Calcium-dependent synthesis of prostacyclin in ATP-stimulated venous endothelial cells

Prostacyclin is a powerful vasodilator that is released from vascular endothelial cells. Previous studies in our laboratory have indicated that arachidonic acid metabolites from venous endothelium play an important role in the dilation of adjacent arterioles during muscle stimulation. Furthermore, recent studies have suggested that ATP released from red blood cells during hypoxia stimulates dilation of arterioles. We tested the hypothesis that an ATP-induced increase in intracellular Ca2+ in venous endothelium promotes prostacyclin synthesis. Small branches of femoral veins were isolated from male golden hamsters, placed in a 1 mL bath, and cannulated for perfusion with 3-(N-morpholino) propanesulfonic acid (MOPS)-buffered physiological salt solution at 37degreesC. Prostacyclin synthesis was determined by enzyme immunoassay of bath solution. Perfusion of veins with ATP increased prostacyclin synthesis from 50 +/- 5 to 627 +/- 46 pg/mL (n=49). ATP-induced prostacyclin synthesis was inhibited by removal of extracellular Ca2+, chelation of intracellular Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) (10 mumol/L for 10 minutes), and preincubation with cytosolic phospholipase A(2) (PLA(2)) inhibitors, AACOCF(3), and bromoenol lactone. Changes in intracellular Ca2+ in cultured human venous endothelial cells were assessed by fura-2 spectrofluorometry. ATP induced a transient Ca2+ peak within seconds, and the subsequent Ca2+ plateau was abolished by removal of extracellular Ca2+. An increase in prostacyclin synthesis was detected in these cells 2 minutes after application of ATP. These findings suggest that the ATP-induced increase in intracellular Ca2+ stimulates prostacyclin synthesis in venous endothelial cells.