SIMULTANEOUS MEASUREMENTS OF CA2-OXIDE IN BRADYKININ-STIMULATED VASCULAR ENDOTHELIAL-CELLS( AND NITRIC)

The production of endothelium-derived relaxing factor (EDRF), known to be nitric oxide (NO), is triggered by a rise in the cytoplasmic calci um concentration ([Ca2+](i)) subsequent to receptor binding of vasoact ive agonists. In vascular endothelial cells, NO is synthesized from L- arginine by the Ca2+/calmodulin-dependent NO synthase. In this study, we report the first simultaneous measurements of [Ca-i(2+]) and [NO] a t the level of single endothelial cells. In cultured bovine aortic end othelial cells, extracellular application of bradykinin (BK, 10 to 20 mu mol/L) caused transient (sometimes oscillatory) increase in [Ca2+]( i), which was measured with the fluorescent Ca2+ indicator fura 2 and fluorescence imaging microscopy. BK caused an increase in [Ca2+](i), p rimarily through release from intracellular stores. Under identical ex perimental conditions, BK caused a transient increase in [NO], which w as measured by application of a porphyrinic NO microsensor. [NO] peake d at approximate to 0.5 mu mol/L. Simultaneous measurements of [Ca2+]( i) and [NO] in BK-stimulated endothelial cells revealed that a transie nt increase in [Ca2+](i) was rapidly followed by an increase in [NO] t hat outlasted the [Ca2+](i) transient.