The inhibitory effects of BmK IT2, a scorpion neurotoxin on rat nociceptive flexion reflex and a possible mechanism for modulating voltage-gated Na(+) channels.

Buthus martensi Karsch IT2 (BmK IT2), a scorpion neurotoxin, was found to display a biphasic inhibitory effect on the C component of the rat nociceptive flexion reflex by subcutaneous injection in vivo, and also on the total Na(+) currents of rat dorsal root ganglion neurons using whole-cell patch clamping. BmK IT2 blocked the tetrodotoxin-resistant (TTX-R) component of the Na(+) currents with a degree of selectivity. The partial block of the TTX-R Na(+) currents, brought about by 0.01 microg/microl BmK IT2, reversed less rapidly and completely than the partial block of the tetrodotoxin-sensitive (TTX-S) current brought about by the same concentration of BmK IT2. These results suggest that the inhibition of the rat nociceptive flexion reflex by BmK IT2 may be attributed to modulation of the different voltage-gated Na(+) channels.