Effects of carbonic anhydrase inhibition on the acid base status in lamprey and trout

Abstract

Inhibition of red cell carbonic anhydrase (CA) activity resulted in the rapid development of a respiratory acidosis (0.25 pH depression within 15 min post-injection) in the blood of trout. In the lamprey, however, the onset of the respiratory acidosis was delayed and its magnitude was less (0.18 pH depression at 6 h post-injection). Erythrocyte pH of both species decreased by about 0.12 units by 1 h after CA inhibition. These data, combined with the lack of rapid anion ( Cl − HCO − 3 ) exchange in the red cells of agnathans but not in other lower vertebrates, support the hypotheses that (1) the majority of total CO 2 in lamprey is transported within the erythrocyte, and (2) the limiting step in the evolution of a functioning Jacobs-Stewart cycle, and thus the evolution of the common mechanism of systemic CO 2 transport in vertebrate blood, was the incorporation of the band-3 anion exchange protein into the membrane of the red cell.