Disruption of NA +,HCO 3- cotransporter NBCn1 (slc4a7) Inhibits no-mediated vasorelaxation, smooth muscle ca 2+ 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 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 Ca 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 Ca 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. © 2011 American Heart Association, Inc.