Objective To evaluate the role of large conductance calcium-activated potassium (BKCa) channels in vascular hyporesponsiveness in rats with obstructive jaundice.Methods Eighteen male Sprague-Dawley rats,weighing 180-200 g,were randomly divided into 3 groups (n =6 each) using a random number table:control group (group C),sham operation group (group S),and bile duct ligation group (group BDL).Obstructive jaundice was produced by common bile duct ligation.At 7 days after surgery,blood samples were collected for determination of the levels of serum total bilirubin (TBL),direct bilirubin (DBL),indirect bilirubin (IBL),alanine aminotransferase (ALT),and aspartate aminotransferase (AST).Thoracic aortic rings were prepared,and the endothelium was removed.The aortic rings were sequentially perfused with different concentrations of norepinephrine (NE) and sodium nitroprusside (SNP),and the maximum amplitude of contraction and dilatation of aortic rings was recorded.The aortic rings were then perfused with BKCa channel blocker Chtx with the final concentration of 10 7 mol/L,followed by perfusion with different concentrations of NE and SNP again,and the maximum amplitude of contraction and dilatation of aortic rings was recorded under each concentration.The percentage of maximum contraction and dilatation (maximum amplitude after Chtx administration÷maximum amplitude before Chtx administration× 100％) was calculated.Results Compared with C and S groups,the levels of TBL,DBL,IBL,ALT and AST in serum were significantly increased,the maximum amplitude of NE-induced contraction of aortic rings was decreased,and the percentage of the maximum NE-induced dilatation of aortic rings was increased,the maximum amplitude of SNP-induced contraction of aortic rings was increased,and the percentage of the maximum SNP-induced dilatation of aortic rings was decreased in group BDL.Conclusion Excessivc opening of BKCa channels may be involved in the mechanism of vascular hyporesponsiveness in rats with obstructive jaundice.