The impact of experimental variables in twitch tension recording on triphasic action of phospholipase A2 neurotoxins at the neuromuscular junction and acetylcholine release.

Electrophysiological investigations have previously demonstrated that snake venom phospholipase A2 (PLA2) neurotoxins such as β-bungarotoxin (BuTx), taipoxin, notexin, crotoxin, and ammodytoxin (Amtx), exert a triphasic effect on the release of acetylcholine (ACh) at the neuromuscular junction (NMJ). The first phase is characterized by a transient decrease in twitch height, which is followed by a facilitatory phase during which twitch height exceeds control levels. The final phase is a reduction of twitch height, ultimately leading to paralysis. The manifestation of this triphasic effect occurs under specific experimental conditions. This study aims to investigate these "specific conditions" and how various experimental variables can influence the twitch tension recordings and their effect on the modulation of the triphasic action of the aforementioned PLA2 neurotoxins at the NMJ, and their impact on ACh release. These variables include factors such as the concentration of Mg2+ and Ca2+, temperature, stimulation frequency, toxin concentration, washout procedures, interactions between toxins, animal weight, and the presence of 3,4-diaminopyridine (3,4-DAP) and tetraethylammonium (TEA). In conclusion, this research highlights that the triphasic action of PLA2 neurotoxins at the NMJ is not a fixed phenomenon but can be substantially modulated by changes in experimental conditions. These findings emphasize the importance of carefully considering experimental parameters when studying the effects of PLA2 neurotoxins. Variations in conditions may influence responses and impact the interpretation of underlying neurotoxic mechanisms.