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To investigate whether the resting cytosolic free calcium concentration and the agonist-induced increase in this concentration in vascular endothelial cells from spontaneously hypertensive rats (SHR) differ from those in normotensive Wistar-Kyoto (WKY) rats.The Fura-2 fluorescence technique was used to monitor changes in cytosolic free calcium concentration in isolated aortic endothelial cells from SHR (aged 12 weeks) and age-matched WKY rats.Aortic endothelial cells from primary culture to the third passage were used. The cells were grown to a confluent monolayer on coverslips before the fluorescent measurement of cytosolic free calcium concentration. The resting cytosolic free calcium concentration and changes in it induced by bradykinin, endothelin 1, angiotensin II and thapsigargin were examined and compared between endothelial cells from SHR and WKY rats.The resting cytosolic free calcium concentration in aortic endothelial cells was significantly lower in SHR than in WKY rats. Bradykinin induced a lesser increase in cytosolic free calcium concentration in endothelial cells from SHR than in those from WKY rats. However, aortic endothelial cells both from SHR and from WKY rats had a similar calcium response to endothelin 1 and angiotensin II. Furthermore, the thapsigargin-induced increase in cytosolic free calcium concentration was significantly less in SHR than in WKY rat endothelial cells. These results suggest that the altered calcium response to bradykinin in endothelial cells from SHR could be caused by an alteration of bradykinin receptors or changed bradykinin degradation. Alternatively, the intracellular calcium stores that are sensitive to thapsigargin and bradykinin may differ from those that are activated by endothelin 1 and angiotensin II in SHR aortic endothelial cells.A lower level of resting cytosolic free calcium concentration and the impaired bradykinin-induced increases in it in SHR endothelial cells could reflect dysfunction of vascular endothelium underlying a reduced endothelium-dependent vasorelaxation in this genetic hypertension model.