Roles for soluble guanylate cyclase and a thiol oxidation-elicited subunit dimerization of protein kinase G in pulmonary artery relaxation to hydrogen peroxide

We have previously provided evidence that hydrogen peroxide (H(2)O(2)) stimulates soluble guanylate cyclase (sGC) under conditions where it relaxes isolated endothelium-removed bovine pulmonary arteries (BPAs). Since it was recently reported that H(2)O(2) induces coronary vasorelaxation associated with a nitric oxide/cGMP-independent thiol oxidation/subunit dimerization-elicited activation of protein kinase G (PKG), we investigated whether this mechanism participates in the relaxation of BPAs to H(2)O(2). BPAs precontracted with serotonin (incubated under hypoxia to lower endogenous H(2)O(2)) were exposed to increasing concentrations of H(2)O(2). It was observed that 0.1-1 mM H(2)O(2) caused increased PKG dimerization and relaxation. These responses were associated with increased phosphorylation of vasodilator-stimulated phosphoprotein (VASP) at the serine-239 site known to be mediated by PKG. Treatment of BPAs with 1 mM DTT attenuated PKG dimerization, VASP phosphorylation, and relaxation to H(2)O(2). An organoid culture of BPAs for 48 h with 10 μM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a heme oxidant inhibitor of sGC activation, depleted sGC expression by 85%, associated with a 67% attenuation of VASP phosphorylation and 48% inhibition of relaxation elicited by 100 μM H(2)O(2). Thus both a sGC activation/cGMP-dependent and a thiol oxidation subunit dimerization/cGMP-independent activation of PKG appear to contribute to the relaxation of BPAs elicited by H(2)O(2).