Urine pH and carbonic anhydrase activity in the marine dogfish.

EVERAL S years ago it was reported by Smith (I) that the acidity of the urine in both the marine dogfish and sculpin is fixed at about PH 5.7 and cannot be changed by the intravenous administration of sodium bicarbonate, alkaline phosphate or phlorizin. The suggestion was then made that this fixation of urine PH might be related to the fact that in the marine fishes the urine contains large quantities of magnesium which precipitates as Mg(OH)2 or MgHP0403H20 (2) if the PH exceeds 6.0. The mechanism of acidification was, by a process of exclusion, related to exchange of Hf for cations (3). Support for the H+-exchange mechanism was subsequently adduced by others (4-6) in mammals, using either sulfanilamide or the sulfonamide derivative Diamox (6063, 2acetylamine I, 3,4 thiadiazole 5 sul fonamide) to inhibit the carbonic anhydrase involved in the H+-exchange mechanism. The present study was designed to determine whether a carbonic anhydrase-dependent system susceptible to inhibition by Diamox, exists in the kidney of the marine dogfish, and to explore further the mechanism by which a constant urine PH is maintained despite considerable change in plasma PH. During the course of these studies, using a variety of marine and fresh-water fish, it was demonstrated that: a) a carbonic anhydrase-dependent system is not involved in the acidification of the urine in the dogfish (Squalus