The muscarinic agonist carbamylcholine stimulated 5-fold 86Rb efflux from preloaded rat parotid acini. Apamin was without effect on this carbamylcholine-induced 86Rb efflux. By contrast, the venom from Leiurus quinquestriatus (a scorpion from Israel) inhibited non-competitively this efflux while being without effect on the carbamylcholine-stimulated 45Ca efflux and amylase release. This heat-resistant inhibitory effect of the venom was destroyed by boiling in the presence of dithiothreitol. These results suggest that the venom from L. quinquestriatus contains a toxin capable to block apamin-insensitive calcium-activated potassium channels in rat parotid acini.
