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      Pulsatile and Steady Flow-Induced Calcium Oscillations in Single Cultured Endothelial Cells


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          The influence of flow-imposed shear stress on the intracellular calcium concentration ([Ca<sup>2+</sup>]i) of cultured endothelial cells (ECs) remains incompletely understood. In the present study, we measured [Ca<sup>2+</sup>]i in single bovine aortic ECs, using fluorescence ratiometric image analysis. The effects of several flow patterns were analysed: steady shear stress (5–70 dyn/cm<sup>2</sup>), 1-Hz pulsatile shear stress (nonreversing 40 ± 20 dyn/cm<sup>2</sup>, reversing 20 ± 40 dyn/cm<sup>2</sup>, or purely oscillatory 0 ± 20 dyn/cm<sup>2</sup>), or changing shear stress levels. Under all flow conditions, single-cell analyses revealed flow-induced asynchronous [Ca<sup>2+</sup>]i oscillations, which occurred randomly over the monolayer and which were not seen in the average [Ca<sup>2+</sup>]i signal corresponding to the monolayer response. The number of single-cell [Ca<sup>2+</sup>]i oscillations and the corresponding oscillation frequency rose as the shear stress associated with the steady flow increased: 0.06 ± 0.02 min<sup>–1</sup> at 5 dyn/cm<sup>2</sup>, 0.19 ± 0.03 min<sup>–1</sup> at 20 dyn/cm<sup>2</sup>, and 0.28 ± 0.02 min<sup>–1</sup> at 70 dyn/cm<sup>2</sup> (means ± SD). Also, the number of oscillations was greater for any type of pulsatile flow (0.53 ± 0.07 min<sup>–1</sup> at 40 ± 20 dyn/cm<sup>2</sup>,0.54 ± 0.08 min<sup>–1</sup> at 20 ± 40 dyn/cm<sup>2</sup>, and 0.39 ± 0.07 min<sup>–1</sup> at 0 ± 20 dyn/cm<sup>2</sup>), as compared to any level of steady flow. The most dramatic finding was that purely oscillatory flow induced numerous single-cell [Ca<sup>2+</sup>]i oscillations, yet the average [Ca<sup>2+</sup>]i response for the monolayer did not change. Furthermore, an EC monolayer switched from low to high (or from high to low) steady flow consistently showed an increase (or a decrease) in the number of single-cell [Ca<sup>2+</sup>]i oscillations. These experiments show that ECs respond to different flow conditions by varying single-cell [Ca<sup>2+</sup>]i oscillatory activity. This may have important implications in the endothelium-dependent control of vascular physiology, such as the release of vasoactive substances.

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          Author and article information

          J Vasc Res
          Journal of Vascular Research
          S. Karger AG
          24 September 2008
          : 33
          : 5
          : 360-369
          School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Ga., Division of Cardiology, University of Washington, Seattle, Wash., USA
          159164 J Vasc Res 1996;33:360–369
          © 1996 S. Karger AG, Basel

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          Page count
          Pages: 10
          Research Paper


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