Evidence for the presence of carbonic anhydrase in the plasma membrane of rat hepatocytes.

The cellular distribution of carbonic anhydrase is a key characteristic for the role of the enzyme in cell function. In several epithelia involved in bicarbonate transport this enzyme is located in the plasma membrane. Because bicarbonate secretion is an important mechanism in bile formation by the liver, we investigated the presence of carbonic anhydrase activity in isolated plasma membranes from rat hepatocytes. Carbonic anhydrase activity was enriched 1.79-fold in plasma membrane preparations. This activity was inhibited by acetazolamide and activated by Triton X-100, but was insensitive to Cl- or CNO-. It is highly unlikely that the low contamination of cytoplasm and intracellular membranes could account for the presence of carbonic anhydrase activity in plasma membrane preparations. Moreover, the results from resuspension/washing of plasma membrane fractions in ionic media suggest an absence of soluble carbonic anhydrase adsorption upon plasma membrane. Accordingly, the present findings provide strong evidence for the presence of carbonic anhydrase in the plasma membrane of rat hepatocytes.