EFFECTS OF CARBONIC-ANHYDRASE INHIBITION ON THE ACID-BASE STATUS IN LAMPREY AND TROUT

Inhibition of red cell carbonic anhydrase (CA) activity resulted in th e rapid development of a respiratory acidosis (0.25 pH depression with in 15 min post-injection) in the blood of trout. In the lamprey, howev er, the onset of the respiratory acidosis was delayed and its magnitud e was less (0.18 pH depression al 6 h post-injection). Erythrocyte pH of both species decreased by about 0.12 units by 1 h after CA inhibiti on. These data, combined with the lack of rapid anion (Cl-/HCO3(-)) ex change in the red cells of agnathans but not in other lower vertebrate s, support the hypotheses that (1) the majority of total CO2 in lampre y is transported within the erythrocyte, and (2) the limiting step in the evolution of a functioning Jacobs-Stewart cycle, and thus the evol ution of the common mechanism of systemic CO2 transport in vertebrate blood, was the incorporation of the band-3 anion exchange protein into the membrane of the red cell.