Na+–Ca2+ exchanger contributes to Ca2+extrusion in ATP-stimulated endothelium of intact rat aorta

The role of Na+–Ca2+ exchanger (NCX) in vascular endothelium is still matter of debate. Depending on both the endothelial cell (EC) type and the extracellular ligand, NCX has been shown to operate in either the forward (Ca2+ out)- or the reverse (Ca2+ in)-mode. In particular, acetylcholine (Ach) has been shown to promote Ca2+ inflow in the intact endothelium of excised rat aorta. Herein, we assessed the involvement of NCX into the Ca2+ signals elicited by ATP in such preparation. Removal of extracellular Na+ (0Na+) causes the NCX to switch into the reverse-mode and induced an increase in intracellular Ca2+ concentration ([Ca2+]i), which disappeared in the absence of extracellular Ca2+, and in the presence of benzamil, which blocks both modes of NCX, and KB-R 7943, a selective inhibitor of the reverse-mode. ATP induced a transient Ca2+ signal, whose decay was significantly prolonged by 0Na+, benzamil, DCB, and monensin while it was unaffected by KB-R 7943. Notably, lowering extracellular Na+ concentration increased the sensibility to lower doses of ATP. These date suggest that, unlike Ach-stimulated ECs, NCX promotes Ca2+ extrusion when the stimulus is provided by ATP in intact endothelium of rat aorta. These data show that, within the same preparation, NCX operates in both modes, depending on the chemical nature of the extracellular stimulus.