Carbonic Anhydrase Activity and Ion Regulation in Three Species of Osmoregulating Bivalve Molluscs

Abstract

Carbonic anhydrase (CA) activity in gill and mantle tissue of Rangia cuneata, Ligumia subrostrata, and Corbicula fluminea increases when the animals are subjected to osmotic stress; there is no such increase in either adductor muscle or visceral mass. A 12-h exposure to the CA inhibitor acetazolamide impairs the animals' ability to maintain blood Na⁺ and Cl⁻ concentrations at normal levels above ambient, with blood Cl⁻ being lowered more than Na⁺. In L. subrostrata, Na⁺ influx is lowered, and Cl⁻ efflux is raised by acetazolamide. We conclude that CA is important in the ion regulatory process, probably in generating H⁺ and HCO₃⁻ from CO₂, which act as counterions in Na⁺ and Cl⁻ uptake, respectively. The flux data indicate that the role of the enzyme in the specific mechanisms of individual ion transport needs further investigation.