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 mu mol/L) or SNP (100 mu mol/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 mu mol/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. (c) 2006 Elsevier Inc. All rights reserved.