The sulphonylurea glibenclamide inhibits voltage dependent potassium currents in human atrial and ventricular myocytes

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Abstract
1 It was the aim of our study to investigate the effects of the sulphonylurea glibenclamide on voltage dependent potassium currents in human atrial myocytes. 2 The drug blocked a fraction of the quasi steady state current (ramp response) which was activated positive to -20 mV, was sensitive to 4-aminopyridine (500 microM) and was different from the ATP dependent potassium current IK(ATP). 3 Glibenclamide dose dependently inhibited both, the peak as well as the late current elicited by step depolarization positive to -20 mV. The IC50 for reduction in charge area of total outward current was 76 microM. 4 The double-exponential inactivation time-course of the total outward current was accelerated in the presence of glibenclamide with a tau(fast) of 12.7+/-1.5 ms and a tau(slow) of 213+/-25 ms in control and 5.8+/-1.9 ms (P<0.001) and 101+/-20 ms (P<0.05) under glibenclamide (100 microM). 5 Our data suggest, that both repolarizing currents in human atrial myocytes, the transient outward current (Ito1) and the ultrarapid delayed rectifier current (IKur) were inhibited by glibenclamide. 6 In human ventricular myocytes glibenclamide inhibited Ito1 without affecting the late current. 7 Our data suggest that glibenclamide inhibits human voltage dependent cardiac potassium currents at concentrations above 10 microM.