Isolation And Partial Characterization Of A New Toxin (Bt II-2) From Bothrops alternatus Venom Active In Chick Biventer Cervicis Preparations. 

¹Barros, J.C.; ¹Borja-Oliveira, C.R.; ¹Hernandez-Oliveira, S.S.; ²Ponce-Soto, L.A.; ³de Santis, L.H.; ²Marangoni, S.; ⁴Corrado, A.P.; ¹Rodrigues-Simioni, L.

1 Depart. Pharmacology, Faculty of Medical Sciences; 2 Depart. Biochemistry and 3 Depart. Histology and Embryology, Institute of Biology/UNICAMP; 4 Depart. Pharmacology, Faculty of Medicine/USP, Ribeirão Preto/SP, Brazil.

The venoms of various Bothrops species cause neuromuscular blockade in nerve-muscle preparations in vitro. In this work, we isolated a new toxin from Bothrops alternatus venom that inhibits neurotransmission in chick biventer cervicis preparations. Fractionation of B. alternatus venom (10 mg) by reverse-phase HPLC on a C18 m-Bondapack column yielded an active peak containing the toxin BtII-2. In SDS-PAGE, the toxin migrated as a single band with a molecular mass of 14 kDa. In chick biventer cervicis preparations, BtII-2 (0.1, 0.5, 1, 5, 10 and 20 mg/ml; n=7 each) produced concentration-dependent, irreversible twitch-tension blockade without affecting the muscle responses to exogenous ACh and KCl. The time (in min) required to produce 50% neuromuscular blockade at the concentrations indicated above was 65±0.9, 41±0.4, 35±0.6, 24±0.3 22±0.4 and 20±0.8 (mean+S.E.M.), respectively. BtII-2 (1 mg/ml) did not interfere with the membrane resting potential but caused a slight initial, transitory increase in the miniature end-plate potentials (mepps) followed by a progressive and total blockade of mepps. Btll-2 caused morphological alterations in the muscle fibers, with a concentration of 1 mg/ml being more potent in inducing hypercontraction and myofibrillar disorganization than the venom (100 mg/ml). Together, these results  indicate that BtII-2 acts primarily at presynaptic sites.

Support : CAPES and FAPESP/UNICAMP

Correspondence to: simioni@unicamp.br