Receptor-mediated activation of nitric oxide synthesis by arginine in endothelial cells

doi:10.1073/pnas.0506824104

Receptor-mediated activation of nitric oxide synthesis by arginine in endothelial cells

Departments of *Surgery and
^§Pathology, Louisiana State University Health Sciences Center, New Orleans, LA 70112;
^‡Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112; and
^¶Departments of Anesthesiology, Physiology, and Biophysics and Center for Free Radical Biology, University of Alabama at Birmingham, Birmingham, AL 35487

Edited by Salvador Moncada, University of London, London, United Kingdom, and approved May 1, 2007 (received for review August 8, 2005)

Abstract

Arginine contains the guanidinium group and thus has structural similarity to ligands of imidazoline and α-2 adrenoceptors (α-2 AR). Therefore, we investigated the possibility that exogenous arginine may act as a ligand for these receptors in human umbilical vein endothelial cells and activate intracellular nitric oxide (NO) synthesis. Idazoxan, a mixed antagonist of imidazoline and α-2 adrenoceptors, partly inhibited l-arginine-initiated NO formation as measured by a Griess reaction. Rauwolscine, a highly specific antagonist of α-2 AR, at very low concentrations completely inhibited NO formation. Like l-arginine, agmatine (decarboxylated arginine) also activated NO synthesis, however, at much lower concentrations. We found that dexmedetomidine, a specific agonist of α-2 AR was very potent in activating cellular NO, thus indicating a possible role for α-2 AR in l-arginine-mediated NO synthesis. d-arginine also activated NO production and could be inhibited by imidazoline and α-2 AR antagonists, thus indicating nonsubstrate actions of arginine. Pertussis toxin, an inhibitor of G proteins, attenuated l-arginine-mediated NO synthesis, thus indicating mediation via G proteins. l-type Ca²⁺ channel blocker nifedipine and phospholipase C inhibitor U73122 inhibited NO formation and thus implicated participation of a second messenger pathway. Finally, in isolated rat gracilis vessels, rauwolscine completely inhibited the l-arginine-initiated vessel relaxation. Taken together, these data provide evidence for binding of arginine to membrane receptor(s), leading to the activation of endothelial NO synthase (eNOS) NO production through a second messenger pathway. These findings provide a previously unrecognized mechanistic explanation for the beneficial effects of l-arginine in the cardiovascular system and thus provide new potential avenues for therapeutic development.

Footnotes

^†To whom correspondence should be addressed at:
Department of Physics, Wake Forest University, Winston-Salem, NC 27109.
E-mail: mjoshi20{at}yahoo.com
Author contributions: M.S.J. and J.R.L. designed research; M.S.J., F.K.J., and R.A.J. performed research; M.S.J., T.B.F., S.P., and J.R.L. analyzed data; and M.S.J. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

α-2 AR,

α-2 adrenoceptor;

eNOS,

endothelial NOS;

HUVEC,

human umbilical vein endothelial cell;

I-receptor,

imidazoline receptor;

IP3,

inositol-1,4,5-triphosphate;

NOS,

NO synthase.