Comparative immunolocalization of Na+/K+‐ATPase and Na+/K+/2Cl− cotransporter in the kidneys of freshwater and marine snakes

Abstract

In contrast with the marine sea snakes, watersnakes in the genus Nerodia are not known to have functional salt glands. Despite this physiological difference, at least two species of watersnake are known to inhabit marine environments; the remaining members of this genus occupy freshwater habitats. The mechanism by which marine watersnakes regulate ion balance without functional salt glands is unknown. In this study, we compared the cellular anatomy of kidneys from two species of watersnake, Nerodia fasciata (freshwater) and N. clarkii (marine), and one species of sea snake, Laticauda semifasciata (marine). Specifically, we examined the localization of Na+/K+‐ATPase (NKA) and Na+/K+/2Cl− cotransporter (NKCC), two proteins that are known to regulate membrane potential and drive salt secretion in all vertebrate secretory cells examined to date. Using histology and immunohistochemistry, we localized NKA and NKCC to the basolateral membranes of the distal tubules in all three species of snake. These results are consistent with the localization of these proteins in other secretory tissues such as the gills of teleost fishes and the salt glands of marine elasmobranchs, birds, and reptiles, and suggest a potential role for ion regulation at the level of the kidney. This research was funded by the National Geographic Society (8058‐06 to HBL) and the National Science Foundation (IOB‐0519579 to DHE).