Functional characterization of a basic Asp49 phospholipase A2 (LmTX-I) from the venom of the snake Lachesis muta muta (bushmaster)
Damico, D. C. S.1; Bueno, L. G. F.3; Rodrigues-Simioni, L.3; Marangoni, S.1; Cruz-Höfling, M. A.2; Novello, J. C1.
1Department of Biochemistry and 2Department of Histology and Embryology, Institute of Biology, State University of Campinas (UNICAMP), P. O. Box 6109, Zip code 13083-970, Campinas, SP, Brazil and 3Department of Pharmacology, Faculty of medical sciences, State University of Campinas (UNICAMP), Campinas, SP, Brazil.
The whole venom of the snake Lachesis muta muta at low concentration (2 mg/ml) exhibited potent neurotoxicity, and myotoxicity in chick biventer cervicis preparation (BCp) was patent only at concentrations higher than 10 mg/ml. We have now examined these toxic activities of a basic phospholipase A2, LmTX-I, isolated from the whole venom. LmTX-I caused a significant concentration dependent neuromuscular blockade in the BCp. The time to produce 50% neuromuscular blockade was 14.7 ± 0.75 min (30 mg/ml), 23.6 ± 0.9 min (10 mg/ml), 34 ± 1.7 min (2.5 mg/ml) and 39.2 ± 3.6 min (1 mg/ml), (n = 5/concentration; p < 0.05). Complete blockade with all tested concentrations was not accompanied by inhibition of the response to ACh. At the highest concentration, LmTX-I (30 mg/ml) significantly reduced contractures elicited by exogenous KCl (20 mM), increased the release of creatine kinase (1542.5 ± 183.9 IU/L vs 442.7 ± 39.8 IU/L for controls after 120 min, p < 0.05), and induced the appearance of degenerating muscle fibers. Quantification of myonecrosis indicated 14.8 ± 0.8 % and 2.0 ± 0.4 %, with 30 and 10 mg/ml venom concentration, respectively, against 1.07 ± 0.4 % for control preparations. The findings indicate that the basic PLA2 present on venom from L. m. muta (LmTX-I) possesses a dominant neurotoxic action on isolated chick nerve-muscle preparations, whereas myotoxicity was mainly observed at the highest concentration used (30 mg/ml). These effects of LmTX-I closely reproduce the effects of the whole venom of Lachesis muta muta in chick neuromuscular preparations.
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