CO2Excretion Across Isolated Perfused Crab Gills: Facilitation by Carbonic Anhydrase

Crab gill carbonic anhydrase is shown to facilitate the excretion of carbondioxide across isolated perfused gills. A technique for perfusing crab gills and assessing the metabolic viability of perfused gills is also described in detail. The technique is used to follow the disappearance of 14C label as HCO3− and CO2 from internal perfusate passing through the gill. The excretion of the label increases with the flow rate of the external perfusate across the outside of the gills. The addition of carbonic an hydrase to the internal perfusate results in a two- to fourfold increase in the excretion of label while Diamox (acetazolamide) treatment decreases the excretion of label by half. It is also suggested that carbonic anhydrase, present in muscle tissues of crabs, minimizes the disequilibrium of the hemolymph CO2 system as metabolically produced CO2 leaves the tissues and enters the hemolymph. Parallels are drawn between the presence of carbonic anhydrase in the crab gill system and the presence of this enzyme in the respiratory organs of both aquatic and terrestrial animals.