Urine pH and Carbonic Anhydrase Activity in the Marine Dogfish

Abstract

This study was undertaken to investigate the mechanisms responsible for a fixed urine pH in the marine dogfish (Squalus acanthias). Injection of a variety of chemical substances, including enzyme inhibitors, failed to alter the urine pH. It was further demonstrated, in contrast to the freshwater catfish (Ameirus nebulosus) and mammal, that a carbonic anhydrase dependent system, capable of inhibition by Diamox (2-acetylamine-1,3,4-thiadiazole-5-sulfonamide), does not exist in the dogfish kidney. After exclusion of other, extrarenal sites of carbonic anhydrase activity, it is concluded that Diamox inhibits carbonic anhydrase in the red blood cell and the gills. Evidence is presented that carbonic anhydrase plays a role in the branchial excretion of NaHCO3.