AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 5 966-R971, Copyright © 1987 by American Physiological Society
Membrane-associated carbonic anhydrase in gills of the blue crab, Callinectes sapidus
R. P. Henry
The presence of the enzyme carbonic anhydrase (CA) on the basal membrane of
the branchial endothelial cells in the blue crab and its physiological
significance were studied in vivo using a membrane-impermeant CA inhibitor,
quaternary ammonium sulfanilamide (QAS). Injection of QAS into the
hemolymph of Callinectes sapidus resulted in the rapid development of a
respiratory acidosis; PCO2 rose almost 2 Torr, pH was lowered by
approximately 0.25 units, and total CO2 rose by 2 mM. These results support
the hypothesis that membrane-associated CA exposed to hemolymph is present
in the crustacean gill and that it is physiologically significant in
mobilizing hemolymph HCO-3 to CO2 to facilitate CO2 excretion across the
gill. The recovery from this acidosis coincides with the clearance of the
inhibitor from the hemolymph. Hemolymph osmotic and ionic parameters were
unaffected by QAS, reconfirming the role of branchial cytoplasmic CA in ion
regulation and also providing a convenient bioassay for determining CA
inhibitor permeability in the intact organism.
