Characterization of the mechanisms of action and nitric oxide species involved in the relaxation induced by the ruthenium complex

Nitric oxide (NO) plays an important role in the control of vascular tone. NO donors have therapeutic use and the most used NO donors, nitroglycerin and sodium nitroprusside have problems in their use. Thus, new NO donors have been synthesized to minimize these undesirable effects. Nytrosil ruthenium complexes have been studied as a new class of NO donors. trans-[RuCl([15]aneN4)NO]2+, induces vasorelaxation only in presence of reducing agent. In this study, we characterized the mechanisms of vasorelaxation of trans-[RuCl([15]aneN4)NO]2+ in denuded rat aorta and identified which NO forms are involved in this relaxation. We also evaluated the effect of this NO donor in decreasing the cytosolic Ca2+ concentration ([Ca2+]c) of the vascular smooth muscle cells. Vasorelaxation to trans-[RuCl([15]aneN4)NO]2+ (Emax: 101.8. ± 2.3%, pEC50: 5.03. ± 0.15) was almost abolished in the presence of the NO
• scavenger hydroxocobalamin (Emax: 4.0. ± 0.4%; P < 0.001) and it was partially inhibited by the NO− scavenger l-cysteine (Emax: 79.9. ± 6.9%, pEC50: 4.41. ± 0.06; P < 0.05). The guanylyl cyclase inhibitor ODQ reduced the Emax (57.7 ± 4.0%, P < 0.001) and pEC50 (4.21. ± 0.42, P < 0.01) and the combination of ODQ and TEA abolished the response to trans-[RuCl([15]aneN4)NO]2+. The blockade of voltage-dependent (Kv), ATP-sensitive (KATP), and Ca2+-activated (KCa) K+ channels reduced the vasorelaxation induced by trans-[RuCl([15]aneN4)NO]2+. This compound significantly reduced [Ca2+]c (from 100% to 85.9. ± 3.5%, n = 4). In conclusion, our data demonstrate that this NO donor induces vascular relaxation involving NO
• and NO− species, that is associated to a decrease in [Ca2+]c. The mechanisms of vasorelaxation involve guanylyl cyclase activation, cGMP production and K+ channels activation.