1 BAY 41-8543 is a novel, highly speci®c and so far the most potent NO-independent stimulator of sGC. Here we report the eects of BAY 41-8543 on the isolated enzyme, endothelial cells, platelets, isolated vessels and Langendor heart preparation. 2 BAY 41-8543 stimulates the recombinant sGC concentration-dependently from 0.0001 mM to 100 mM up to 92-fold. In combination, BAY 41-8543 and NO have synergistic eects over a wide range of concentrations. Similar results are shown in implying that BAY 41-8543 stimulates the sGC directly and furthermore makes the enzyme more sensitive to its endogenous activator NO. 3 In vitro, BAY 41-8543 is a potent relaxing agent of aortas, saphenous arteries, coronary arteries and veins with IC 50 -values in the nM range. 4 In the rat heart Langendor preparation, BAY 41-8543 potently reduces coronary perfusion pressure from 10 79 to 10 76 g ml 71 without any eect on left ventricular pressure and heart rate. 5 BAY 41-8543 is eective even under nitrate tolerance conditions proved by the same vasorelaxing eect on aortic rings taken either from normal or nitrate-tolerant rats. 6 BAY 41-8543 is a potent inhibitor of collagen-mediated aggregation in washed human platelets (IC 50 =0.09 mM). In plasma, BAY 41-8543 inhibits collagen-mediated aggregation better than ADPinduced aggregation, but has no eect on the thrombin pathway. BAY 41-8543 is also a potent direct stimulator of the cyclic GMP/PKG/VASP pathway in platelets and synergizes with NO over a wide range of concentrations. 7 These results suggest that BAY 41-8543 is on the one hand an invaluable tool for studying sGC signaling in vitro and on the other hand its unique pro®le may oer a novel approach for treating cardiovascular diseases.
IntroductionGuanylyl cyclases (GTP pyrophosphate-lyase [cyclizing]; EC 4.6.1.2) catalyse the biosynthesis of cyclic GMP from GTP. While the membrane bound forms are monomers which are stimulated by the natriuretic peptides, the soluble guanylyl cyclases exist as heterodimers consisting of an a-and a bsubunit and contain a heme as a prosthetic group (Wedel & Garbers, 1997). By formation of cyclic GMP as a second messenger, sGC plays an important role in smooth muscle cell relaxation (Lincoln, 1989), inhibition of platelet aggregation, retinal signal transduction (Moncada & Higgs, 1995) and synaptic transmission (Zhuo & Hawkins, 1995). The sGC is the intracellular receptor for the ubiquitous biological messenger NO (Moncada et al., 1991;Furchgott, 1999;Murad, 1999;Ignarro, 1999) and is also activated by the benzylindazole derivative YC-1 (Ko et al., 1994; MuÈ lsch et al., 1997;Friebe et al., 1996;Hoenicka et al., 1999). In several studies, YC-1 was shown to inhibit platelet aggregation by elevation of cyclic GMP causing VASP phosphorylation (Wu et al., 1995;1997;Ko et al., 1994;Friebe et al., 1998;Becker et al., 2000) and to relax precontracted aortic rings (MuÈ lsch et al., 1997). Interestingly, in addition to the direct activation of the puri®ed sGC by YC-1, an overadditive eect was observed by the c...