PATHWAYS INVOLVED IN THE VASODILATATION INDUCED BY THE NEW NO DONOR.

FF07

Pereira,AC (1); Librand APL(2); da Silva, RS(2); Bendhack LM(1).

Laboratório de Farmacologia (1), Laboratório de Química (2), Depto. Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto – USP. Ribeirão Preto, SP- Brazil.

Introduction: Nitric oxide (NO) produced in the endothelial cells or released by NO donor migrates to vascular smooth muscle cells where it activates the soluble guanylyl-cyclase (sGC) that produces cGMP and activation of cGMP-dependent protein kinase (PKG). This enzyme can phosphorilate several proteins that could be involved in the vascular relaxation. Aim: This study aimed to investigate the pathways involved in the vasodilatation induced by the new NO donor cis-[Ru(bpy)₂(py)(NO)](PF₆)₃ (Py) sinthezised in our laboratory. Methods: Rats (180-200g) were killed and the thoracic aorta was removed. Vascular reactivity to this new NO donor was studied in denuded rat aortic rings pre-contracted with phenylephrine (Phe, 100nM) or 60mM KCl. Cumulative concentration-effect curves for the NO donor were constructed in the presence or in the absence of the selective guanylate cyclase (sGC) inhibitor (ODQ, 1µM), non-selective K⁺ channel blocker (TEA, 1mM), Cl^- channel blocker (NPPB, 10µM) and sarcoplasmic reticulum Ca⁺²-ATPase (SERCA) inhibitor (Tapsigargin, 1µM). Cumulative concentration-effect curves for CaCl₂ stimulated with 100nM Phe or 60mM KCl were constructed in the presence or in the absence of the NO donor (Py). We analysed the values of maximum effect (Emax) and the potency (pD₂) of the NO donor. Results: Py induced concentration-dependent relaxation in rat aorta pre-contracted with Phe (Emax: 105±1.08%; pD_2: 6.54±0.1; n=5) or KCl (Emax: 67.5±4.6%; pD_2: 5.79±0.11; n=5). However, the maximum effect (Emax) and potency (pD₂) values were lower KCl-contracted aorta. ODQ reduced the Emax (75±4.5%) and pD₂ (75±4.5%) in aortas pre-contracted with Phe. On the other hand, in KCl-contracted aortas, ODQ reduced the Emax (60.3±5.7%), but did not change pD₂ (5.29±0.09; n=8). TEA and NPPB did not alter the Emax (TEA: 98.6±2.1%, n=6; NPPB: 100.7±2.2%, n=7), but both reduced the potency (pD₂ ) of Py (TEA 5.85±0.1; n=6 and NPPB: 5.96±0.07, n=7). Interestingly, Tapsigargin reduced the Emax (82.1±4.6; n=5) and the potency of Py (5.82±0.21; n=5). The cumulative concentration-effect curves for CaCl₂ stimulated with 100nM Phe were similar to those stimulated with 60mM KCl (Phe Emax: 1.4±0.16%; pD₂: 0.47±0.19, n=9 and KCl Emax: 1.6±0.21%; pD₂:0.51±0.12, n=7). Incubation with the NO donor reduced the Emax of both curves (Phe: 0.1±0.06% and KCl: 0.7±0.11%). Conclusion: Taking together, our results show that the relaxation induced by the new NO donor involves the activation of sGC, K⁺ channels sensitive to TEA, Cl^- channels sensitive to NPPB and SERCA. Moreover, the NO donor in study almost abolished Ca²⁺ influx.