Abstract
The barrier function of the endothelium is controlled by the second messengers Ca2+ and cAMP that differentially regulate the permeability of endothelial cells. The Ca2+-elevating agent thrombin has been demonstrated to increase endothelial permeability and to decrease cAMP levels as detected via enzyme immunoassays. To study the effects of thrombin on cAMP with high temporal resolution, we utilised the FRET-based cAMP sensor Epac1-camps in single intact human umbilical vein endothelial cells (HUVECs). In these cells, thrombin induced a delayed increase in [cAMP], initiating after about 40 s, with maximum cAMP levels after 130 s of thrombin application. This increase of cAMP levels was Ca2+-dependent, but did not require calmodulin (CaM). Pharmacological approaches revealed that phospholipase A2 (PLA2) activity and cyclooxygenase (COX)-mediated synthesis of prostaglandins was required for the thrombin-induced elevation of [cAMP]. Furthermore, preincubation of HUVECs with a prostacyclin-receptor antagonist significantly reduced the thrombin-induced increase in [cAMP]. We conclude that thrombin causes the synthesis of prostacyclin in endothelial cells and that the subsequent stimulation of Gs-coupled prostacyclin receptors then results in an increase in [cAMP].