Branchial carbonic anhydrase is present in the dogfish, Squalus acanthias

The distribution of branchial carbonic anhydrase (CA) in the shark, Squalus acanthias, was studied using in situ measurements of pH disequilibrium sta tes in post-branchial saline, and immunological techniques, immunofluoresce nce microscopy and Western analysis, employing rabbit polyclonal antibodies against rat pulmonary membrane associated CA IV and chick retinal cytosoli c CA II. In the in situ saline perfused gill preparation, the CA inhibitor acetazolamide produced a pH disequilibium (0.063 +/- 0.022 pH units) while control and bovine carbonic anhydrase perfusions did not (0.012 +/- 0.017 a nd 0.023 +/- 0.018 pH units, respectively). These results indicate that the HCO3- dehydration reaction is accelerate by endogenous extracellular CA. W estern analysis of saline perfused gill membrane preparations revealed an i mmunoreactive 48 kDa band with the CA IV probe. In crude gill homogenates, a 33 kDa and 31 kDa pair of bands is identified by the CA II probe. The pat tern of immunolabeling for CA II in the gill epithelium was either diffuse or punctate within both lamellar and filament epithelial cells while eyrthr ocytes and pillar cells displayed a diffuse staining pattern.