AIM:To investigate the action of genistein(GST),abroad spectrum tyrosine kinase inhibitor,on voltage-gated potassium channels in guinea pig proximal colonsmooth muscle cells.METHODS:Smooth muscle cells in guinea pig proximalcolon were enzymatically isolated.Nystatin-perforatedwhole cell patch clamp technique was used to recordpotassium currents including fast transient outwardcurrent(I_(Kto))and delayed rectifier current(I_(Kdr)),two ofwhich were isolated pharmacologically with 10 mmol/Ltetraethylammonium or 5 mmol/L 4-aminopyridine.Contamination of calcium-dependent potassium currentswas minimized with no calcium and 0.2 mmol/L CdCl_2 inan external solution.RESULTS:GST(10-100μmol/L)reversibly and dose-dependently reduced the peak amplitude of I_(Kto)with anICso value of 22.0+6.9μmol/L.To a lesser extent,I_(Kdr)wasalso inhibited in both peak current and sustained current.GST could not totally block the outward potassiumcurrent as a fraction of the outWard potassium current,which was insensitive to GST.GST had no effect on thesteady-state activation(n=6)and inactivation kinetics(n=6)of I_(Kto).Sodium orthovanadate(1 mmol/L),apotent inhibitor of tyrosine phosphatase,significantlyinhibited GST-induced inhibition(P<0.05).CONCLUSION:GST can dose-dependently andreversibly block voltage-gated potassium channels inguinea pig proximal colon smooth muscle cells. AIM: To investigate the action of genistein (GST), abroad spectrum tyrosine kinase inhibitor, on voltage-gated potassium channels in guinea pig proximal colonsmooth muscle cells. METHODS: Smooth muscle cells in guinea pig proximalcolon were enzymatically isolated. Nystatin-perforatedwhole cell patch clamp technique was used to recordpotassium currents including fast transient outward current (I_ (Kto)) and delayed rectifier current (I_ (Kdr)), two of the wavelengths were isolated pharmacologicallyactive with 10 mmol / Ltetraethylammonium or 5 mmol / L 4- aminopyridine.Contamination of calcium -dependent potassium currents was minimized with no calcium and 0.2 mmol / L CdCl 2 inan external solution .RESULTS: GST (10-100 μmol / L) reversibly and dose- dependently reduced the peak amplitude of I_ (Kto) with an ICso value of 22.0 + 6.9 μmol /L.To a lesser extent, I_ (Kdr) wasalso inhibited in both peak current and sustained current. GST could not totally block the outward potassium current as a fraction of the outWard potassium current, which was insensitive to GST.GST had no effect on thesteady-state activation (n = 6) and inactivation kinetics (n = 6) of I_ (Kto) .Sodium orthovanadate (1 mmol / L), apotent inhibitor of tyrosine phosphatase, induced inhibition (P <0.05) .CONCLUSION: GST can dose-dependently andreversibly block voltage-gated potassium channels inguinea pig proximal colon smooth muscle cells.