Crustaceans hyper-osmoregulate in dilute media or freshwater using mechanisms of isosmotic intracellular and anisosmotic extracellular regulation. The latter involves the active transport of salt into the hemolymph, maintaining an osmotic concentration well above that of the surrounding medium. This salt uptake mechanism is based on the activity of an ion transporting protein, the Na+/K+-ATPase, located in the basal membranes of the ionocytes that constitute the epithelia of the gills and antennal gland renal tubules, and on other transport proteins. The osmotic movement of water is another important component of osmoregulation, particularly isosmotic intracellular regulation. Water movement down its osmotic gradient takes place mainly through transmembrane water-channel proteins known as aquaporins. In this study, we will investigate osmoregulatory processes at the systemic level, accompanying hemolymph osmolality and chloride concentration, and at the molecular level, by monitoring the quantitative expression of the Na+/K+-ATPase and aquaporin genes in two hololimnetic freshwater crustaceans: a palaemonid shrimp Macrobrachium brasiliense, and an anomuran Aegla franca, subjected to different osmotic gradients. Our findings should allow a better understanding of osmoregulatory mechanisms in the Decapoda, integrating information gathered at the systemic level with associated molecular responses, in two phylogenetically distant taxa.
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