Volume 72, Issue 5, Pages 566-573 (September 2007) The role of the BK channel in potassium homeostasis and flow-induced renal potassium excretion  T. Rieg, V. Vallon, M. Sausbier, U. Sausbier, B. Kaissling, P. Ruth, H. Osswald  Kidney International  Volume 72, Issue 5, Pages 566-573 (September 2007) DOI: 10.1038/sj.ki.5002369 Copyright © 2007 International Society of Nephrology Terms and Conditions

Figure 1 Flow-induced renal potassium excretion. (a) UV, absolute (AE K+), and fractional (FE K+) urinary K+ excretion in two period (30 min each) clearance experiments in anesthetized WT (n=6) and BK−/− (n=5) mice under basal conditions and in response to the vasopressin V2R antagonist, SR 121463 (1 mg/kg i.v.). (b) In clearance experiments, a significant correlation was detected between UV and urinary K+ excretion (UKV) in WT but not in BK−/− mice. WT: n=12 data points, six mice before and after SR 121463; BK−/−: n=10 data points, five mice. (c) In a separate set of acute experiments (3 h) in metabolic cages, AE K+- and creatinine-related urinary K+ excretion were determined in awake WT (n=9) and BK−/− (n=7) treated with the vasopressin V2R antagonist, SR121463 (1 mg/kg i.p.). *P<0.05 vs WT; §P<0.05 vs basal same genotype. Kidney International 2007 72, 566-573DOI: (10.1038/sj.ki.5002369) Copyright © 2007 International Society of Nephrology Terms and Conditions

Figure 2 Potassium homeostasis in response to variation in potassium intake. Influence of control- (K+ 1%, control), low- (K+ <0.03%, low), or high-K+ diet (K+ 5%, high) for 6 days on absolute urinary (U) and fecal (F) (a and b) Na+ and K+ excretion, (c) UV, (d) plasma K+, and (e) aldosterone concentrations in 24 h metabolic cage experiments in WT (n=10) and BK−/− (n=8). *P<0.05 vs WT. Kidney International 2007 72, 566-573DOI: (10.1038/sj.ki.5002369) Copyright © 2007 International Society of Nephrology Terms and Conditions

Figure 3 Renal expression of BK channel α-subunit and ROMK channel under control- and high-K+ diet. (a) Western blots for renal expression of BK channel (molecular weight 125 kDa; 100 μg membrane proteins per lane) in WT mice under control- (left) and high-K+ diet (right); n=8 kidneys from 4 WT mice per diet. (b) Representative Western blots for renal expression of ROMK (molecular weight 45 kDa; 100 μg protein per lane) under control- and high-K+ diet in WT and BK−/− mice. ROMK expression was referred to MAPK 42/44 used as loading control; statistics from 5 WT (10 kidneys) or 4 BK−/− (8 kidneys) mice per diet. *P<0.05 vs control diet. Kidney International 2007 72, 566-573DOI: (10.1038/sj.ki.5002369) Copyright © 2007 International Society of Nephrology Terms and Conditions

Figure 4 Morphology and immunofluorescence for ROMK in mouse kidney cortex. Upper panel: 1-μm thin epon sections. The cortical distal tubular segments, in particular the CNT, show hypertrophy after 6 days of high-K+ diet; hypertrophy is less prominent in BK−/− than in WT mice. Lower panel: 5-μm thick cryostat sections. Immunofluorescence for ROMK shows a more prominent apical staining in BK−/− than in WT mice under control diet and even more so in response to a high-K+ diet; hypertrophy of CNT after 6 days of high-K+ diet is also apparent in the immunostainings for ROMK; the ROMK-negative cells in the epithelial lining are intercalated cells. Bar: ∼50 μm. Kidney International 2007 72, 566-573DOI: (10.1038/sj.ki.5002369) Copyright © 2007 International Society of Nephrology Terms and Conditions