title: Dissociation of CO2 hydration and renal acid secretion in the dogfish, Squalus acanthias.
abstract: Maximal rates of renal hydrogen ion secretion and bicarbonate reabsorption in the dogfish were stimulated by intravascular infusion of acidic and basic buffers: bicarbonate, phosphate, phenol red, dimethadione (DMO), imidazole, and piperazine-N,N'-bis(2 ethanesulfonic acid) (PIPES). There was no difference in titratable acid secretion or urinary pH after bicarbonate infusion despite a sevenfold increase in plasma bicarbonate. Bicarbonate reabsorption was increased 12-fold and showed no evidence of reaching a maximum. This was not altered by methazolamide, as expected, since there is no renal carbonic anhydrase in seagoing fish. Imidazole resulted in the greatest augmentation of renal titratable acid secretion (33----390 mueq . h-1 . kg-1) and did not alter urinary pH. Inhibition of organic base secretion by Darstine had no effect on the imidazole-induced maximal rate of acid secretion. This rate was compared with that of hydrogen ion generation calculated from the uncatalyzed reactions of CO2 and H2O or OH-, maximizing PCO2 and OH- gradients and reaction volumes in vivo. These calculated chemical rates could only account for 9-14% of the measured maximal acidification rate. Thus the powerful process that maintains constant acid urine pH is not only independent of carbonic anhydrase but can function well in a low CO2 environment in which the reactions CO2 + H2O or CO2 + OH- do not furnish enough protons for H+ secretion or HCO3- reabsorption. We conclude that following the cellular protolysis of water, processes other than those involving CO2 buffering of OH- permit H+ to engage in the formation of urine.
mesh_terms: D000136:Acid-Base Equilibrium; D000476:Alkanesulfonates; D017738:Alkanesulfonic Acids; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D004284:Dogfish / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008433:Mathematics; D010879:Piperazines; D012754:Sharks / Q000378:metabolism*
chemical_list: D000476:Alkanesulfonates; D017738:Alkanesulfonic Acids; D001639:Bicarbonates; D010879:Piperazines; D002245:Carbon Dioxide; D006859:Hydrogen; C008916:piperazine-N,N'-bis(2-ethanesulfonic acid)