The balance between apoptosis and proliferation in pulmonary artery smooth muscle cells (PASMCs) is important in maintaining normal pulmonary vascular structure. Activity of voltage-gated K+ (KV) channels has been demonstrated to regulate cell apoptosis and proliferation. Treatment of PASMCs with staurosporine (ST) induced apoptosis in PASMCs, augmented KV current [IK(V)], and induced mitochondrial membrane depolarization. High K+ (40 mM) negligibly affected the ST-induced mitochondrial membrane depolarization but inhibited the ST-induced IK(V) increase and apoptosis. Blockade of KV channels with 4-aminopyridine diminished IK(V) and markedly decreased the ST-mediated apoptosis. Furthermore, the ST-induced apoptosis was preceded by the increase in IK(V). These results indicate that ST induces PASMC apoptosis by activation of plasmalemmal KV channels and mitochondrial membrane depolarization. The increased IK(V) would result in an apoptotic volume decrease due to a loss of cytosolic K+ and induce apoptosis. The mitochondrial membrane depolarization would cause cytochrome c release, activate the cytosolic caspases, and induce apoptosis. Inhibition of KV channels would thus attenuate PASMC apoptosis.