Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark.
Circulation. 2011 Oct 25;124(17):1819-29. doi: 10.1161/CIRCULATIONAHA.110.015974. Epub 2011 Sep 26.
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.
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.
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.
pH 值的改变会影响动脉功能，但其中的机制仍存在争议。我们研究了 NBCn1（一种 Na⁺、HCO₃⁻共转运蛋白）是否通过调节细胞内 pH 值（pH₁）影响动脉功能和血压调节。
在小鼠中敲除 NBCn1 消除了 Na⁺、HCO₃⁻共转运，并通过荧光显微镜原位评估，导致其肠系膜动脉平滑肌和内皮细胞的稳态 pH(i)降低。使用血管环法，发现 NBCn1 敲除小鼠的动脉对乙酰胆碱诱导的一氧化氮（NO）介导的舒张反应减弱，且对 rho 激酶依赖性去甲肾上腺素刺激的平滑肌 Ca²⁺敏感性降低。在 NBCn1 敲除小鼠的动脉中，乙酰胆碱刺激的 NO 水平（电极测量）和 N-硝基-L-精氨酸甲酯敏感的 L-精氨酸转化（放射性同位素测量）降低，而对 NO 供体 S-亚硝基-N-乙酰青霉胺的舒张作用、乙酰胆碱诱导的内皮细胞 Ca²⁺反应（荧光显微镜）以及内皮型一氧化氮合酶的总表达和 Ser-1177 磷酸化（Western blot 分析）均不受影响。在 NBCn1 敲除小鼠的动脉中，NO 介导的舒张作用降低，不能通过超氧化物清除得到挽救。肌球蛋白磷酸酶靶向亚单位 Thr-850 的磷酸化在 NBCn1 敲除小鼠的动脉中减少。在体外测定中，低 pH 值时 rho 激酶的活性降低。在没有 CO₂/HCO₃⁻的情况下，NBCn1 敲除和野生型小鼠的动脉在 pH(i)、收缩或舒张方面均无差异。基于无线电遥测和尾套测量，NBCn1 敲除小鼠在休息时轻度高血压，对一氧化氮合酶和 rho 激酶抑制的血压反应减弱，并且在血管紧张素 II 输注期间不易发生高血压。
NBCn1 敲除后平滑肌和内皮细胞的细胞内酸化抑制了分离动脉中的 NO 介导和 rho 激酶依赖性信号转导，并扰乱了血压调节。
