Differential expression and induction of two carbonic anhydrase isoforms in the gills of the euryhaline green crab, Carcinus maenas, in response to low salinity

The cytoplasmic isoform of carbonic anhydrase increases 100-fold in abundance in green crab gills when acclimated to low salinity.

• The membrane-associated isoform of carbonic anhydrase shows a 3-fold increase initially in low salinity before stabilizing.
• A 20-fold increase in carbonic anhydrase protein-specific activity is linked to the rapid rise in cytoplasmic isoform mRNA during low salinity acclimation.
• Maximal levels of cytoplasmic isoform mRNA expression occur by 24 hours, aligning with the stabilization of hemolymph osmotic and ionic levels.
• Changes in the expression of the membrane-associated isoform are associated with alterations in the population of branchial chloride cells.
• Expressions of other genes, such as the alpha-subunit of the Na(+)/K(+)-ATPase, show smaller changes compared to the cytoplasmic isoform, but with a similar timing.

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