Possible role of carbonic anhydrase, V-H+-ATPase, and Cl−/HCO3− exchanger in electrogenic ion transport across the gills of the euryhaline crab Chasmagnathus granulatus

We studied the participation of carbonic anhydrase (CA), V-H+-ATPase, and Cl−/HCO3− exchanger in electrogenic ion absorption through the gills of Chasmagnathus granulatus. CA activity was measured in anterior gills and posterior gills after acclimation to 2‰, 10‰, 30‰ (about seawater), and 45‰ salinity. The highest CA specific activity was detected in the microsomal fraction in anterior gills, and in the cytosolic fraction, in posterior ones. Both fractions were strongly induced by decreasing salinity only in posterior gills. Perfusion of posterior gills from crabs acclimated to either 2‰ or 10‰ with acetazolamide inhibited CA activity almost completely. In posterior gills from crabs acclimated to 2‰ and perfused with 20‰ saline (iso-osmotic for these crabs), acetazolamide reduced transepithelial potential difference (Vte) by 47%, further addition of ouabain enhanced the effect to 88%. Acetazolamide had no effect in the same gills perfused with 30‰ saline (iso-osmotic for seawater acclimated crabs). Bafilomycin A1 and SITS (inhibitors of V-H+-ATPase and Cl−/HCO3−) reduced Vte by 15-16% in gills perfused with normal 20‰ saline, and by 77% and 45%, respectively when they were applied in Na-free 20‰ saline, suggesting the participation of those transporters and cytosolic CA in electrogenic ion absorption.