Effect of toxins isolated from the venom of the scorpionCentruroides sculpturatus on the Na currents of the node of ranvier

Abstract

1. The effect of various toxin fractions isolated by Watt et al. (1978) from the venom of the scorpion Centruroides sculpturatus Ewing on the Na currents of the node of Ranvier has been studied with the voltage clamp method. 2. The toxin fractions were applied externally. The most potent fractions were toxins III, IV and V which were effective in concentrations of 0.33-3.33 microgram/ml. The effect of toxins III and IV was quite different from that of toxin V. 3. In toxin III or IV - treated nodes a strong depolarizing pulse was followed by a transient shift of the negative resistance branch of the INa (E) curve to more negative potentials. The amount of shift varied between -10 and -60 mV. A 500 ms depolarizing pulse of small amplitude produced a slowly developing Na inward current which slowly decayed after the end of the pulse. Inactivation was incomplete, even with 500 ms pulses to 0 mV. 4. The transient shift of the INa (E) curve was not seen in nodes treated with toxin V. This toxin merely caused slow and incomplete Na inactivation. The effect of toxin IV was not suppressed by a four times higher concentration of toxin V, suggesting that the two toxins act on different receptors. 5. Toxin I acted like toxin IV but was about 10 times less potent. The effect of high concentrations of variants 1, 2, 3, 5, 6 resembled tha of toxin V. 6. All effects observed with toxin III or IV were also seen with the whole venom (cf. Cahalan 1975).

Resurgent Current and Voltage Sensor Trapping Enhanced Activation by a β-Scorpion Toxin Solely in Nav1.6 Channel

“…4). To some extent, these studies explained previous observations of scorpion venom actions (7) and the effects of ␤-scorpion toxins on frog and toad Ranvier nodes (8,9). In contrast, sea anemone toxins and ␣-scorpion toxins disrupt the inactivation process by interacting with the extracellular IVS3-S4 loop (3).…”

Structure and Function of the Voltage Sensor of Sodium Channels Probed by a β-Scorpion Toxin

“…Binding of toxins to IVS3-S4 is thought to slow inactivation by preventing the normal outward movement of the IVS4 transmembrane segment during channel gating (23,26). In contrast to these toxins that inhibit inactivation gating, ␤-scorpion toxins bind to neurotoxin receptor site 4 on sodium channels and enhance activation by shifting its voltage dependence to more negative potentials (27)(28)(29)(30)(31)(32)(33)(34). Our previous results (34) implicate the extracellular loops S1-S2 and S3-S4 in domain II in formation of neurotoxin receptor site 4.…”

Purification and characterization of a β‐toxin from the venom of the African scorpion Leiurus quinquestriatus

“…The toxin-containing stock solution was prepared with an appropriate NaCl-deficient Ringer. Membrane currents were recorded on a computer and corrected for capacitative and leakage currents as described in [4,11,12].…”

“…The venom of the North American species Centruroides sculpturatus acts quite differently [2]. Among the toxins isolated from this venom [3], only toxin V causes a drastic inhibition of inactivation [4], while toxins I, III, IV, VI and VII of C. sculpturatus produce a transient shift of Na activation to more negative potentials [5].…”