Chloride secretion by the gill epithelium of shrimps and crabs from different osmotic niches: a physiological and molecular investigation of the Na+-K+-2Cl- symporter

Abstract

Owing to their evolutionary history, the subphylum Crustacea unites extant species from widely differing osmotic environments like marine, estuarine and fresh waters, including habitats of varying salinity. Crustaceans compensate physiologically at both the systemic and cellular levels for osmotic and ionic challenges arising in their surrounding aquatic media, providing osmotic and ionic homeostasis of their internal fluids. The gill epithelium constitutes an important interface of compensatory, active ion transport, and the membranes of its constituent ionocytes express ion transporters that drive the transepithelial movement of ions against their gradients. Among these tranporters, the Na+-K+-2Cl- symporter (NKCC) plays a significant role in compensatory salt uptake and secretion, also participating in cell volume regulation by non-epithelial cells. In this investigation, we aim to establish a role for the NKCC in crustaceans from different osmotic niches that exhibit distinct osmoregulatory patterns, particularly as regards Cl- secretion. We will use a clade of caridean shrimps (Palaemon northropi [marine], Macrobrachium acanthurus [diadromous, freshwater], Macrobrachium brasiliense [hololimnetic, freshwater]) and brachyuran crabs (Callinectes danae [marine], Pachygrapsus transversus, Acanthocyclus albatrossis e Halicarcinus planatus [intertidal], Goniopsis cruentata [mangrove] and Dilocarcinus pagei [fresh water]) as models. We will examine the effect of exposure to elevated salinity on hemolymph osmolality and Cl- concentration, and on quantitative protein and gene expression of the NKCC in the gill tissue, employing biochemical and molecular analyses. Owing to the role of the NKCC in both secretion and absorption of Cl-, the precise location of the symporter, whether in the basal or apical membrane of the gill ionocytes, will be identified by immunofluorescence microscopy. Our ultimate goal is to establish whether the two groups, Caridea and Brachyura, share similar Cl- transport mechanisms, and whether the mechanisms encountered in the selected species within each group share similarities. (AU)