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

1 To investigate the quantitative relationship between elevation in the int racellular Ca2+ concentration ([Ca2+](i)) and nitric oxide (NO) production, the changes in [Ca2+](i) and NO production were determined in parallel, us ing fluorimetry of fura-2 and 2,3-diaminonaphthalene, respectively, in endo thelial cells ex vivo of pig aortic valves. 2 The extent of [Ca2+](i) elevation was quantitatively assessed by two para meters: 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 mu M ATP for 3 min. 3 ATP, bradykinin, thrombin, and ionomycin were used as stimulation to indu ce NO production, and all these caused [Ca2+](i) increases and NO productio n in a concentration-dependent manner. 4 The relationships between the peak [Ca2+](i) and NO production or between the integrated [Ca2+](i) elevation and NO production were well described b y a straight line. However, the slope value of the linear relationship in b oth cases Varied with the type of stimulation, with thrombin giving the gre atest value, followed by ATP, bradykinin and ionomycin. 5 These data suggest that in endothelial cells ex vivo: (1) [Ca2+](i) eleva tion regulates NO production, but (2) the peak [Ca2+](i) elevation- or the integrated [Ca2+]. elevation-NO production relationships varies depending o n the type of agonists. Our results thus demonstrate the presence of the ag onists-dependent modulation of the relationship between [Ca2+](i) elevation and NO production in endothelial cells ex vivo.