The Effect of Extracellular pH Changes on Intracellular pH and Nitric Oxide Concentration in Endothelial and Smooth Muscle Cells from Rat Aorta

Aims: It has been known for more than a century that pH changes can alter vascular tone. However, there is no consensus about the effects of pH changes on vascular response. In this study, we investigated the effects of extracellular pH (pH(o)) changes on intracellular pH (pH(i)) and intracellular nitric oxide concentration ([NO](i)) in freshly isolated endothelial cells and cross sections from rat aorta. Main Methods: The HCl was used to reduce the pH(o) from 7.4 to 7.0 and from 7.4 to 6.5; the NaOH was used to increase the pHo from 7.4 to 8.0 and from 7.4 to 8.5. The fluorescent dyes 5-(and-6)-carboxy SNARF-1, acetoxymethyl ester, acetate (SNARF-1) and diaminofluorescein-FM diacetate (DAF-FM DA) were employed to measure the pH(i) and [NO](i), respectively. The fluorescence intensity was measured in freshly isolated endothelial cells by flow cytometry and in freshly obtained aorta cross sections by confocal microscopy. Key Findings: The endothelial and vascular smooth muscle pH(i) was increased at pH(o) 8.5. The extracellular acidification did not change the endothelial pH(i), but the smooth muscle pH(i) was reduced at pH(o) 7.0. At pH(o) 8.5 and pH(o) 6.5, the endothelial [NO](i) was increased. Both extracellular alkalinization and acidification increased the vascular smooth muscle [NO](i). Significance: Not all changes in pH(o) did result in pH(i) changes, but disruption of acid-base balance in both directions induced NO synthesis in the endothelium and/or vascular smooth muscle.