Mecanismos de regulação de Na+ nas brânquias de peixes da Amazônia: modulação por fatores ambientais e ajustes espécie-específicos

Abstract

The mechanisms of Na+ transport in gills of Amazonian fish species remains poorly understood, particularly regarding to the physiological adjustments involved in adaptation to the singular environmental conditions of Amazon waters. The aim of the present study was analyze the physiological mechanisms involved in Na+ transport in gills of different Amazonian fish species, at both natural and laboratory conditions. Therefore, we evaluated the influence of water physical and chemical conditions on Na+ unidirectional fluxes and Na+ uptake kinetic properties of fishes, as well as on Na+/K+-ATPase and H+-ATPase activity, looking for intraespecific and interespecific adjustments in Na+ transport according to environmental conditions. The responses in branchial Na+ transport were strongly related to H+-ATPase activity, suggesting that this enzyme plays a importante role in the maintenance of the ionic and acid-base balance in the studied fish species during the process of acclimatization and acclimation to acidic conditions ion-poor conditions. However, others Na+ transporters seems to be involved in branchial transport of Na+, particularly in Hyphessobrycon copelandi during acute exposure to higher temperatures. There was also seen that differences in controlling gill permeability modulate the tolerance of some cichlid fish species, as Pterophyllum scalare and Symphysodon discus, to ionoregulatory disturbances from the exposure to acidic water and ion-poor conditions. Moreover, intraspecific and interspecific variation in the response of H+-ATPase activity, and in a lower extent to the Na+/K+-ATPase activity, were associated with adaptive adjustments of fish to the natural environmental conditions founded in streams of the Rio Negro basin.