1 ATP and ATP analogues induced prostacyclin (PGI2) secretion from human cultured umbilical vein endothelial cells. 2 The threshold active concentration for ATP was <1 M. The rank order of potency of analogues was 2-chloroadenosine 5'-triphosphate (2-CIATP) > 2-methylthioadenosine 5'-triphospate (2-MeSATP) > ATP > ADP, while adenosine 5'-(a, f-methylene)triphosphonate, AMP and adenosine were inactive, indicating the presence of P2Y-purinoceptors.3 In contrast to their actions on P2y-receptors in guinea-pig taenia coli, isopolar analogues of 2-methylthioadenosine 5'-(fB, y-methylene)triphosphonate were less effective than ATP. 4 ATP and ATP analogues increased intracellular free calcium ions, [Ca2+]i, giving a rapid transient peak due predominantly to release from intracellular stores, followed by a maintained steadystate elevated level due to influx.

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