Effects of the venom of the Brazilian scorpion (Tityus serrulatus) on the compound action potential of the rabbit vagus nerve fibres.

1 The effects of the venom of the scorpion (Tityus serrulatus) on nerve fibres of the rabbit cervical vagus were studied by the single sucrose-gap technique. Scorpion venom (1 microgram/ml) increased irreversibly the duration of the B component of the compound action potential of the vagus nerves, leaving the C component with its normal configuration. Tetrodotoxin (200 nM) suppressed the prolongation of the action potential duration in venom-treated B fibres. 2 At the same concentration (1 microgram/ml), scorpion venom reduced the amplitude and the rate constant of decay of the hyperpolarization produced by tetanic stimulation of non-myelinated nerve fibres. 3 A lower concentration (0.2 micrograms/ml) blocked completely the hyperpolarization of the potassium-activated response. After washing, the potassium-activated response partially recovered its amplitude but there was a significant increase in the time constant of the decay of hyperpolarization. 4 It is suggested that scorpion venom may modify the sodium pumping mechanism within fibres as well as affecting the passive and active sodium permeability systems.