Fig. 5. Hypothetical model showing the various proton-translocating mechanisms
identified so far in swimbladder gas gland cells of the European eel. Acidic
metabolites (lactic acid and CO2) are produced in the glycolytic
pathway and in the pentose phosphate shunt. This acid is secreted at the
basolateral membranes to reduce the effective gas-transport capacity of the
blood via the Root effect and the salting out effect (see
Pelster, 1997;
Pelster and Randall, 1998).
The decrease in gas-transport capacity induces an increase in gas partial
pressures in the blood, which provides the necessary partial pressure gradient
towards the swimbladder lumen so that gases can enter the swimbladder by
diffusion. The mechanisms of lactate transport have not yet been characterized
in detail. CA, membrane-bound carbonic anhydrase.
