title: Intestinal Na+, K+, 2Cl- cotransporter 2 plays a crucial role in hyperosmotic transitions of a euryhaline teleost.
abstract: Euryhaline fishes, such as the red drum (Sciaenops ocellatus), must quickly transition between hyperosmotic and hypoosmotic physiological strategies. When freshwater individuals transition to seawater they are exposed to increased diffusive water loss and ion gain. To maintain osmoregulatory balance these animals must drink and absorb seawater through the intestine, followed by ion excretion at the gills. The ability of fishes to transition between strategies can limit the magnitude of osmotic shock that can be tolerated. Here, we demonstrate that red drum can tolerate direct transfer from freshwater to full-strength seawater with marginal impacts on osmotic balance, as indicated by plasma and muscle ion concentration, as well as muscle water. Seawater transition is concurrent with a significant increase in intestinal fluid volume. Typical patterns of osmoregulatory plasticity were observed in the gill with increased expression of nkcc1 and cftr Expression changes in the anterior intestine were observed after 24 h for nkcc2 with smaller and later responses observed for slc26a3, slc26a6, and nbc Immunofluorescence staining demonstrated similar patterns of NKCC localization in freshwater and seawater intestines; however, reduced basolateral staining of V-type ATPase was observed in seawater. Electrophysiological preparations demonstrated that seawater fish had increased absorptive current in the anterior intestine, which was significantly reduced in the presence of 10 μmol/L bumetanide. Overall, these results suggest that nkcc2 plays a crucial role during hyperosmotic transitions, and may be a more important complement to the well-known bicarbonate secretion pathway than generally considered.
authors.affiliation: University of Texas at Austin Marine Science Institute, Austin, Texas a.esbaugh@austin.utexas.edu.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Esbaugh
authors.affiliation: University of Texas at Austin Marine Science Institute, Austin, Texas.
authors.forename: Brett
authors.initials: B
authors.lastname: Cutler
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002034:Bumetanide / Q000008:administration & dosage / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water; D015870:Gene Expression / Q000235:genetics; D005880:Gills / Q000378:metabolism / Q000502:physiology*; D007408:Intestinal Absorption / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000502:physiology*; D017136:Ion Transport / Q000502:physiology; D064587:Osmoregulation / Q000235:genetics / Q000502:physiology*; D054712:Salinity; D012623:Seawater / Q000009:adverse effects*; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D064466:Solute Carrier Family 12, Member 1 / Q000187:drug effects / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2 / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism
chemical_list: D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D064506:Solute Carrier Family 12, Member 2; D002034:Bumetanide; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D025262:Vacuolar Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Euryhaline; NKCC; V‐type ATPase; ion regulation; red drum; salinity transfer; water absorption