Voltage-gated Na+ (NaV) channels are significant therapeutic targets for the treatment of cardiac and
neurological disorders, thus promoting the search for novel NaV channel
ligands. With the objective of discovering new blockers of NaV channel
ligands, we screened an In-House vegetal
alkaloid library using fluorescence cell-based assays. We screened 62
isoquinoline alkaloids (IA) for their ability to decrease the FRET signal of voltage sensor probes (VSP), which were induced by the activation of NaV channels with batrachotoxin (BTX) in GH3b6 cells. This led to the selection of five IA:
liriodenine, oxostephanine, thalmiculine,
protopine, and
bebeerine, inhibiting the BTX-induced VSP signal with micromolar IC50. These five
alkaloids were then assayed using the Na+
fluorescent probe ANG-2 and the patch-clamp technique. Only oxostephanine and
liriodenine were able to inhibit the BTX-induced ANG-2 signal in HEK293-hNaV1.3 cells. Indeed,
liriodenine and oxostephanine decreased the effects of BTX on Na+ currents elicited by the hNaV1.3 channel, suggesting that conformation change induced by BTX binding could induce a bias in fluorescent assays. However, among the five IA selected in the VSP assay, only
bebeerine exhibited strong inhibitory effects against Na+ currents elicited by the hNav1.2 and hNav1.6 channels, with IC50 values below 10 µM. So far,
bebeerine is the first BBIQ to have been reported to block NaV channels, with promising therapeutical applications.