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).

SCHWARZBAUM PJ, WIESER W, COSSINS AR

PHYSIOLOGICAL AND BIOCHEMICAL ZOOLOGY

UNIV CHICAGO PRESS

Año: 1992 p. 17 - 34

1522-2152

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 thermal stability due to acclimation temperature were shown by the τ-glutamyltransferase of both species. The present findings in conjunction with the results of a previous investigation lead to the conclusion that two coexisting species of fish, belonging to different families, use different strategies of membrane adaptation to environmental temperature. The cyprinid, R. rutilus, responded to low-temperature acclimation predominantly by altering the properties of the (Na⁺ + K⁺)ATPase (ouabain-binding sites, specific activity, thermal stability), whereas the salmonid, S. alpinus, responded by altering bulk fluidity and residual K⁺ efflux. These species-specific differences are discussed with regard to the consequences of possible imbalances of ionic flux created by different temperature coefficients of active transport and dissipative permeation of ions.