Comparative Analysis of Na-K-ATPase Protein Expression Levels in the Outer Medullary Portion of the Kangaroo Rat and the Sprague Dawley Rat Kidney

Abstract

Certain proteins in the thick ascending limb of the nephron are thought to help create the urine concentration gradient in mammalian kidneys. Kangaroo rats have very concentrated urine because of their dry environment and thus make a useful species for comparison against the normal laboratory rat. Concentrations of NaK-ATPase were measured using Western Blot Analyses. The tissue was dissected to isolate the outer medullary region, which consists predominantly of the thick ascending limb. The membrane fraction of the tissue was blotted with an antibody against the NaK-ATPase alpha subunit and read with an infrared imaging system. The results showed that NaK-ATPase protein levels were over three fold higher in the kangaroo rat relative to the Sprague Dawley rat, supporting the hypothesis that more active sodium reabsorption occurs in the kangaroo rat. The release of inorganic phosphate was also measured to determine ouabain-sensitive NaK-ATPase activity. Total ATPase activity was 905 ± 122 for kangaroo rat and 721 ± 111 for Munich-Wistar rat (Mean ± SE). NaK-ATPase activity was greater in the kangaroo rat (204 ± 65) than in Munich-Wistar rat (79 ± 62).