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 d isplay a biphasic inhibitory effect on the C component of the rat nocicepti ve flexion reflex by subcutaneous injection in vivo, and also on the total Na+ currents of rat dorsal root ganglion neurons using whole-cell patch cla mping. 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 N a+ currents, brought about by 0.01 mug/mul BmK IT2, reversed less rapidly a nd completely than the partial block of the tetrodotoxin-sensitive (TTX-S) current brought about by the same concentration of BmK IT2. These results s uggest that the inhibition of the rat nociceptive flexion reflex by BmK 1T2 may be attributed to modulation of the different voltage-gated Na+ channel s. (C) 2001 Elsevier Science Ltd. All rights reserved.