Stimulus‐specific alteration of the relationship between cytosolic Ca2+ transients and nitric oxide production in endothelial cells ex vivo

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Abstract
To investigate the quantitative relationship between elevation in the intracellular Ca2+ concentration ([Ca2+]i) and nitric oxide (NO) production, the changes in [Ca2+]i and NO production were determined in parallel, using fluorimetry of fura‐2 and 2,3‐diaminonaphthalene, respectively, in endothelial cells ex vivo of pig aortic valves. The extent of [Ca2+]i elevation was quantitatively assessed by two parameters: the level of peak [Ca2+]i elevation and the area under the [Ca2+]i curve during treatment (the integrated [Ca2+]i elevation). The amount of NO production was expressed as a percentage of that obtained with 10 μM ATP for 3 min. ATP, bradykinin, thrombin, and ionomycin were used as stimulation to induce NO production, and all these caused [Ca2+]i increases and NO production in a concentration‐dependent manner. The relationships between the peak [Ca2+]i and NO production or between the integrated [Ca2+]i elevation and NO production were well described by a straight line. However, the slope value of the linear relationship in both cases varied with the type of stimulation, with thrombin giving the greatest value, followed by ATP, bradykinin and ionomycin. These data suggest that in endothelial cells ex vivo: (1) [Ca2+]i elevation regulates NO production, but (2) the peak [Ca2+]i elevation‐ or the integrated [Ca2+]i elevation‐NO production relationships varies depending on the type of agonists. Our results thus demonstrate the presence of the agonists‐dependent modulation of the relationship between [Ca2+]i elevation and NO production in endothelial cells ex vivo. British Journal of Pharmacology (2000) 130, 1140–1146; doi:10.1038/sj.bjp.0703420