Crustaceans are extremely diverse and widely distributed. The survival and success of this group is the result of the differential selection of physiological mechanisms that provide a stable internal osmotic and ionic environment that protects the cells and tissues against the salinity fluctuations. This osmotic homesostasis appears to have allowed the conquest of the most variable environments, from the fresh water and sea water to dry land, including coastal waters and estuaries, environments of variable salinity. Among the physiological adaptations that have allowed the colonization of these hostile environments are reduction in body permeability and efficient salt absorption and secretion by the gill epithelium responsible for active ion transport based on the Na+/K+- and V-ATPase and the Na+/K+/2Cl- cotransporter. Here, we will evaluate the biochemical and molecular underpinnings of osmorregulatory physiology in Uca, inter-tidal fidder crabs, widely distributed among different osmotic niches along the Atlantic coast of Brazil. We will compare the expression of the ± and B subunits of the gill Na+/K+- and V-ATPase, using quantitative real time RT-PCR mRNA expression, and their enzyme activities. In addition, we will also investigate the participation of the Na+/K+/2Cl- symporter in these processes, using real time RT-PCR mRNA expression. These findings will contribute to elucidate the molecular mechanisms underlying the biochemical and physiological adaptations that sustain osmorregulatory ability, and we allow us to evaluate patterns that might support the wide distribution of these crabs in their various osmotic niches.
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