EFFECTS OF COLD-EXPOSURE AND HIBERNATION ON VENAL NA,K-ATPASE OF THE JERBOA JACULUS ORIENTALIS

Changes in activity and abundance of renal Na,K-ATPase were evaluated during cold exposure and hibernation of the jerboa Jaculus orientalis by measuring the hydrolytic activity, the number of units and the tran sport activity of Na,K-ATPase in isolated nephron segments. As compare d to controls, jerboas exposed to cold (6 degrees C) for 4-5 weeks dis played mild diuresis, decreased urinary osmolality and increased kaliu resis. In cold-exposed jerboas, Na,K-ATPase hydrolytic activity was re duced in the medullary thick ascending limb and enhanced in the cortic al and outer medullary collecting duct, whereas it was not altered in other nephron segments. The number of Na,K-ATPase units and the activi ty of Na,K-pump, determined by [H-3]-ouabain binding and by ouabain-se nsitive rubidium uptake respectively, changed in parallel with the hyd rolytic activity in the medullary thick ascending limb and cortical co llecting duct. The maximal rate of activity (V-max) of Na,K-ATPase was not modified further during hibernation. Thus, cold exposure, but not the onset of hibernation, induces segment-specific changes in the abu ndance and activity of Na,K-ATPase units which are likely to be relate d to the entry into hibernation, but not to the maintenance of some re nal functions during deep hibernation.