Increased flow-induced ATP release from isolated vascular endothelial cells but not smooth muscle cells

1. Freshly harvested smooth muscle cells and endothelial cells isolated from the rabbit aorta were perfused (0.5 ml min-1) and stimulated twice by an increase of flow rate (3.0 ml min-1) in order to compare their ability to release adenosine 5'-triphosphate (ATP). 2. In smooth muscle cells, the basal release of ATP (0.0265 +/- 0.0033 pmol ml-1 per 10(6) cells) was not increased during periods of increased flow (P = 0.2). 3. In endothelial cells, the concentration of ATP in the perfusate during periods of low flow (0.0335 +/- 0.0038 pmol ml-1 per 10(6) cells) was significantly increased by 14 times and 5 times during the first and second periods of increased flow, respectively. 4. The release of ATP by endothelial cells did not appear to be caused by the lysis of cells during the period of increased flow because it can be reproduced several times and because there was no difference between lactate dehydrogenase activity in perfused cells and that in non-perfused cells. 5. These results show that, of the two major cell types of the vascular wall, only endothelial cells react to shear stress by releasing ATP.