Differentiation of L- and D-S-Nitrosothiol Recognition Sites In Vivo

Abstract

The main aim of this study was to determine the effects of the lipophobic electron acceptor, nitroblue tetrazolium (NBT), on the vasodilator responses elicited by femoral vein injections of L- and D-S-nitrosocysteine (L- and D-SNC), L- and D-S-nitroso-beta,beta-dimethylcysteine (L- and D-SNPEN) and the nitric oxide (NO) donor, MAHMA NONOate, in pentobarbital-anesthetized rats. L- and D-SNC, L- and D-SNPEN, and MAHMA NONOate elicited dose-dependent falls in mean arterial blood pressure (MAP), and hindquarter (HQR), renal (RR), and mesenteric (MR) vascular resistances. The L-SNC- and L-SNPEN-induced depressor and vasodilator responses were markedly attenuated after injection of NBT. The D-SNC- and D-SNPEN-induced falls in mean arterial pressure, hindquarter, and mesenteric vascular resistances were also reduced after injection of nitroblue tetrazolium whereas the falls in renal resistances were not affected. However, nitroblue tetrazolium inhibited the L-SNC and L-SNPEN responses much more profoundly than the D-SNC and D-SNPEN responses in each vascular bed. In contrast, the MAHMA NONOate-induced responses were not attenuated by nitroblue tetrazolium. This study demonstrates that nitroblue tetrazolium attenuates L- and D-SNC-and L- and D-SNPEN- mediated but not NO-mediated vasodilation. The lack of effects of NBT on the NO responses suggests that NBT does not interfere with the intracellular mechanisms by which NO relaxes vascular smooth muscle. The more pronounced effects of NBT on the vasodilator effects of L-SNC and L-SNPEN than D-SNC and D-SNPEN suggests that these stereoisomers differentially interact with stereoselective S-nitrosothiol recognition sites in the vasculature and that these sites (or their signaling elements) contain thiol residues that may be susceptible to occupation and/or oxidation (ie, disulfide-bond formation) by nitroblue tetrazolium.

Light-induced vs. bradykinin-induced relaxation of coronary arteries: do S-nitrosothiols act as endothelium-derived hyperpolarizing factors?

“…This process occurs in a stereoselective manner [15,16,21] and leads, among others, to activation of Ca 2þ -dependent K þ channels [11,36]. Indeed, L-S-nitrosocysteine (L-SNC), but not D-S-nitrosocysteine, activated endothelial IK Ca and SK Ca in PCAs [10], thus causing K þ accumulation in the myoendothelial space and subsequent vasorelaxation.…”

“…Storage sites for S-nitrosothiols have been proposed to exist in endothelial cells [9,10,[13][14][15][16]. Interestingly, in this regard, light-induced vasorelaxation ('photorelaxation' [17]) is also mediated via S-nitrosothiols [18][19][20].…”

“…Light induces the decomposition of S-nitrosothiols by homolytic cleavage of the sulfur nitrogen bond to yield a disulfide and nitric oxide. Thus, S-nitrosothiols may exert effects either directly, via binding to S-nitrosothiol recognition sites [16,21], or indirectly, through the generation of nitric oxide and the subsequent guanylyl cyclase activation and guanosine-3 0 ,5 0 -cyclic monophosphate (cGMP) formation in smooth muscle cells [22,23]. Rodriguez et al [24] have demonstrated that nitrite also shows photoactivity, though at two orders of magnitude lower than that of S-nitrosothiols.…”

Local and systemic vasodilatory effects of low molecular weight S-nitrosothiols

“…In the cGMP-dependent pathway, SNOs are thought to enter the cell via the L-type amino acid transporter (LAT)[7–9], where they then release the NO moiety to activate soluble guanylate cyclase (sGC)[10–12]. Proposed cGMP-independent pathways to vasodilation may involve the S-transnitrosylation of functional proteins in the contractile signaling pathways[3, 4, 13, 14]. …”

“…Previous studies comparing the hemodynamic effects of different SNOs were performed by intravenous administration of the SNOs[3, 4, 13]. However, SNOs injected into the circulation will confront either rapid enzymatic conversion to other species or S-transnitrosylation reactions with plasma thiols that may transfer the NO moiety to a molecule with distinctly different membrane permeability and bioactivity[17].…”