Disruption of Na+,HCO3− Cotransporter NBCn1 (slc4a7) Inhibits NO-Mediated Vasorelaxation, Smooth Muscle Ca2+ Sensitivity, and Hypertension Development in Mice
Background—Disturbances in pH affect artery function, but the mechanistic background remains controversial. We investigated whether Na+,HCO3− cotransporter NBCn1, by regulating intracellular pH (pHi), influences artery function and blood pressure regulation.
Methods and Results—Knockout of NBCn1 in mice eliminated Na+,HCO3− cotransport and caused a lower steady-state pHi 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 pHi, 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.
- Received December 21, 2010.
- Accepted August 8, 2011.
- © 2011 American Heart Association, Inc.