AJP - Gastrointestinal and Liver Physiology, Vol 247, Issue 3 213-G219, Copyright © 1984 by American Physiological Society
Carbonic anhydrase activity and aminopyrine uptake in isolated gastric mucosal cells
A. Wollin
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/10(6) 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. The present data from isolated
cells suggest that cellular carbonic anhydrase in the oxyntic cell 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.
