Objective:To investigate the influence of sufentanil on calcium-activated K+ channels (IKCa) in rat abdominal aortic smooth muscle cells,and to investigate its role in dilation of blood vessels.Methods: Rat abdominal aortic smooth muscle cells (AASMCs) were freshly obtained by enzymatic digestion.Whole-cell voltage-clamp technique was used to assess the effect of sufentanil (1×10-8,3×10-8,1×10-7mol/L ) on IKCa.Results: Sufentanil significantly increased the amplitude of IKCa compared with the control group (P<0.05 or P<0.01).The effect of sufentanil was reversible and in a concentration-dependent manner.Conclusion: Sufentanil can promote the activation of KCa channel in rat AASMCs,which might be related to the vasodilatory effect of sufentanil observed in clinical practice.