Abstract： Objective To study the role of neuronal nitric oxide synthase (nNOS) in ischemicpreconditioning and its mechanism in a cell model transiently exposed to COCl2 for mimicking ischemicpreconditioning. Methods SK-N-SH cells were pretreated with 300 μmol/L COCl2 for 3 h andcultured 24 h later in serum-free media to establish the cell model ofischemic preconditioning. 7-NI, aspecific inhibitor of nNOS, was used to explore the role ofnNOS in the preconditioning process. MTTassay and flow cytometry (FAM) were used to detect the cell proliferation and apoptosis, respectively, atdifferent time points after the preconditioning. Reverse transcriptase-polymerase chain reaction (RT-PCR)was performed to detect the expression levels of nNOS and the apoptosis-related genes after ischemicpreconditioning. Results In serum-flee culture after exposure to 300 μmol/L COCl2, the SK-N-SHcells showed an increase in cell proliferation by 2.5 folds and a reduction of the cell apoptotic rate by70%, with significant differences from the control cells (P<0.05). At 3 and 24 h after ischemicpreconditioning, the expression of nNOS and Bcl-2, an apoptosis suppressor gene, was up-regnlated andthe expression of Apaf-1, an apoptosis-promoting gene, was down-regnlated. These effects could bereversed by 7-NI, an inhibitor ofnNOS. Conclusion Pretreatment with 300 μmol/L COCl2 for 3 h canmimic ischemic preconditioning in SK-N-SH cells, in which process nNOS plays an important protectiverole by regulating the expression of Bcl-2 and Apaf-1.