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. 1972 Oct;51(10):2653–2662. doi: 10.1172/JCI107083

Carbonic Anhydrase Function and the Epithelial Organization of H+ Secretion in Turtle Urinary Bladder

John H Schwartz 1,2, Seymour Rosen 1,2, Philip R Steinmetz 1,2
PMCID: PMC332964  PMID: 4626848

Abstract

The function of carbonic anhydrase in H+ secretion by the turtle bladder was studied in vitro. Dose response curves were obtained for the carbonic anhydrase inhibitors, acetazolamide and ethoxzolamide, with and without addition of CO2 to the system. In addition, carbonic anhydrase was assayed in homogenates of mucosal cells. The activity in the homogenates was 155±16 U/g dry wt, of which only 11 U represented contamination from erythrocytes; after addition of 5 × 10−6m acetazolamide, no enzyme activity was detectable.

In the intact preparation free of exogenous CO2, the dose response curve for acetazolamide showed two plateaus of inhibition, one at 50% and one at more than 80% inhibition. At 50% inhibition (from 5 × 10−6 to 5 × 10−5m acetazolamide), H+ secretion was restored or enhanced by CO2 addition to the same extent as bladders not exposed to acetazolamide. At concentrations of more than 1 × 10−4m, H+ secretion was no longer restorable by CO2. Unlike acetazolamide, ethoxzolamide caused progressive inhibition of H+ secretion in the CO2-free system. The maximal extent of inhibition with ethoxzolamide and the behavior of inhibition in the presence of 2.5% CO2 were the same as for acetazolamide. Evidence is presented that all surface epithelial cells secrete H+ and generate OH− within the cell interior. The capacity of cells to dispose of OH− by CO2 hydroxylation varies with the availability of cytoplasmic carbonic anhydrase. A small population of cells contains abundant carbonic anhydrase and secretes at high rates even when CO2 is in short supply.

On the basis of these results and histochemical data on the distribution of carbonic anhydrase within the mucosa, an analysis is presented of the epithelial organization of acidification by the turtle bladder.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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