Carbonic anhydrase activity and aminopyrine uptake in isolated gastric mucosal cells

Abstract

The role of carbonic anhydrase in the regulation and production of gastric acid was examined. Studies were done on isolated rabbit fundic mucosal cells, in which carbonic anhydrase activity and [14C]aminopyrine uptake were measured. The oxyntic cell-enriched cell fractions had the largest carbonic anhydrase content (4.2 .+-. 0.1 U/106 cells) compared with other mucosal cells. The cellular carbonic anhydrase content of all isolated cell fractions was primarily a soluble enzyme, accounting for 10% of the total mucosal enzyme quantity. The remainder was found in the incubation medium from the mucosal dispersion procedure. The remaining cellular carbonic anhydrase activity in the oxyntic cell fraction was not enhanced by secretagogues. [14C]aminopyrine uptake increased dose dependently in the presence of histamine and dibutyryl cAMP. Acetazolamide (0.2 mM) inhibited the cellular carbonic anhydrase activity (99%) but did not interfere with the cellular uptake of [14C]aminopyrine. Cellular carbonic anhydrase in the oxyntic cell apparently does not appear to be an integral step in the initiation of secretory function of isolated oxyntic cells. The lack of interference by the carbonic anhydrase inhibitor with H+ production does not exclude a role for carbonic anhydrase at high levels of acid secretion as it may occur in vivo, since isolated oxyntic cells probably do not achieve maximal rates of acid secretion and aminopyrine uptake reflects acid gradients and not rate of acid secretion.