Functional classification of mitochondrion-rich cells in euryhaline Mozambique tilapia (Oreochromis mossambicus) embryos, by means of triple immunofluorescence staining for Na+/K+-ATPase, Na+/K+/2Cl- cotransporter and CFTR anion channel.
Mozambique tilapia Oreochromis mossambicus embryos were transferred from freshwater to seawater and vice versa, and short-term changes in the localization of three major ion transport proteins, Na+/K+-ATPase, Na+/K+/2Cl- cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR) were examined within mitochondrion-rich cells (MRCs) in the embryonic yolk-sac membrane. Triple-color immunofluorescence staining allowed us to classify MRCs into four types: type I, showing only basolateral Na+/K+-ATPase staining; type II, basolateral Na+/K+-ATPase and apical NKCC; type III, basolateral Na+/K+-ATPase and basolateral NKCC; type IV, basolateral Na+/K+-ATPase, basolateral NKCC and apical CFTR. In freshwater, type-I, type-II and type-III cells were observed. Following transfer from freshwater to seawater, type-IV cells appeared at 12 h and showed a remarkable increase in number between 24 h and 48 h, whereas type-III cells disappeared. When transferred from seawater back to freshwater, type-IV cells decreased and disappeared at 48 h, type-III cells increased, and type-II cells, which were not found in seawater, appeared at 12 h and increased in number thereafter. Type-I cells existed consistently irrespective of salinity changes. These results suggest that type I is an immature MRC, type II is a freshwater-type ion absorptive cell, type III is a dormant type-IV cell and/or an ion absorptive cell (with a different mechanism from type II), and type IV is a seawater-type ion secretory cell. The intracellular localization of the three ion transport proteins in type-IV cells is completely consistent with a widely accepted model for ion secretion by MRCs. A new model for ion absorption is proposed based on type-II cells possessing apical NKCC.
Hiroi
Junya
J
Department of Anatomy, St Marianna University School of Medicine, Miyamae-ku, Kawasaki 216-8511, Japan. j-hiroi@marianna-u.ac.jp
McCormick
Stephen D
SD
Ohtani-Kaneko
Ritsuko
R
Kaneko
Toyoji
T
D000222:Adaptation, Physiological; D000818:Animals; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000502:physiology*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology; D005455:Fluorescent Antibody Technique; D005618:Fresh Water; D008928:Mitochondria / Q000502:physiology*; D012623:Seawater; D028021:Sodium-Potassium-Chloride Symporters / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D017210:Tilapia / Q000196:embryology* / Q000502:physiology; D015017:Yolk Sac / Q000378:metabolism
D028021:Sodium-Potassium-Chloride Symporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000254:Sodium-Potassium-Exchanging ATPase