucosal and serosal sides of the bladder. Within the tolerated range of transepithelial potential differences (PD) (-100 to +100 mv), the rate of acidification was found to be a linear function of the PD. The rate of acidification could be increased by a favorable PD whether the PD was the spontaneous transepithelial PD due to sodium transport or a PD imposed in the absence of sodium transport, as when choline was substituted for Na or when amiloride blocked sodium transport. Acetazolamide inhibited both active and PD-driven acidification. Acidification rate was the same in 2.4 mM HCO3- and 1% CO2 as in 12 mM HCO3- and 5% CO2; again, acidification was increased equally by a favorable PD. PD-driven acidification was found to be linearly correlated with acidification occurring at short-circuit conditions. These findings suggest that the rate of acidification can be accelerated by the transepithelial PD in the absence of sodium transport and that the PD-driven component of acidification utilizes a transcellular pathway.