Interaction Between Corticosteroids and Presynaptic-Acting Toxins from Snake Venoms in Rat Phrenic Nerve Terminals

Corticosteroids and the toxins beta-Bungarotoxin (beta-BuTx) and the angusticeps-type “F7”-toxin from snake venoms all affect neuromuscular transmission at the presynaptic site of the motor- endplate in rodent nerve-muscle preparations (1,2). Prednisolone and dexamethasone (Dex), in low concentrations, increase the amplitude of the miniature endplate potentials (MEPPs) without affecting the rate of transmitter release (3). On the other hand beta-BuTx causes, after an initial decrease followed by an increase of MEPP frequency, failure of transmitter release (4). The polypeptide “F7” one of the components of the venom of the green mamba, Dendroaspis angusticeps, augments acetylcholine release (5). These effects of the corticosteroids, beta-BuTx and “F7” toxin on acetylcholine release only occur after a latent period of 30 to 60 min, suggesting that in each case an indirect mechanism is involved.