BOT IT2, A TOXIN PARALYTIC TO INSECTS FROM THE BUTHUS-OCCITANUS-TUNETANUS VENOM MODIFYING THE ACTIVITY OF INSECT SODIUM-CHANNELS

The effects of insect toxin Bot IT2, purified from the venom of the sc orpion Buthus occitanus tunetanus, were investigated on the isolated g iant axon and on isolated dorsal unpaired median (DUM) neurone of the cockroach Periplaneta americana under current- and voltage-clamp condi tions, using the double-oil-gap technique and the patch-clamp techniqu e, respectively. In both preparations, Bot IT2 induces a limited depol arization together with the development of a repetitive activity in ax on and an increase of spontaneous discharge frequency in DUM neurone. After artificial hyperpolarization to the normal resting level, platea u potentials can be evoked in both preparations. Under voltage-clamp c onditions, Bot IT2 induces a similar effect in axon and DUM neurone by acting specifically on sodium channels. The peak sodium current is de creased and simultaneously a new current with very slow activation-dea ctivation kinetics is developed. Voltage dependence of this slow curre nt is not very different from that of the control. The inactivation of the fast component is incomplete because it is masked by the developm ent of the slow component. These results suggest that Bot IT2 modifies the kinetics of insect sodium channel activation, and the transformat ion of normal fast channels into slow ones is discussed.