Osmotic and Ionic Regulation in Mammals

Renal responses to salinity change in snakes with and without salt glands

“…Further, we demonstrate an apparent apical or subapical localization of putative AQP3 in the cells comprising the late distal tubule epithelium in L. semifasciata (Fig.8A). This apical localization of putative AQP3 in the distal tubule of sea snakes was surprising but is also reminiscent of the localization of AQP3 to the apical membranes of chloride cells in the gills of silver eels (Lignot et al, 2002) and the localization of AQP2 in the apical membranes and subapical vesicles of the collecting duct in mammals (Kinne and Zeidel, 2009). Interestingly, peptide preabsorption of Hc-3 completely abolishes all staining in the kidney of all three species examined (Fig.10), suggesting that the immunoreactivity was a specific result of the interaction of antibody Hc-3 with its antigen.…”

“…By contrast, the basal extrusion of Na + is facilitated by Na + /K + -ATPase (NKA) in all segments of the mammalian kidney (Kinne and Zeidel, 2009). Although early studies of renal function in snakes provide indirect evidence that some of the same ion transporters may regulate NaCl balance in reptiles as well (Beyenbach and Dantzler, 1978;Dantzler et al, 1991), to our knowledge, no studies have directly examined the distribution and/or abundance of these ion transporters in the kidneys of any reptile species.…”

“…In many vertebrates, this process is stimulated primarily through the action of aquaporin (AQP) 1, in the proximal tubules, and AQP2, -3 and -4 in the distal tubules, connecting segments and collecting ducts Reptilian renal responses to salinity (Borgnia et al, 1999). Both AQP2 and AQP3 are known to be hormonally regulated (via vasopressin) in mammals (Kinne and Zeidel, 2009;Terris et al, 1996), and a similar mechanism of regulation has been proposed for avian AQP2 (Lau et al, 2009) and amphibian AQP2 . Upon stimulation by vasopressin [or arginine vasotocin (AVT) in birds and amphibians], AQP2 is mobilized from the cytoplasmic vesicles, where it is stored, to the apical membrane of the collecting duct cells, facilitating luminal passage of water into the cell (Nielsen et al, 1995).…”

“…Upon stimulation by vasopressin [or arginine vasotocin (AVT) in birds and amphibians], AQP2 is mobilized from the cytoplasmic vesicles, where it is stored, to the apical membrane of the collecting duct cells, facilitating luminal passage of water into the cell (Nielsen et al, 1995). Water then exits the cell via the basolaterally located AQP3 (Kinne and Zeidel, 2009;Sugiura et al, 2008). Although renal expression of AQP3 is restricted to the basolateral membranes of collecting duct cells in mammals and birds, its distribution among amphibians appears to extend into the distal tubules (Akabane et al, 2007;Mochida et al, 2008) and among fishes the localization of AQP3 remains equivocal .…”