title: Disruption of Na+,HCO₃⁻ cotransporter NBCn1 (slc4a7) inhibits NO-mediated vasorelaxation, smooth muscle Ca²⁺ sensitivity, and hypertension development in mice.
abstract: BACKGROUND
  Disturbances in pH affect artery function, but the mechanistic background remains controversial. We investigated whether Na(+), HCO₃- transporter NBCn1, by regulating intracellular pH(pH₁), influences artery function and blood pressure regulation.
  
  
  RESULTS
  Knockout of NBCn1 in mice eliminated Na+, HCO₃⁻ cotransport and caused a lower steady-state pH(i) in mesenteric artery smooth muscle and endothelial cells in situ evaluated by fluorescence microscopy. Using myography, arteries from NBCn1 knockout mice showed reduced acetylcholine-induced NO-mediated relaxations and lower rho-kinase-dependent norepinephrine-stimulated smooth muscle Ca²⁺ sensitivity. Acetylcholine-stimulated NO levels (electrode measurements) and N-nitro-l-arginine methyl ester-sensitive l-arginine conversion (radioisotope measurements) were reduced in arteries from NBCn1 knockout mice, whereas relaxation to NO-donor S-nitroso-N-acetylpenicillamine, acetylcholine-induced endothelial Ca²⁺ responses (fluorescence microscopy), and total and Ser-1177 phosphorylated endothelial NO-synthase expression (Western blot analyses) were unaffected. Reduced NO-mediated relaxations in arteries from NBCn1 knockout mice were not rescued by superoxide scavenging. Phosphorylation of myosin phosphatase targeting subunit at Thr-850 was reduced in arteries from NBCn1 knockout mice. Evaluated by an in vitro assay, rho-kinase activity was reduced at low pH. Without CO₂/HCO₃⁻, no differences in pH(i), contraction or relaxation were observed between arteries from NBCn1 knockout and wild-type mice. Based on radiotelemetry and tail-cuff measurements, NBCn1 knockout mice were mildly hypertensive at rest, displayed attenuated blood pressure responses to NO-synthase and rho-kinase inhibition and were resistant to developing hypertension during angiotensin-II infusion.
  
  
  CONCLUSIONS
  Intracellular acidification of smooth muscle and endothelial cells after knockout of NBCn1 inhibits NO-mediated and rho-kinase-dependent signaling in isolated arteries and perturbs blood pressure regulation.
authors.affiliation: Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark. eb@fi.au.dk
authors.forename: Ebbe
authors.initials: E
authors.lastname: Boedtkjer
authors.forename: Jeppe
authors.initials: J
authors.lastname: Praetorius
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Matchkov
authors.forename: Edgaras
authors.initials: E
authors.lastname: Stankevicius
authors.forename: Susie
authors.initials: S
authors.lastname: Mogensen
authors.forename: Annette C
authors.initials: AC
authors.lastname: Füchtbauer
authors.forename: Ulf
authors.initials: U
authors.lastname: Simonsen
authors.forename: Ernst-Martin
authors.initials: EM
authors.lastname: Füchtbauer
authors.forename: Christian
authors.initials: C
authors.lastname: Aalkjaer
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000235:genetics; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D006973:Hypertension / Q000235:genetics / Q000378:metabolism / Q000517:prevention & control*; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000503:physiopathology*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors* / Q000502:physiology*; D009924:Organ Culture Techniques; D027982:Sodium-Bicarbonate Symporters / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
chemical_list: C498902:Slc4a7 protein, rat; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D009569:Nitric Oxide; D002118:Calcium