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Ketamine blocks WT IhERG expressed in Xenopus oocytes in a concentration-dependent manner and predominantly interacts with the open hERG channels. The interaction of ketamine with hERG channel may involve the aromatic residues Tyr652 and Phe656.

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Aim: To investigate the blocking effects of methylflavonolamine (MFA) on human Na V 1.5 channels expressed in Xenopus laevis oocytes and on sodium currents (I Na ) in rabbit ventricular myocytes. Methods: Human Na V 1.5 channels were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique. I Na and action potentials in rabbit ventricular myocytes were studied using the whole-cell recording. Results: MFA and lidocaine inhibited human Na V 1.5 channels expressed in Xenopus oocytes in a positive rate-dependent and concentration-dependent manner, with IC 50 values of 72.61 μmol/L and 145.62 μmol/L, respectively. Both of them markedly shifted the steady-state activation curve of I Na toward more positive potentials, shifted the steady-state inactivation curve of I Na toward more negative potentials and postponed the recovery of the I Na inactivation state. In rabbit ventricular myocytes, MFA inhibited I Na with a shift in the steady-state inactivation curve toward more negative potentials, thereby postponing the recovery of the I Na inactivation state. This shift was in a positive rate-dependent manner. Under current-clamp mode, MAF significantly decreased action potential amplitude (APA) and maximal depolarization velocity (V max ) and shortened action potential duration (APD), but did not alter the resting membrane potential (RMP). The demonstrated that the kinetics of sodium channel blockage by MFA resemble those of class I antiarrhythmic agents such as lidocaine. Conclusion: MFA protects the heart against arrhythmias by its blocking effect on sodium channels.