Sodium and cell rigidity

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Gwendolyn Foster
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1 Sodium and cell rigidity Hans Oberleithner Institute of Physiology II University Münster, Germany Calcium and the cytoskeleton, Minisymposium, Casapueblo, November 3, 2007; 11:30 a.m.

2 This is what we need This is what we eat

3 20,000 Deaths from stroke in Montevideo per year Uruguay Meneton et al; Physiol Rev 2005

4 Hypertension 2005; 45:

5 3g 6g 9g

6 Some physiology The mineralocorticoid hormone aldosterone controls salt transport in the kidney retains salt in the extracellular compartments and thus maintains arterial blood pressure.

7 Some more physiology Besides kidney, the cardiovascular system is a target for aldosterone Myocardium Vascular smooth muscle endothelium

8 Endothelium (Felix) imaged in fluid Image size: 180 x 180 µm Image resolution: 1024 x 1024 lines Time to obtain the image: 30 min Instrument: BioScope II from Veeco

9 Epithelial sodium channels (ENaC) are found in endothelia and they are upregulated by aldosterone = Na + = Ca 2+ amiloride binding ouside Ca 2+ cannot enter inside

10 1,250 ENaC found in the apical surface of an endothelial cell No aldosterone Kusche et al Pfügers Arch µm

11 1,750 ENaC found in the apical surface of an endothelial cell aldosterone +29% Kusche et al Pfügers Arch µm

12 Is salt an endothelial stiffener and is ENaC involved?

14 Force distance curves performed in a single endothelial cell

15 For details go to:

16 Endothelial cell stiffness? Extracellular sodium concentration (mm) low sodium normal sodium high sodium

17 Three force distance curves

18 laser deform cantilever AFM tip Cantilever deflection (nm) Δ 50 nm Δ 54 nm Δ 78 nm 200 nm 200 nm 200 nm 2. touch 1. approach 145 mm Na mm Na mm Na Cell membrane indentation depth Distance between AFM tip and cell surface nm

19 Change in endothelial cell stiffness (%) Oberleithner et al PNAS 2007 Eplerenone treated cells Aldosterone treated cells vertical force Extracellular sodium concentration (mm)

20 A rise in extracellular sodium transiently increases cell volume and the ENaC blocker amiloride prevents this response

21 A B Single cell line scan versus time h line scan height profile h 200 nm 1 min 135 Na mm Na + (constant osmolarity) D Transient increase in cell height (nm) Transient increase in cell height (nm) P = to 150 mm Na to 150 mm Na + + amiloride C Single cell line scan versus time height profile h < 50 nm 135 Na mm Na + + amiloride (const. osmolarity)

22 Amiloride prevents sodium-mediated cell stiffening

23 Change in endothelial cell stiffness (%) Human endothelium, pretreated with aldosterone Amiloride resistent Amil Amiloride sensitive Amil 135 mm sodium 150 mm sodium

24 High sodium reduces endothelial deformability

25 Force Scan

pretreated with aldosterone 2 µm 2 µm 135 mm sodium 150 mm sodium 0 20 40 60 80 µm 0

26 pretreated with aldosterone 2 µm 2 µm 135 mm sodium 150 mm sodium µm 0 soft stiff µm 2 µm 2 µm 25 µm A constant shear force of 5 nn is applied!

27 Is a stiff endothelial cell functionally inferior to a soft one?

29 Blood flow Deformation NO Vascular smooth muscle relaxes

30 Blood flow Deformability NO Blood vessel does not relax

analysis) flasks tilted rhythmically for 24h (creates shear forces) medium

31 Aortic endothelial cells GM 7373 (more NO metabolism) cultured in flasks little culture medium low/high sodium +/- aldosterone reduced in proteins (improves NO analysis) flasks tilted rhythmically for 24h (creates shear forces) medium filtered lyophilized resuspended nitrite measurement/griess reagent spectrophotometry

32 Nitrite concentration in the culture medium (µm) mm Na mm Na mm Na mm Na + + aldosterone + aldosterone * Oberleithner et al PNAS 2007

33 plasma sodium concentration increases beyond 140 mm in physiological conditions, i.e. that aldosterone is available sodium volume pulsatile force endothelial cell nitric oxide deformability vascular smooth muscle cell tension increases Oberleithner et al PNAS 2007

34 Δ sodium Δ volume Δ stiffness Δ NO Δ blood pressure

35 Δ sodium Δ volume Δ stiffness Δ NO Δ blood pressure

36 Hypertension 2005; 45:

38 Caipirinha

39 Where the hell is Münster? Germany

40 Münster

42 Physiology

43 Münster Christoph Riethmüller...NO Hermann Schillers...AFM Martin Hausberg...Hypertension Kristina Kusche-Vihrog...ENaC Graham MacGregor... Idea about sodium Hugh de Wardener... kept us going

Endothelial cells as vascular salt sensors

http://www.kidney-international.org & 21 International Society of Nephrology Endothelial cells as vascular salt sensors Hans Oberleithner 1, Kristina Kusche-Vihrog 1 and Hermann Schillers 1 1 Medical Faculty,