The effects of ATP-sensitive mitochondrial K+ channel (mitoK(ATP)) on mitochondrial membrane potential (Delta psi m), cell proliferation and protein kinase C alpha (PKC alpha) expression in airway smooth muscle cells (ASMCs) were investigated. Thirty-six Sprague-Dawley (SD) rats were immunized with saline (controls) or ovalbumin (OVA) with alum (asthma models). ASMCs were cultured from the lung of control and asthma rats. ASMCs were treated with diazoxide (the potent activator of mitoK(ATP)) or 5-hydroxydencanote (5-HD, the inhibitor of mitoK(ATP)). Rhodamine-123 (R-123) was used to detect Delta psi m. The expression of PKC alpha protein was examined by using Western blotting, while PKC alpha mRNA expression was detected by using real-time PCR. The proliferation of ASMCs was measured by MTT assay and cell cycle analysis. In diazoxide-treated normal ASMCs, the R-123 fluorescence intensity, protein and mRNA levels of PKC alpha, MTT A values and percentage of cells in S phase were markedly increased as compared with untreated controls. The ratio of G(0)/G(1) cells was decreased (P < 0.05) in diazoxide-treated ASMCs from normal rats. However, there were no significant differences between the ASMCs from healthy rats treated with 5-HD and the normal control group. In untreated and diazoxide-treated ASMCs of asthmatic rats, the R-123 fluorescence intensity, protein and mRNA levels of PKC alpha, MTT A values and the percentage of cells in S phase were increased in comparison to the normal control group. Furthermore, in comparison to ASMCs from asthmatic rats, these values were considerably increased in asthmatic group treated with diazoxide (P < 0.05). After exposure to 5-HD for 24 h, these values were decreased as compared with asthma control group (P < 0.05). In ASMCs of asthma, the signal transduction pathway of PKC alpha may be involved in cell proliferation, which is induced by the opening of mitoK(ATP) and the depolarization of Delta psi m.