Effects of variations in food intake on renal sodium pump activity and its gene expression in Psammomys kidney

P. Scherzer, I. Nachliel, E. Ziv, H. Bar-On, M. M. Popovtzer
2000 AJP - Renal Physiology  
Scherzer, P., I. Nachliel, E. Ziv, H. Bar-On, and M. M. Popovtzer. Effects of variations in food intake on renal sodium pump activity and its gene expression in Psammomys kidney. Am J Physiol Renal Physiol 279: F1124-F1131, 2000.-Psammomys obesus lives in an arid environment and feeds on saltbush. When animals are fed a laboratory diet, urine osmolarity drops. To explore the mechanism(s) of water conservation, we measured renal function, kidney solute content, Na-K-ATPase activity, and mRNA in
more » ... everal groups: group I (saltbush diet, 18 g/day, 4.2 g protein); group II (laboratory diet, 10 g/day, 1.8 g protein); and group III, the same as group I, and group IV, the same as group II, both plus a 1-day fast. Urine osmolarity was 2,223 Ϯ 160, 941 Ϯ 144, 1,122 Ϯ 169 and 648 Ϯ 70.9 mosM in groups I, II, III, and IV, respectively. Tissue osmolarities in cortex, outer medulla, and inner medulla, respectively, were 349 Ϯ 14, 644 Ϯ 63, and 1,152 Ϯ 34 osM/mg tissue in group I; 317 Ϯ 24, 493 Ϯ 17, and 766 Ϯ 60 osM/mg tissue in group II; 335 Ϯ 6, 582 Ϯ 15, 707 Ϯ 35 osM/mg tissue in group III; and 314 Ϯ 18, 490 Ϯ 22, and 597 Ϯ 29 osM/mg tissue in group IV. There were no differences in Na-K-ATPase activity and mRNA in cortex and in medulla between groups I and II, whereas in group III Na-K-ATPase activity and mRNA increased in cortex and outer medulla. These results suggest a key role for urea in corticomedullary osmotic gradient of Psammomys. The absence of differences in Na-K-ATPase activity and mRNA between groups I and II despite differences in tissue sodium concentrations is consistent with Na-K-ATPase-independent Na absorption. Increased Na-K-ATPase activity and mRNA in fasting suggest transition to Na-K-ATPase-dependent Na transport. Address for reprint requests and other correspondence: P. Scherzer, Nephrology and Hypertension Services,
doi:10.1152/ajprenal.2000.279.6.f1124 pmid:11097632 fatcat:g4nx5vauyzejvkcyjwqyzg5m2a