Inhibition of $\beta $-bungarotoxin Action by Bee Venom Phospholipase A$_{2}$

$\beta $-Bungarotoxin ($\beta $-BuTX) induces twitching of innervated frog muscle and subsequently blocks transmitter release from motor nerve endings. These actions of $\beta $-BuTX are prevented if the nerve-muscle junctions are pretreated with a low concentration of phospholipase A$_{2}$ from bee venom. When the Ca$^{2+}$ in the external fluid is replaced by Sr$^{2+}$, the phospholipase activity of $\beta $-BuTX is negligible and, in these conditions, $\beta $-BuTX causes a decrease in the amplitude of endplate potentials but does not go on to block transmitter release completely.