Sodium, net acid and ammonia fluxes in freshwater-adapted European flounder (Platichthys flesus L.). Pharmacological inhibition and effects on gill ventilation volume

Net branchial sodium uptake, and net acid and ammonia excretion, together w ith gill ventilation volumes were measured in euryhaline European flounder Platichthys flesus, adapted to freshwater. External amiloride or acetazolam ide (0.1 mmol l(-1)) caused significant reductions (P < 0.05) in sodium upt ake and net acid excretion, while 0.05 mmol l(-1) thiocyanate had no effect on any of the fluxes measured. Ethoxzolamide (0.1 mmol l(-1)) however, cau sed significant reductions in all fluxes measured and also caused a 32% red uction in the volume of water exhaled by the gills. In this study, it appea rs that sodium uptake and net acid excretion are indirectly linked, probabl y by a proton pump arrangement which is thought to be a mechanism for sodiu m uptake in trout gills.