Neuromuscular paralysis by the basic phospholipase A(2) subunit of crotoxin from Crotalus durissus terrificus snake venom needs its acid chaperone to concurrently inhibit acetylcholine release and produce muscle blockage

Author(s)

Cavalcante, Walter L. G. ^{[1, 2, 3]} ; Noronha-Matos, Jose B. ^{[3, 4]} ; Timoteo, Maria A. ^{[3, 4]} ; Fontes, Marcos R. M. ^[1] ; Gallacci, Marcia ^[5] ; Correia-de-Sa, Paulo ^{[3, 4]}

Affiliation

^[1] UNESP, Inst Biociencias, Dept Fis & Biofis, BR-18618970 Botucatu, SP - Brazil

^[2] Univ Fed Minas Gerais, Inst Ciencias Biol, Dept Farmacol, Av Antonio Carlos, BR-6627 Belo Horizonte, MG - Brazil

^[3] ICBAS UP, Lab Farmacol & Neurobiol, R Jorge Viterbo Ferreira 228, P-4050313 Oporto - Portugal

^[4] ICBAS UP, Ctr Drug Discovery & Innovat Med MedInUP, R Jorge Viterbo Ferreira 228, P-4050313 Oporto - Portugal

^[5] UNESP, Inst Biociencias, Dept Farmacol, BR-18618970 Botucatu, SP - Brazil

• Document type: Journal article
• Source: Toxicology and Applied Pharmacology; v. 334, p. 8-17, NOV 1 2017.
• Web of Science Citations: 5

Abstract

Background and purpose: Crotoxin (CTX), a heterodimeric phospholipase A(2) (PLA(2)) neurotoxin from Crotalus durissus terrificus snake venom, promotes irreversible blockade of neuromuscular transmission. Indirect electrophysiological evidence suggests that CTX exerts a primary inhibitory action on transmitter exocytosis, yet contribution of a postsynaptic action of the toxin resulting from nicotinic receptor desensitization cannot be excluded. Here, we examined the blocking effect of CTX on nerve-evoked transmitter release measured directly using radioisotope neurochemistry and video microscopy with the FM4-64 fluorescent dye. Experimental approach: Experiments were conducted using mice phrenic-diaphragm preparations. Real-time fluorescence video microscopy and liquid scintillation spectrometry techniques were used to detect transmitter exocytosis and nerve-evoked {[}H-3] -acetylcholine ({[}H-3]ACh) release, respectively. Nerve-evoked myographic recordings were also carried out for comparison purposes. Key results: Both CTX (5 mu g/mL) and its basic PLA(2) subunit (CB, 20 mu g/mL) had biphasic effects on nerve-evoked transmitter exocytosis characterized by a transient initial facilitation followed by a sustained decay. CTX and CB reduced nerve-evoked {[}H-3]ACh release by 60% and 69%, respectively, but only the heterodimer, CTX, decreased the amplitude of nerve-evoked muscle twitches. Conclusion and implications: Data show that CTX exerts a presynaptic inhibitory action on ACh release that is highly dependent on its intrinsic PLA(2) activity. Given the high safety margin of the neuromuscular transmission, one may argue that the presynaptic block caused by the toxin is not enough to produce muscle paralysis unless a concurrent postsynaptic inhibitory action is also exerted by the CTX heterodimer. (AU)

• FAPESP's process: 13/17864-8 - Structural Studies with Neurotoxic Phospholipases A2.
• Grantee: Carlos Alexandre Henrique Fernandes
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/03624-5 - Biological characterization of crotoxin and its basic subunit in the neuromuscular junction: radiochemical and real-time video-microscopy studies
• Grantee: Walter Luís Garrido Cavalcante
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 12/00428-8 - Structural and Functional Characterization of Crotoxin and its Basic Subunit in the Neuromuscular Junction and Influence of Neutralizing Agents
• Grantee: Walter Luís Garrido Cavalcante
• Support Opportunities: Scholarships in Brazil - Post-Doctoral