NANOMOLAR LEVEL OF OUABAIN INCREASES INTRACELLULAR CALCIUM TO PRODUCE NITRIC OXIDE IN RAT AORTIC ENDOTHELIAL CELLS

• Published in: Clinical and experimental pharmacology & physiology 2004-05, Vol.31 (5-6), p.276-283
• Main Authors: Dong, Xian Hui, Komiyama, Yutaka, Nishimura, Noriko, Masuda, Midori, Takahashi, Hakuo
• Format: Article
• Language: English
• Subjects: Animals; Aorta, Thoracic - drug effects; Aorta, Thoracic - metabolism; Bradykinin - pharmacology; Ca2+ exchange; Calcium - metabolism; Cells, Cultured; Dose-Response Relationship, Drug; Endothelium, Vascular - drug effects; Endothelium, Vascular - metabolism; intracellular calcium; Intracellular Fluid - drug effects; Intracellular Fluid - physiology; K+-ATPase; Na+; nitric oxide; Nitric Oxide - biosynthesis; ouabain; Ouabain - administration & dosage; Rats; Rats, Sprague-Dawley
• ISSN: 0305-1870; 1440-1681
• DOI: 10.1111/j.1440-1681.2004.03995.x

Summary 1. Changes in [Ca2+]i across the cell membrane and/or the sarcoplasmic reticulum regulate endothelial nitric oxide (NO) synthase activity. 2. In the present study, we investigated the effect of ouabain, a specific inhibitor of Na+/K+‐ATPase, on NO release and [Ca2+]i movements in cultured rat aortic endothelial cells (RAEC) by monitoring NO production continuously using an NO‐specific real‐time sensor and by measuring the change in [Ca2+]i using a fluorescence microscopic imaging technique with high‐speed wavelength switching. The t½ (half‐time of the decline of [Ca2+]i to basal levels after stimulation with 10 µmol/L bradykinin) was used as an index of [Ca2+]i extrusion. 3. A very low concentration of ouabain (10 nmol/L) did not increase the peak of NO production, but decreased the decay of NO release and, accordingly, increased integral NO production by the maximal dose–response concentration induced by bradykinin. The same dose of ouabain affected [Ca2+]i movements across the cell membrane and/or sarcoplasmic reticulum induced by bradykinin with a time‐course similar to that of NO release. Moreover, the t½ was significantly increased. 4. Pretreatment of RAEC with Na+‐free solution, an inhibitor of the Na+/Ca2+ exchanger, and nickel chloride hexahydrate prevented the effects induced by bradykinin and ouabain. 5. These observations using real‐time recording indicate that a small amount of ouabain contributes to the bradykinin‐stimulated increase of NO production through inhibition of plasma membrane Na+/K+‐ATPase activity and an increase in intracellular Na+ concentrations. The membrane was then depolarized, leading to a decline in the bradykinin‐stimulated increase in [Ca2+]i by forward mode Na+/Ca2+ exchange to prolong the Ca2+ signal time. 6. From these results, we suggest that nanomolar levels of ouabain modulate [Ca2+]i movements and NO production in RAEC.