Involvement of batrachotoxin binding sites in ginsenoside-mediated voltage-gated Na+ channel regulation

Recently, we showed that the 20(S)-ginsenoside Rg(3) (Rg(3)), an active ingredient of Panax ginseng, inhibits rat brain Na(v)1.2 channel peak currents (I-Na). Batrachotoxin (BTX) is a steroidal alkaloid neurotoxin and activates Na-v channels through interacting with transmembrane domain-I-segment 6 (IS6) of channels. Recent report shows that ginsenoside inhibits BTX binding in rat brain membrane fractions. However, it needs to be confirmed whether biochemical mechanism is relevant physiologically and which residues of the BTX binding sites are important for ginsenoside regulations. Here, we demonstrate that mutations of BTX binding sites such as N418K and L421K of rat brain Na(v)1.2 and L437K of mouse skeletal muscle Na(v)1.4 channel reduce or abolish Rg(3) inhibition of I-Na and attenuate Rg(3)-mediated depolarizing shift of the activation voltage and use-dependent inhibition. These results indicate that BTX binding sites play an important role in modifying Rg(3)-mediated Na+ channel properties. (c) 2008 Elsevier B.V. All rights reserved.