Actions of Androctonus australis and Leiurus quinquestriatus venoms in the rat isolated atria and anesthetized rats; effect of magnesium and lidocaine

In rat isolated atria, Androctonus australis (Aa), Leiurus quinquestriatus quinquestriatus (Lqq), and L. q. hebraceus (Lqh) venoms produced intense contracture, alterations in the force and frequency of the spontaneous atrial contractions, and delayed afterdepolarizations (DAD). It was shown by means of tetrodotoxin-induced blockade of neurotransmitter release that the contracture and DAD were produced by the action of the venoms on the atrial cell membrane (direct action) while alterations in the force and frequency of the spontaneous atrial contractions were caused by acetylcholine and norepinephrine released by the venoms (indirect action). The irregularities in the spontaneous contractions and DAD were suppressed by magnesium and lidocaine which, however, caused only a small reduction in the intensity of the atrial contracture. The venom-induced DAD was also abolished by ryanodine and intensified by an increase in [Ca2+]0. In anesthetized rats, Aa, Lqq, and Lqh venoms induced hypertension, arrhythmias, and T wave inversion. The arrhythmias included bradycardia, ventricular and supraventricular extrasystoles, unsustained and sustained ventricular tachycardia with torsade de pointes episodes. Magnesium and lidocaine abolished them, and magnesium also counteracted the hypertension. These results suggest that magnesium and lidocaine, particularly magnesium, may be useful in the treatment of the arrhythmias, hypertension, and other disorders associated with Buthinae scorpion envenomation.