Death of vascular smooth muscle cells (SMC) is an important cause of advanced atherosclerotic plaques rupture followed by thrombosis and sudden cardiac death. Although apoptosis has been shown to be a main cause of SMC death, the precise mechanisms are still poorly understood. cAMP signaling pathway plays an essential role in modulating the apoptotic response to different stress stimuli. Aside from the widely investigated G-protein-responsive transmembrane adenylyl cyclase, a second source of cellular cAMP, the ubiquitously expressed soluble adenylyl cyclase (sAC), has been demonstrated. However, the role of this cyclase in SMC apoptosis was unknown. To investigate this subject, apoptosis of rat aortic SMC was induced by oxidative stress, i.e. by treatment with 2,3- dimethoxy-1,4-naphthoquinone (DMNQ, 30 mM, 6 h) or H2O2 (300 mM, 6h). Apoptosis was analysed by TUNEL staining and caspase-3/-9 cleavage. Pharmacological inhibition of sAC with the selective inhibitor KH7 (ChemDiv) prevented oxidative stress-induced apoptosis, which was associated with a decrease in the cellular cAMP content. In contrast, treatment with inactive analogues of KH7, i.e. KH7.14, had no effect. Furthermore, inhibition of protein kinase A, an important cAMP target, with H89 or with adenosine 3',5'-cyclic monophosphorothioate demonstrated the anti-apoptotic effect. Analysis of the underlying mechanisms of the sAC- dependent apoptosis revealed activation of the mitochondrial pathway of apoptosis (cytochrome C release and caspase-9 cleavage), which was abolished by sAC inhibition. Taken together, these results suggest that sAC plays a significant role in the oxidative stress-induced mitochondrial apoptosis.