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

Abstract

Net branchial sodium uptake, and net acid and ammonia excretion, together with gill ventilation volumes were measured in euryhaline European¯ounder Platichthys¯esus, adapted to freshwater. External amiloride or acetazolamide (0.1 mmol l -1 ) caused signi®cant reductions (P < 0.05) in sodium uptake and net acid excretion, while 0.05 mmol l -1 thiocyanate had no effect on any of the¯uxes measured. Ethoxzolamide (0.1 mmol l -1 ) however, caused signi®cant reductions in all¯uxes measured and also caused a 32% reduction in the volume of water exhaled by the gills. In this study, it appears that sodium uptake and net acid excretion are indirectly linked, probably by a proton pump arrangement which is thought to be a mechanism for sodium uptake in trout gills.

Visualization in zebrafish larvae of Na+uptake in mitochondria-rich cells whose differentiation is dependent onfoxi3a

“…In this model, energy consumptive excretion of H ϩ by H ϩ -ATPase creates an electrical gradient that provides the driving force to draw in Na ϩ through ENaC from the diluted environment. This model has been supported by several pharmacological studies with selective inhibitors of ENaC and H ϩ -ATPase (9,11,31,32,45,46). Currently, identification of an ENaC homologue from fish has not been successful.…”