Poster 261 - A common temperature-dependent step involved in myotoxic and paralyzing effects of

Poster 261. Congresso da Sociedade Brasileira de Toxinologia, 8., Symposium of the Pan American Section of the International Society on Toxinology, 8., 2004, Angra dos Reis, Brasil. Abstracts... J. Venom. Anim. Toxins incl.Trop. Dis., 2004, 10, 3, p.620.

A Common Temperature-Dependent Step Involved In Myotoxic And Paralyzing Effects Of Bothropstoxin-I On Mouse Neuromuscular Preparations

Departments of Pharmacology¹ and Morphology², Institute of Bioscience, University Estadual Paulista UNESP, Botucatu, São Paulo, Brazil.

It has been observed that some myotoxic phopholipases A2 (PLA2s) from snake venoms lack cytolitic effects at low temperature. Bothropstoxin-I (BthTX-I), from Bothrops jararacussu venom, is a phospholipase A2 (PLA2) homologue, devoid of enzymatic activity. Besides inducing severe myonecrosis, BthTX-I promotes paralysis of both directly and indirectly evoked contractions on isolated neuromuscular preparations. We applied an experimental paradigm in order to characterize the steps involved in the toxic effects of BthTX-I on mouse neuromuscular junction. Myotoxicity was assessed by microscopic analysis of extensor digitorum longus muscles; paralyzing activity was evaluated through the recording of isolated contractions indirectly evoked in phrenic-diaphragm preparations. After 90 minutes at 35°C, BthTX-I induced complete and irreversible paralysis, and damaged 30.3 ± 2.7% of muscle fibers. In contrast, no effect was observed when tissues were incubated with BthTX-I at 10°C for 60 minutes and subsequently washed with toxin-free solution and maintained at 35°C. These results indicate that the binding of BthTX-I to the cellular tissue surface is very weak at low temperature and that an additional factor is necessary. However, when tissues were submitted to BthTX-I (10°C for 60 min), and the temperature was elevated to 35°C, omitting the washing step, it was observed muscle paralysis and damage in 39.04 ± 4.2% of muscle fibers. These results indicate that a temperature-dependent step is necessary for BthTX-I to promote both myotoxic and paralyzing activities, suggesting that these effects are closely related. The present data give functional support for the current model of BthTX-I actions, which assumes that it should be inserted into membrane, a step that could be affected by the change in membrane fluidity induced by low temperature.