Functional characterization of a basic D49 phospholipase A2 (LmTX-I) from the venom of the snake Lachesis muta muta (bushmaster).

The whole venom of Lachesis muta muta is preponderantly neurotoxic but moderately myotoxic on the chick biventer cervicis preparation (BCp). We have now examined these toxic activities of a basic phospholipase A(2), 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 microg/ml), 23.6+/-0.9 min (10 microg/ml), 34+/-1.7 min (2.5 microg/ml) and 39.2+/-3.6 min (1 microg/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 microg/ml) significantly reduced contractures elicited by exogenous KCl (20mM), 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 ( approximately 15%). Quantification of myonecrosis indicated 14.8+/-0.8 and 2.0+/-0.4%, with 30 and 10 microg/mlvenom concentration, respectively, against 1.07+/-0.4% for control preparations. The findings indicate that the basic PLA(2) 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 microg/ml). These effects of LmTX-I closely reproduce the effects of the whole venom of L. m. muta in chick neuromuscular preparations.

Neurotoxic and myotoxic actions from Lachesis muta muta (surucucu) whole venom on the mouse and chick nerve-muscle preparations.

Lachesis genus is one of the less studied among others from Viperidae's genera, mainly due to difficulties in obtaining the venom. Accidents by Lachesis snakes cause severe envenoming syndrome, eventually leading victims to shock. This work is part of a comprehensive study aimed at studying the venom and its effects. Herein the neurotoxicity and myotoxicity of L. muta muta venom were investigated on mouse phrenic nerve-diaphragm (PNDp) and chick biventer cervicis (BCp) preparations. For both preparations the time required to venom produces 50% neuromuscular blockade was indirectly concentration-dependent, being for PNDp: 117.6+/-6.5 min (20 microg/ml), 70.1+/-8.6 min (50 microg/ml) and 43.6+/-3.8 min (100 microg/ml), and for BCp: 28+/-1.8 min (50 microg/ml), 30.4+/-2.3 min (10 microg/ml), 50.4+/-4.3 min (5 microg/ml) and 75.2+/-0.7 min (2 microg/ml), (n=5/dose). In BCp, a venom dose of 50 microg/ml significantly reduced contractures elicited by exogenous acetylcholine (55 microM) and KCl (20 mM), as well as increased the release of creatine kinase (442.7+/-39.8 IU/l in controls vs 4322.6+/-395.2 IU/l, after 120 min of venom incubation (P<0.05). Quantification of myonecrosis in BCp indicated the doses 50 and 10 microg/ml as significantly myotoxic affecting 59.7+/-6.2%, and 20.8+/-1.2% of fibers, respectively, whereas 5 and 2 microg/ml that affected 13.5+/-0.8% and 5.4+/-0.6% of fibers, were considered weakly- and non-myotoxic, respectively. We concluded that there are neurotoxins present in the venom, the concentration of which governs its pre- (if low) or postsynaptic (if high) activity. Since myotoxicity in the avian preparation is negligible at lower venom doses, but not neurotoxicity, we suggest that this effect may contribute minimum to the venom neurotoxic effect. The BCp is more sensible than PNDp to Lachesis m. muta venom.