Background and purpose: Experiments were designed to assess whether or not the intracellular concentration of calcium and reactive oxygen species (ROS) increase in endothelial cells of the rat thoracic aorta in response to releasers of endothelium-derived contracting factor (EDCF) and if so, whether or not a difference exists between spontaneously hypertensive (SHR) and normotensive (WKY) rats.
Experimental approach: Calcium and ROS were measured by confocal microscopy, using Fura-red in combination with Fluo-4 and dichlorodihydrofluorescein diacetate, respectively.
Key results: Acetylcholine caused a rapid increase in cytosolic calcium concentration in endothelial cells of both SHR and WKY, which was significantly more pronounced in aortae of the former strain. This rise of calcium was not affected by indomethacin (an inhibitor of cyclooxygenase) or Tiron plus diethyldithiocarbamate acid (DETCA) (membrane permeable antioxidants). In the presence of a nitric oxide synthase blocker, acetylcholine also caused a rapid increase in ROS in endothelial cells of SHR but not in those of WKY. The burst of ROS was prevented by indomethacin or Tiron plus DETCA.
Conclusions and implications: These experiments show that endothelial cells of SHR are more prone to calcium and ROS overload upon stimulation with acetylcholine. The abnormal accumulation of calcium is a prerequisite to initiate the release of EDCF and can be mimicked using the calcium ionophore A23187. The sequence of events occurring during endothelium-dependent contractions firstly requires the accumulation of calcium, which then activates cyclooxygenase and produces ROS along with EDCF that in turn stimulates TP-receptors, resulting in EDCF-mediated contractions.