Peroxynitrite Effects on Smooth Muscle Contractility

Abstract

<p> Peroxynitrite is formed in blood vessels upon reaction of superoxide anion with nitric oxide (NO). It can oxidize proteins and thiols and nitrosylate free or protein bound thiols and tyrosine residues, thereby producing vascular dysfunction. Peroxynitrite therefore, may contribute to hypertension and cardiovascular diseases. We investigated the in vitro effects of commercially available peroxynitrite. De-endothelialized rings from the left descending coronary artery of pig were treated with peroxynitrite for 30 min, washed and then contracted with cyclopiazonic acid (CPA) or by membrane depolarization with KCl. Tissues pre-treated with peroxynitrite showed inhibition of the CPA-induced contraction with an IC50 of ≈100 uM but there was no effect on KCl-induced contraction. Peroxynitrite is stable only at alkaline pH and it may decompose to form superoxide and NO. However, including superoxide dismutase + catalase along with peroxynitrite did not change its effect.</p> <p> Next, we used the same protocol to compare the effects of peroxynitrite and NO generating agents: 3-morpholino sydnonimine (SIN-1), s-nitroso-N-acetylpenicilliamine (SNAP), sodium nitroprusside (SNP) and spermine nonoate. The effectiveness of these agents to inhibit the CPA-induced contraction was SNAP > spermine nonoate ≥ SIN-1 > SNP. SNAP was the most effective in inhibiting the KCl-induced contraction with spermine nononoate being less effective and SIN-1 and SNP not producing any significant inhibition. We further investigated the effect of SNAP. Catalase, superoxide dismutase or CPTIO (a NO scavenger) did not prevent the effects of SNAP on the KCl or the CPA-induced contractions. The guanylate cyclase inhibitor ODQ, partially reversed the effects of only low concentrations of SNAP. Thus, pretreatment with NO generating agents such as SNAP and spermine NONOate appear to be more effective in inhibiting the contraction of the pig coronary artery than with peroxynitrite or the peroxynitrite generating agent SIN-1. Since SIN-1, SNAP, SNP and NONOates produce different amounts of peroxynitrite, nitric oxide and S-nitrosylation products, their effects may be used to delineate the molecular basis of the actions of peroxynitrite and NO on the arterial function.</p>