Salt levels change the activity and production of two carbonic anhydrase enzymes in blue crabs

The cytoplasmic isoform of carbonic anhydrase in blue crab gills shows a 100-fold increase in mRNA expression when exposed to low salinity (15 p.p.t.).

• Two isoforms of carbonic anhydrase, CasCAg and CasCAc, were identified in blue crab gills.
• The membrane-associated isoform, CasCAg, has higher mRNA levels in crabs acclimated to high salinity (35 p.p.t.).
• After exposure to low salinity, the cytoplasmic isoform, CasCAc, undergoes significant up-regulation, suggesting a role in overcoming diffusion limitations.
• The expression of CasCAc corresponds with increased protein-specific carbonic anhydrase activity and protein concentration.
• No changes in carbonic anhydrase expression or activity were observed in the anterior gills.
• The expression pattern of the Na+/K+-ATPase alpha-subunit mirrors that of CasCAc, indicating a coordinated response to low salinity.

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