Tissue-specific differences and temperature-dependent changes in Na, K-ATPase of the roach (Rutilus rutilus)

Na,K-ATPase activity is vital for virtually all cells of the animal body and the major consumer of cellular energy. However, Na,K-ATPase activity, the number of Na+ pump units, the catalytic rate of the pump, and their responses to thermal acclimation in different tissues of the same fish species have been seldom measured. Therefore, roach (Rutilus rutilus), eurythermal freshwater fish, was acclimated at 4 degrees C (cold-acclimated, CA) and 18 degrees C (warm-acclimated, WA), and the Na+ pump density and the temperature-dependence of Na,K-ATPase activity were determined in the heart, gills, kidney and brain. There were prominent tissues specific differences in Na,K-ATPase activity. The activity was highest in the brain (100%), whereas the activity of renal, branchial and cardiac enzymes was 55%, 9%, and 4% of the brain activity in the WA roach at 25 degrees C. The corresponding values for brain, kidney, gills and heart of the CA fish at 25 degrees C were 100%, 56%, 5% and 4%, respectively. The number of Na,K-ATPase alpha-subunits, determined by [H-3]ouabain binding, strongly correlated with the Na,K-ATPase activity at R-2 values of 0.99 and 0.85 for WA and CA fish, respectively. Acclimation to cold, increased the number of Na,K-ATPase alpha-subunits in the heart, kidney and brain (P < 0.05), but this did not appear as an increase in Na,K-ATPase activity. In the gills, Na,K-ATPase alpha-subunits did not change in cold -acclimation, but Na,K-ATPase activity was depressed. Although tissue-specific differences in Na,K-ATPase activity are largely determined by the density of alpha-subunits, differences in Na,K-ATPase activity within the same tissue due to temperature acclimation involve also other factors in addition to the number of Na+ pump units.