Ion transport systems in the kidney and urinary bladder of two Antarctic teleosts, Chionodraco hamatus and Trematomus bernacchii

Na+-K+-Cl- cotransport and Na+/K(+)AT-Pase were studied by immunohistochemi stry in the kidney and urinary bladder of Trematomus bernacchii and Chionod raco hamatus. The activity was correlated to the density of mitochondria. T he first segment of the renal proximal tubule was more active than the seco nd one. In T. bernacchii and the temperate marine teleost Pagellus bogarave o, the immunoreactivity for the antibody to cotransporters and to the a-sub unit of the sodium pump was stronger than in the icefish. This difference i ndicates in the kidney of the icefish, a weaker secretory activity, a conse quent lower osmolarity in the lumen and lower water loss, which correlates well with the need for a greater blood volume in the icefish. The epitheliu m of the urinary bladder in T. bernacchii, when intense immunostaining was observed, was composed of columnar cells. In C. hamatus the columnar cells. where the immunostaining was weaker, lined only a portion of the urinary b ladder, the other region being composed of cuboidal cells.