Characterization of presynaptic toxins from venom of the coral snake Micrurus lemniscatus lemniscatus

Abstract

Coral snake (Micrurus spp.) venoms are well-known for their neurotoxicity mediated primarily by a-neurotoxins that act postsynaptically and b-neurotoxins (neurotoxic phospholipases - PLA2) that act presynaptically. Among the Micrurus spp. that have been screened for neurotoxicity, the venom of M. lemniscatus lemniscatus is of particular interest because of its strong presynaptic activity. However, with the exception of the initial studies dealing with the pharmacological characterization of M. l. lemniscatus venom, little is known of the neuromuscular activity of this species. In this project, we intend to purify and characterize the presynaptic neurotoxins of M. l. lemniscatus venom by RP-HPLC, followed by identification of the toxins through sequencing (mass spectrometry) and screening for PLA2 activity and neuromuscular blockade in mouse phrenic nerve-diaphragm preparations in vitro. The mechanisms involved in the blockade by the principal neurotoxin(s) will be examined using a variety of electrophysiological approaches (e.g., recordings of the membrane potential, endplate potential and intracellular potentials, the latter using patch-clamp technology, and extracellular recording of compound action potentials and perineural waves) in conjunction with the assessment of intracellular Ca2+ fluctuations, histological analysis, and imunohistochemical analysis of the expression and distribution of proteins involved in exocytosis. The hemodynamic (arterial blood pressure, respiratory rate), cardiac (isolated atria) and vascular (thoracic aorta) actions of these toxins will also be assessed. The results of this work will contribute to our understanding of the mechanisms involved in the presynaptic neurotoxicity of this venom.