We have previously demonstrated that p1,p4-diadenosine 5′-tetraphosphate (Ap4A) induces the release of nitric oxide (NO) and modulates the uptake of extracellular L-arginine (L-Arg) and L-citrulline (L-Cit) by bovine aortic endothelial cells (BAEC) [Hilderman, R.H. and Christensen, E.F. (1998) FEBS Lett. 427, 320–324 and Hilderman, R.H., Casey, T.E. and Pojoga, L.H. (2000) Arch. Biochem. Biophys. 375, 124–130]. In this communication we report that extracellular Ap4A enhances the uptake of L-Arg and L-Cit through a pore on the plasma membrane of BAEC that is selective for these two amino acids. We also demonstrate that Ap2A, which induces NO release, enhances L-Arg uptake while Ap5A, a vasoconstrictor, does not enhance the uptake of L-Arg. The potential physiological significance of the uptake of these two amino acids in relation to NO synthesis is discussed.
