Nitric-Oxide-Induced Vasodilatation: Regulation by Physiologic S-Glutathiolation and Pathologic Oxidation of the Sarcoplasmic Endoplasmic Reticulum Calcium ATPase

Nitric-oxide (NO)-induced vasodilatation is impaired in patients with a variety of cardiovascular diseases. Cyclic GMP, the principal mediator of NO-induced smooth muscle relaxation, usually functions normally, and the impairment in endothelial-mediated vasodilatation is attributed to increased oxidants that diminish NO bioactivity. In investigating the mechanisms involved, we found that independently of cyclic GMP, NO stimulates the uptake of cytosolic Ca²⁺ via the sarcoplasmic reticulum Ca²⁺ ATPase (SERCA), thereby relaxing vascular smooth muscle by lowering intracellular free Ca²⁺. Nitric oxide was found to do so by reacting with superoxide to form peroxynitrite, which in turn caused glutathione (GSH) to bind to SERCA cysteine thiols. Most of the GSH was bound to the most reactive thiol on SERCA cysteine-674, and mutation of this residue prevented stimulation of Ca²⁺ uptake by NO. In atherosclerotic arteries, we found that NO no longer stimulated SERCA activity because of the irreversible oxidation of the cysteine-674 thiol. These studies not only demonstrate a novel mechanism of NO-induced vasodilatation, but also provide an explanation as to how chronically increased levels of oxidants associated with disease impair vasodilatation in diseased arteries.