Species-Specific Responses of Membranes and the Na++ K+Pump to Temperature Change in the Kidney of Two Species of Freshwater Fish, Roach (Rutilus rutilus) and Arctic Char (Salvelinus alpinus)

Abstract

A protocol has been developed for the separation of brush-border membrane (BBM) and basolateral membrane (BLM) fractions from the kidneys of the roach (Rutilus rutilus) and the Arctic char (Salvelinus alpinus), based on differential precipitation and differential centrifugation. Steady state polarization fluorescence was used to measure membrane fluidity in BBM and BLM from the kidneys of cold- and warm-acclimated fish. The homeoviscous response (%HR) in the BLM of cold-acclimated S. alpinus was about four fold higher (78.2%) than in the BLM of cold-acclimated R. rutilus. No %HR was shown by the BBM of R. rutilus, but a fairly strong one (54.3%) by the BBM of S. alpinus. Acclimation temperature had no effect on thermal stabilit, of the (Na⁺ + K⁺)-ATPase from kidney microsomes of S. alpinus, but the preincubation temperature that resulted in 50% inactivation $(LT_{50})$ of the same enzyme was significantly (> 2° C) lower in coldthan in warm-acclimated R. rutilus. No changes or only slight changes of ther...