The other end was coupled to an isomeric transducer F-60 connected to a polygraph, both from NARCO BioSystems. The preparation was stabilized for 30 min, ventilated with carbogen (5% CO2 and 95 O2) and changing solution each 10 min. After stabilized, bradykinin at concentrations

16 × 103 to 4 × 103 μM was applied into the system, and the effects registered for 1 min. After that, the preparation was rinsed with Tyrode solution for five times. The bradykinin potentiating activity of kappa-KTx2.5 was evaluated by adding the synthetic peptide at concentrations of 3.19, 6.38 or 9.58 μM to the bath 3 min before the application signaling pathway of 4 × 103 μM bradykinin to the bath. The experiment was done in triplicate. The experimental protocol was approved by the University of Brasilia Animal Care and Use Committee (number 46594/2009). The activity of kappa-KTx2.5 toward Gram-positive Navitoclax (Staphylococcus aureus ATCC 29213) and Gram-negative (Escherichia coli ATCC 25922) bacteria was tested by the broth microdilution assay. The bacteria were grown in Luria-Bertani (LB) medium to the optical density of 0.5 at 600 nm. The highest concentration of the peptide used was 256 μM. Positive and negative controls were carried out with the inoculums plus LB medium and medium only, respectively. The spectrophotometric reading (630 nm) was performed after 12 h incubation time at

37 °C. The docking of the κ-KTx2.5 to the Kv1.2 was performed by AutoDock Suplatast tosilate 4 (http://autodock.scripps.edu/). The κ-KTx2.5 was modeled by Modeller9v6, using the template PDB ID: 1WQD [31]. The Kv1.2 potassium channel coordinates were obtained from its crystal structure PDB ID: 2A79 in its open conformation, and for the docking only the S5 and S6 helices were selected. The interacting portion channel-peptide of Kv1.1, 1.2 and 1.4 are similar. The Kv1.2 channel has a crystal structure, which explains our choice to modeling with the Kv1.2

channel, despite the biological assays done in different in Kv1.1 and 1.4. Both molecules were submitted to atomic charges calculation according to Gasteiger method [10]. The affinity grid maps were built with X-126, Y-126 and Z-126 dimensions, spacing by 0.6 Å. The channel was remained rigid while the peptide flexible, so the docking was carried out through the Lamarkian Genetic Algorithm [20]. For each run were used 15 million evaluations, and the other parameters in default. The results were analyzed with Pymol (http://www.pymol.org/) and the contact maps by the server Sting (http://www.nbi.cnptia.embrapa.br). The fractionation of the crude soluble venom of O. cayaporum by RP-HPLC yielded more than 80 fractions [30]. The component that eluted at 25.9% acetonitrile/0.1% TFA was further purified by analytical RP-HPLC as shown in Fig. 1. The component eluting at retention time of 12.58 min (see inset Fig. 1) was found to be the pure peptide here named κ-KTx 2.