Nitric oxide generated by the compound RuBPY promotes the vascular smooth cell membrane hyperpolarization

The cis-[Ru(bpy)(2)(py)NO2](PF6) specie (RuBPY) has been used as nitric oxide (NO) delivery agent. It is an NO reservoir and it is thermodynamically stable in aqueous solution. This study aimed to evaluate the NO specie generated by RuBPY as compared to NO released from sodium nitroprusside (SNP) and to study the cellular mechanisms specially focusing the activation of soluble guanylyl-cyclase (sGC), K+ channels and the cell membrane hyperpolarization, which are the main targets for NO-inducing vascular relaxation. NO generated by RuBPY and the vascular smooth muscle cell (VSMC) membrane potential were measured by confocal microscopy. The cellular mechanisms of aorta relaxation were investigated using K+ channel blockers and sGC inhibitor. NO released from RuBPY was higher than NO released from SNP. RuBPY released only radicalar NO0 and SNP released both NO- and NO0. The concentration-effect curves for RuBPY-induced relaxation was shifted to the right by inhibition of sGC with ODQ and by the non-selective blockade of K+ channels with TEA. The simultaneous combination of ODQ and TEA abolished the vasorelaxation induced by RuBPY. The membrane potential measured by the sensitive dye 4-Di-ANNEPS demonstrated that RuBPY induces cell membrane hyperpolarization. Taken together, our results indicate that the large amount of NO0 specie generated by RuBPY induces vasorelaxation due to activation of sGC, K+ channels sensitive to TEA, and cell membrane hyperpolarization. These results indicate that NO0 generated from RuBPY can also directly activate the K+ channels in an independent way of sGC. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.