Comparison of the neuromuscular effects of venoms from juvenile and adult Crotalus durissusterrificus in chick nerve-muscle preparations

Pereira, R.S.(1), Belo, C.A.D.(1), Leite, G.B.(1), Cogo, J.C.(2), Simioni, L.R.(1)

(1)Departamento de Farmacologia, FCM, UNICAMP, Campinas, SP, Brasil, (2)Serpentário do CEN, UNIVAP, São José dos Campos, SP, Brasil.

Objectives: The neuromuscular activity of venoms from juvenile and adult South American rattlesnakes (Crotalus durissus terrificus) was compared using chick isolated biventer cervicis muscle preparations. Methodology: Venoms were collected from juvenile and adult snakes by manual extraction and desiccated. Male HY-LINE W36 chicks 4-8 days old  were  anesthetized with cloralhydrate (300 mg/kg, i.p.) and the muscles were removed and mounted in a 5 ml organ bath (Ginsborg and Warriner, 1960) containing Krebs solution (pH 7.5, 37°C) of the following composition (mM): NaCl118.7, KCl 4.7, CaCl₂ 1.88, KH₂PO₄ 1.17, MgSO₄ 1.17, NaHCO₃ 25.0, and glucose 11.65 aerated with 95% O₂ and 5% CO₂. Stimuli were delivered via a bipolar platinum ring electrode (0.1 Hz, 0.2 ms, 8 V, GRASS S48 stimulator) and the contractions were recorded  on a Gould RS 3400 physiograph. Contractures to exogenous acetylcholine (ACh, 60 and 120 mM for 60 s) and KCl (13.4 mM for 130 s) were obtained to test for neurotoxic and  myotoxic activities (Harvey et al., 1994).  After a 20 min stabilization, ACh, KCl and venoms were added to the bath. ANOVA/MANOVA for repeated measures was used to test for significance. Results: The venoms of juvenile snakes tested at five concentrations (0.5, 1, 5, 10 and 20 mg/ml) produced 50%    neuromuscular blockade in 36±7,32±4,20±3,20±1 and 19±3 min, respectively (mean±SEM, n=3 each). At these same concentrations, 50% neuromuscular  blockade was observed with venoms from adult snakes after 40±3,35±4,24±2,27±3 and 24±2 min, respectively (n=3 each).None of the venoms affected the contractile responses to exogenous Ach and K⁺. Conclusion: The venoms of juvenile and adult  C. d. terrificus showed similar potencies in chick neuromuscular preparations, and none of them were  myotoxic, as shown by their inability to affect contractures to KCl.

Financial support: CNPq

CORRESPONDENCE TO:

Cháriston André Dal Belo, Rua João Jacob Rohwedder, 19, Sumaré, SP, CEP: 13.170-310, Brasil, Email: charistondb@yahoo.com.br