Summary
Freshwater eel gills are notorious for their limited ability to pump chloride. As a result there is a considerable discrepancy between the Na+ and Cl− plasma levels, and plasma HCO3 − and blood pH are relatively high in this species.
When eels are kept in tanks aerated with pure oxygen, significant alterations in blood acid-base balance, an increase in plasma pCO2 and a decrease in blood pH, are observed. In fish studied after 3 weeks hyperoxia, the decrease in blood pH is compensated by an increase in plasma HCO3 −. Such fish exhibit a Cl− influx 5 times higher than that observed in normoxic fish. This Cl− influx is readily inhibited by addition of SCN− to the external medium.
An anion-stimulated ATPase activated by HCO3 − and by Cl− and inhibited by SCN− was recently described in membrane fractions of the gills ofCarassius auratus, a fish noted for its high Cl− pumping rate. This enzyme is also found in the gills of the eel. While the maximal rates of enzyme activation by HCO3 − and by Cl− are similar inCarassius andAnguilla, the affinity of the enzyme for Cl− is 25 times higher inCarassius. In the microsomal fraction of the hyperoxic eel gills, the maximal anionstimulated ATPase activity remains unchanged but HCO3 − affinity decreases by 50%, while Cl− affinity increases 5 times. Thus some characteristics of this ATPase seem to be closely related to the Cl− pump activity exhibited by the gill in fresh water.
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Bornancin, M., De Renzis, G. & Maetz, J. Branchial Cl transport, anion-stimulated ATPase and acid-base balance inAnguilla anguilla adapted to freshwater: Effects of hyperoxia. J Comp Physiol B 117, 313–322 (1977). https://doi.org/10.1007/BF00691557
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DOI: https://doi.org/10.1007/BF00691557