Similar results were also obtained for PrTX-I/α-tocopherol and BaspTX-II/suramin structures (dos Santos et al., 2009 and Murakami et al., 2005), leading these authors to choose the alternative assembly when solving both complexed structures. Myographic studies show that MjTX-II (1.0 μM) produced an irreversible and time-dependent blockade of both selleck chemical directly (t1/2 = 40.0 ± 2.3 min, n = 7) and indirectly

(t1/2 = 32.1 ± 4.8 min, n = 5) evoked twitches ( Fig. 5A and B). The present findings were consistent with those already described for other Lys49-PLA2s ( Cavalcante et al., 2007, Gallacci et al., 2006, Randazzo-Moura et al., 2008, Rodrigues-Simioni et al., 1995, Soares et al., 2000, Soares et al., 2001 and Stabeli et al., 2006). Statistical comparison of the indirectly evoked contractions t1/2 of the MjTX-II with those of other Lys49 PLA2s, such as PrTX-I from Bothrops pirajai (t1/2 = 49.0 ± 6.9 min, n = 8) and BthTX-I from Bothrops jararacussu (t1/2 = 40.3 ± 3.5 min, n = 6), obtained at same experimental conditions, indicates that these toxins have similar potency ( Cavalcante et al., 5-FU 2007). In contrast, MjTX-II presents a more potent neuromuscular blockade when compared to MjTX-I from B. moojeni, since at 1.0 μM this toxin depressed in only about

20% the twitches amplitude after 90 min of contact with the preparation ( Salvador et al., 2013). Then, these results indicate MjTX-II has similar or superior neuromuscular blockade action compared to other Lys49-PLA2s. It has been suggested that in vitro neuromuscular blockade effect observed for Lys49-PLA2s may be a consequence of their membrane depolarizing activity Farnesyltransferase ( Gallacci and Cavalcante, 2010). In order to clarify this issue, we performed an electrophysiological study to evaluate membrane depolarizing activity induced by MjTX-II. This technique measures the resting membrane potential of the sarcolemma and has been used as a more direct and sensitive method to

assess the initial events in myotoxicity ( Aragao et al., 2009). The results show a progressive increase in the resting membrane potential of skeletal muscle fibers from 15 min onwards ( Fig. 6) and the increase of the frequency of miniature endplate potentials after 5 min (data not shown), probably as a consequence of the cell depolarization. Taken together, these results show a direct effect of MjTX-II increasing the permeability of the skeletal muscle fibers plasma membrane. Although the Lys49-PLA2s mechanism of action is not yet fully elucidated, several studies point the sarcolemma as the initial target of these myotoxins (Gutierrez and Lomonte, 1995, Lomonte et al., 2003 and Lomonte and Rangel, 2012).