Cytosolic calcium concentration is reduced by photolysis of a nitrosyl ruthenium complex in vascular smooth muscle cells

The effect of the NO donors cis-[RuCl(bpy)2(NO)](PF6) (RUNOCL) and sodium nitroprusside (SNP) on the cytosolic Ca2+ concentration ([Ca2+]c) was studied in cells isolated from the rat aorta smooth muscle of cells isolated from the rat aorta smooth muscle. SNP is a metal nitrosyl complex made up of iron, cyanide groups, and a nitro moiety; the RUNOCL complex is made up of ruthenium and bipyridine ligands, with chloride and nitrosyl groups in the ruthenium axial positions. Rat aorta smooth muscle cells were loaded with fluo-3 acetoxymethyl ester (Fluo-3 AM) and imaged by a confocal scanning laser microscope excited with the 488 nm line of the argon ion laser. Fluorescence emission was measured at 510 nm. One of the NO donors, RUNOCL (100 μmol/L) or SNP (100 μmol/L), was then added to the cell chamber and the fluorescent intensity percentage (%IF) was measured after 240 s. RUNOCL reduced the %IF to 60.0 ± 10.0% of the initial value. After treatment with the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) (10 μmol/L), the measurement of %IF was 81.0 ± 5.0% (n = 4). In the presence of tetraethylammonium (TEA) (1 mmol/L) the %IF was 79.0 ± 6.4% (n = 4). A combination of ODQ and TEA increased the %IF to 97.0 ± 3.5% (n = 4). As for SNP, it reduced the %IF to 81.4 ± 4.7% (n = 4), but this effect was inhibited by ODQ (%IF 94.0 ± 3.6%; n = 4) and TEA (%IF 88.0 ± 2.1%; n = 4). The combination of ODQ and TEA increased (%IF 92.0 ± 2.8%; n = 4). Taken together, these results indicate that both the new NO donor RUNOCL and SNP reduce [Ca2+]c. Our data also give evidence that soluble guanylyl cyclase and K+ channels sensitive to TEA are involved in the mechanisms responsible for the reduction in [Ca2+]c of the rat aorta smooth muscle cells.