Effect of shear stress on the release of soluble ecto-enzymes ATPase and 5′-nucleotidase along with endogenous ATP from vascular endothelial cells

1 Stimulation of endothelial cells from human umbilical vein by shear stress induced release of endogenous ATP which was accompanied by an extracellular increase in the activity of enzymes degrading both ATP (ATPases) and AMP (5'-nucleotidases). 2 The activity of soluble ATPase was progressively increased from 1.62 +/- 0.27 to 12.7 +/- 1.0 pmoles ml(-1) h(-1) after 60 min of stimulation by shear stress. 3 The rate of [(3)H]-ATP hydrolysis in the medium was inhibited by the purinergic agents suramin, Reactive blue 2 and pyridoxalphosphate-6-azophenyl-2'4'-disulphonic acid, and remained insensitive to the classic inhibitors of ion-pumping and intracellular ATPases. 4 Shear stress also increased the activity of 5'-nucleotidase in the medium from 2.0+/-0.5 to 27.2+/-2.8 pmoles ml(-1) h(-1). When shear stress was applied after removal of ecto-5'-nucleotidase by phosphatidylinositol-specific phospholipase C, the release of 5'-nucleotidase was drastically reduced. 5 These results show that soluble ATPase and 5'-nucleotidase which are released during shear stress are not released from an intracellular compartment together with ATP but have an extracellular origin.