Carbonic anhydrase II (gene name CA2), is one of fourteen forms of humanαcarbonic anhydrases. Carbonic anhydrase catalyzes reversible hydration of carbon dioxide. Defects in this enzyme are associated with osteopetrosis and renal tubular acidosis.

Carbonic anhydrase II is expressed at high levels in osteoclasts during bone resorption. Laitala and Vaananen (1994) demonstrated in 2 in vitro culture systems that antisense RNA and DNA blocked expression of CA II and led to decreased bone resorption. In the choroid plexus, carbonic anhydrase II supports the transport of bicarbonate ions, sodium ions, and water from the blood to the cerebrospinal fluid.