Effect of ouabain on ion transport mechanisms in the isolated turtle bladder

Abstract

Ouabain added to the serosal fluid reduces the net transport of Na to approximately zero, but does not change the net Cl or the net HCO3 flux across short-circuited turtle bladders bathed on both surfaces by Na-Ringer solutions. When transportable anions, Cl and HCO3 are present in the mucosal fluid, ouabain causes a reversal of orientation of ISC [short-circuiting current] and PD [potential difference] such that the serosa becomes electronegative to the mucosa, and the resistance almost doubles. When transportable anions are absent from the mucosal fluid, ouabain causes ISC and PD to reach near zero levels and the resistance doubles. Thus, the ouabain-treated bladders in Na-rich ambient media are indistinguishable from untreated bladders in Na-free (choline) ambient media. Ouabain has no inhibitory effect on the electrical and flux parameters of bladders in Na-free media. Homogenates of bladder wall and of isolated mucosal cells, and microsomal fractions of isolated mucosal cells contain a Na + K-stimulated, ouabain-inhibited ATPase activity. A tentative analysis of the data holds that ouabain attaches in a highly specific manner and with high affinity to a binding site, the integrity of which is critical for Na transport and which is coupled to the ATPase activity of the mucosal cells.