Stretch-induced morphological changes of human endothelial cells depend on the intracellular level of Ca2+ rather than of cAMP

When exposed to a uni-axial cyclic stretch, cultured human umbilical vein endothelial cells (HUVECs) align and elongate perpendicular to the stretch axis. Previous studies showed that forskolin inhibited stretch-induced orientation of endothelial cells, suggesting that adenosine 3:5-cyclic monophosphate (cAMP) plays an important role in the shape change. However, we have recently shown that stretch-induced shape changes in cultured HUVECs are due to increased Ca2+]i. In the present study, we examined the possible role of cAMP in stretch-induced shape changes in cultured HUVECs. Application of uni-axial cyclic stretch induced a gradual rise in cAMP reaching a peak level at 60 min after the onset of stretch. The adenylate cyclase activator, forskolin, increased the basal level of cAMP but inhibited the rise in Ca2+]i resulting in no cell shape changes. In contrast, N 6,2-dibutyryladenosine 3:5-cyclic monophosphate (dbcAMP) enhanced the stretch-induced increase in cAMP and Ca2+]i and resulted in cell shape changes. On the other hand, 2'5'-dideoxyadenosine (DDA), an adenylate cyclase inhibitor, inhibited stretch-induced increases in cAMP and Ca2+]i resulting in no cell shape changes. In summary, our data showed that cell shape changes were consistently dependent on Ca2+]i rather than cAMP levels. We conclude that the primary second messenger in the stretch-induced shape changes in HUVECs is intracellular Ca2+ rather than cAMP.