Objective:To investigate the effects and mechanisms of docosahexaenoie acid(DHA) with different concentrations on large conductance calcium-activated potassium channels (BK channels)in normal rat coronary smooth muscle cells (SMCs). Methods:Coronary SMCs were isolated by enzyme digestion. Effects of different concentrations of DHA on BK channels in absence and presence of cytochrome P450 (CYP) epoxygenase inhibitor SKF525A were studied by patch clamp in whole-cell configuration. Effects of DHA with different concentrations on BK single channels were studied by patch clamp in inside-out single channel configuration. Results:0.01-1.0 μmol/L(defined as low concentrations) of DHA activated whole-cell BK currents with a half effect concentration(EC50) of(0.24 ± 0.05)μmol/L. This effect could be abolished by pre-incubation with SKF525A. Concentration of 3-10 μmol/L (defined as high concentrations)of DHA activated whole-cell BK channels with an EC50 of(2.38 ± 0.22)μmol/L. However,this effect could not be abolished by pre-incubation with SKF525A. In the presence of 0,0.01,0.03,0.1,0.3,and 1 μmol/L DHA,the open probabilities of BK channels at 1 μmol/L calcium in external solution and test potentials at 60 mV were (0.095 2 ± 0.009 5),(0.093 9 ± 0.012 6),(0.098 6 ± 0.016 9),(0.099 5 ± 0.014 7),(0.097 5 ± 0.010 4),and(0.102 3 ± 0.020 6)respectively(P > 0.05,n=5). Low concentrations of DHA could not activate BK single channels. On the setting of 3 and 10 μmol/L DHA,the open probabilities of BK channels at 1 μmol/L calcium in external solution and test potentials at 60 mV were(0.700 3 ± 0.013 2),and(0.892 7 ± 0.053 2),respectively (P < 0.05,n=5). High concentrations of DHA could directly activate BK channels. Conclusion:BK channels can be activated by DHA in multiple mechanisms. Low concentration DHA can activate BK channel through CYP epoxygenase metabolites,while high concentration DHA can directly activate BK channel by binding to the channel proteins.