Blocking effect of Guan-Fu Base A on human Na V 1.5 channels and the
mutants expressed in Xenopus Laevis oocytes
Introduction GFA (Guan-Fu Base A) as one of the main active
substances in the Chinese medicine Ranunculaceae Aconite, has been
approved the effect of anti-atrial fibrillation via its atrial-selective
Na + channel-blocking action. It is recently
undergoing phase IV clinical study. However, the molecular mechanism of
Na V1.5 channel inhibition by GFA is largely unclear.
Methods and Results Na V1.5 channel and its
mutants were expressed in Xenopus oocytes and the currents were
recorded with two-microelectrode voltage-clamp. GFA inhibited Na
V1.5 currents in a concentration-dependent manner, with
IC 50 of 66.24 μM, 371.59 μM, and 381.08 μM for
wild type (WT), Delta KPQ (∆KPQ) and R1623Q constructs, respectively.
Both the mutations of ∆KPQ and R1623Q decreased inhibitory potency of
GFA about 5~6-fold. N406K mutation significantly altered
the inhibition effect of GFA. Even 1 mM GFA has almost no inhibitory
effect on the mutant. For both the WT and mutant channels, GFA reduced
the currents in concentration, voltage and time dependent manner.
Conclusion: GFA is a potent blocker of Na V1.5
channel. N406, the aromatic residues in the transmembrane helical of
DIS6, is most likely responsible for the high-affinity binding of GFA to
Na V1.5 channel.