PLATELET AGONISTS AND CALCIUM HOMEOSTASIS IN ENDOTHELIAL-CELLS - POSSIBLE ROLE IN THE INTERACTION OF ENDOTHELIUM WITH HEMOSTATIC SYSTEM

Background and Objective. The endothelium is a complex tissue that mod ulates a vast array of biological functions and Ca++ transients are cr itically important to these endothelium-dependant functions. We addres sed the hypothesis that some platelet agonists and products of activat ion of the hemostatic system could determine Ca++ transients in a bovi ne pulmonary artery endothelial cell line (CPA-47). Design and Methods . The effect of thrombin, collagen, ADP, PAF, PDGF, GRGDS, and the TxA (2) mimetic U46619 on CPA-47-cytoplasmic Ca++ transients was evaluated using a Platelet lonized Calcium Aggregometer, after cells were loade d with the photoprotein aequorin. Results. ADP, GRGDS, PAF, U46619 and collagen were able to induce rapid Ca++ transients in CPA-47 endothel ial cells and the response was stable after repeated additions, while thrombin acted slightly differently, as cells became refractory to thi s agonist after the first response, but they remained sensitive to the other inducers. Only PDGF was completely ineffective. Furthermore, ca lcium-channel blockers verapamil and flunarizine (but not nifedipine) caused a reduction only of thrombin-induced cytoplasmic Ca++ transient s, while the addition of depolarizing concentration of KCI suggests th e presence also of voltage-operated channels on endothelial cell membr ane. Finally, EGTA caused the complete suppression of Ca++ transients induced by all the tested agonists but collagen. Interpretation and Co nclusions. Our study demonstrated that the different agents tested are able to induce Ca++ transients on bovine endothelial cultured cells, similarly to that observed in platelets and other non excitable cells, including tumor cells, and that calcium channel blockers had only a l imited inhibitory effect on these changes; these results may help more thorough understanding of the biochemical basis of the interaction be tween endothelium and the hemostatic system. (C)1998, Ferrata Storti F oundation.