title: Effects of variations in food intake on renal sodium pump activity and its gene expression in Psammomys kidney.
abstract: 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 several 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 +/- 160, 941 +/- 144, 1,122 +/- 169 and 648 +/- 70.9 mosM in groups I, II, III, and IV, respectively. Tissue osmolarities in cortex, outer medulla, and inner medulla, respectively, were 349 +/- 14, 644 +/- 63, and 1,152 +/- 34 microosM/mg tissue in group I; 317 +/- 24, 493 +/- 17, and 766 +/- 60 microosM/mg tissue in group II; 335 +/- 6, 582 +/- 15, 707 +/- 35 microosM/mg tissue in group III; and 314 +/- 18, 490 +/- 22, and 597 +/- 29 microosM/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.
authors.affiliation: Nephrology and Hypertension Services, Hadassah University Hospital, Jerusalem, Israel 91120. popovtzer@Hadassah.org.il
authors.forename: P
authors.initials: P
authors.lastname: Scherzer
authors.forename: I
authors.initials: I
authors.lastname: Nachliel
authors.forename: E
authors.initials: E
authors.lastname: Ziv
authors.forename: H
authors.initials: H
authors.lastname: Bar-On
authors.forename: M M
authors.initials: MM
authors.lastname: Popovtzer
mesh_terms: D000450:Aldosterone / Q000097:blood; D000818:Animals; D015152:Blotting, Northern; D003404:Creatinine / Q000097:blood / Q000652:urine; D004032:Diet; D004231:Diuresis / Q000502:physiology; D004435:Eating / Q000502:physiology*; D005215:Fasting / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics*; D005849:Gerbillinae / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology*; D008861:Microsomes / Q000201:enzymology; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000096:biosynthesis; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D000450:Aldosterone; D003404:Creatinine; D000254:Sodium-Potassium-Exchanging ATPase