Plasma aldosterone/corticosterone and urine electrolyte levels. Plasma aldosterone/corticosterone and urine electrolyte levels. A, B. Plasma aldosterone and corticosterone levels in wild type and knock‐in mice. The indicated mice were fed a normal Na+‐diet (0.3%) or subjected to a restricted Na+‐diet (0.03%) for 2 weeks. Plasma aldosterone (A) and corticosterone (B) levels were measured in the indicated mice. *p < 0.0001 versus normal Na+‐diet. C, D. Urine sodium and potassium levels at indicated time intervals after mice are switched from a high salt diet to a low salt diet. The indicated mice were fed a high salt (3% Na+) diet for 1 week. Mice were then switched to a restricted low salt (0.03% Na+)‐diet. Urine samples were taken immediately before (0 h) or at the indicated times after switching diets and urinary sodium (C) and potassium (D) levels quantified. *p < 0.05 versus SPAK+/+. E. Expression of ENaC subunits in kidney extracts of wild type and knock‐in mice. The indicated membrane preparations (5 µg protein) derived from wild type and SPAK243A/243A mouse kidney were subjected to immunoblot analysis with the specified antibodies. Flotillin and Na‐K‐ATPase are membrane proteins whilst glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) is a cytosolic protein. Similar results were obtained in two separate experiments. Fatema H. Rafiqi et al. EMBO Mol Med. 2010;2:63-75 © as stated in the article, figure or figure legend