Abstract: The effects of berberine on potassium subtypes were investigated by usingpatch-clamp whole cell recording techniques.Berberine is known to be effective in lowering bloodglucose and ameliorating arrhythmia. Our results indicate that , berberine can prolong action potentialduration(APD),decrease l_k1 and outward I_tail,but showed no effcet on I_k. In addition ,berberinewas also shown to antagonize cromakalim(BRL-34915)induced inhibition of APD and the increase of K_ATP. These suggest that berberine ean inhibit voltage-dependent and ATP-sensitive potassiumchannels. It appears that the mechanisms of antiarrhythmic and antidiabetic action of berberine mightbe due to its potassium channel blocking effects.