SYNERGISTIC EFFECT OF ACUTE-HYPOXIA ON FLOW-INDUCED RELEASE OF ATP FROM CULTURED ENDOTHELIAL-CELLS

Human umbilical vein endothelial cells (HUVECs) in primary cultures we re perfused under normoxic or hypoxic conditions. These cells were sti mulated twice for 3 min by increased flow (from 0.5 to 3.0 ml/min). Un der hypoxic conditions the basal release of ATP was the same as under normoxic conditions, but during increased flow the release was greater (0.58 +/- 0.07 > 0.32 +/- 0.04 pmoles/ml/10(6) cells ( +78%), for the first period of stimulation; 0.39 +/- 0.05 > 0.22 +/- 0.03 pmoles/ml/ 10(6) cells ( +79%) for the second period). Further experiments with s equential increments in flow rate showed that under both normoxic and hypoxic conditions, a positive correlation existed between ATP release and the rate of flow but there was always more ATP released under hyp oxic conditions regardless of the flow rate. HUVECs in secondary cultu re (second passage) were similarly stimulated. No differences were obs erved between normoxic and hypoxic conditions. In both cases, the quan tity of ATP released during high flow (0.050 +/- 0.004 pmoles/ml/10(6) cells) was significantly smaller than the quantity of ATP released du ring low flow (0.09 +/- 0.01 pmoles/ml/10(6) cells). To conclude, sinc e hypoxia alone did not affect ATP release, there appears to be a syne rgistic relationship between increased shear stress and hypoxia in the stimulation of ATP release from HUVECs. Moreover, the release of ATP under these conditions seems to be a property of highly differentiated endothelial cells.