Effects of BmKNJX11, A Bioactive Polypeptide Purified from Buthus martensi Karsch, on Sodium Channels in Rat Dorsal Root Ganglion Neurons

Abstract

A long-chain polypeptide BmKNJX11 was purified from the venom of Asian scorpion Buthus martensi Karsch (BmK) by a combination of gel filtration, ion-exchange chromatography, and reverse-phase high-performance liquid chromatography. The molecular mass was found to be 7036.85 Da by electrospray ionization mass spectrometry. The first 15 N-terminal amino acid sequence of BmKNJX11 was determined to be GRDAY IADSE NCTYT by Edman degradation. With whole cell recording, BmKNJX11 inhibited tetrodotoxin-sensitive voltage-gated sodium channels (TTX-S VGSC) in freshly isolated rat dorsal root ganglion (DRG) neurons in a concentration- and voltage-dependent manner. At a concentration of 40 μg/ml BmKNJX11 lowered the activation threshold and produced negative shifting of TTX-S sodium current (I _Na) activation curve. In addition, BmKNJX11 induced shifting of the steady-state inactivation curve to the left, delayed the recovery of TTX-S I _Na from inactivation, and also reduced the fraction of available sodium channels. These results suggested that BmKNJX11 might exert effects on VGSC by binding to a specific site. Considering that TTX-S VGSC expressed in DRG neurons play a critical role in nociceptive transmission, the interaction of BmKNJX11 with TTX-S VGSC might lead to a change in excitability of nociceptive afferent fibers, which may be involved in the observed peripheral pain expression.

This study has been supported by the National Nature Science Foundation of China (30271137) and the Research Fund for the Doctoral Program of Higher Education (20060312001).