Carbonic anhydrase inhibition and cell volume regulation in Necturus gallbladder

Gallbladder epithelial cells transport salt and water isotonically as the renal proximal tubule. The cells also have the property of regulating their cell volume in response to osmotic stress (Fisher et al. 1981, Persson & Spring 1982, Fisher & Spring 1984, Foskett & Spring 1985). The volume-regulating phenomenon is the result of a balance between cell uptake of salt and water at the luminal membrane and exit at the basolateral membrane. Different properties regarding volume regulatory increase and decrease have been found (Eriksson & Spring 1982 and Larson & Spring 1983). The present study links fluid transport and volume regulatory increase of the cell. First we concluded from histological techniques that carbonic anhydrase is present in the cell membrane or in the vicinity of the epithelial cells. Then we measured a decreased net fluid transport in the presence of increasing concentrations of the carbonic anhydrase inhibitor acetazolamide. We showed that the volume regulatory increase is substantially slowed down and that the steady-state volume of the cells changed when carbonic anhydrase was inhibited. Our conclusion is that the rate of CO2 hydration was a limiting step, at carbonic anhydrase inhibition, in both the net transfer of salt and water and also in the ability of the cells to efficiently regulate their volume.