05) than the corresponding IDO inhibitor values obtained without p-BPB). We have recently shown that B. b. smargadina venom produces potent neuromuscular blockade in avian (concentration range: 0.1–30 μg/ml) and mammalian (concentration range: 1–30 μg/ml) nerve–muscle preparations in vitro ( Rodrigues-Simioni et al., 2011). In mammalian preparations, the highest venom concentration

caused marked facilitation of the twitch-tension amplitude and increased the quantal content before the onset of progressive blockade, without altering the resting membrane potential; in avian preparations, the contractile responses to exogenous ACh and KCl were not significantly altered. These findings suggested a presynaptic action in both neuromuscular preparations that was attributed to the PLA2 activity of the venom. We have previously described the biochemical characterization and some biological activities of Bbil-TX, a basic PLA2 isolated from B. b. smargadina

venom, that induces muscle damage in mice (leading to CK release) and is pro-inflammatory, causing edema and stimulating the formation of TNFα, interleukin (IL)-1 and IL-6 ( Carregari et al., in press). As shown here, Bbil-TX also causes neuromuscular blockade in vertebrate nerve–muscle preparations. Indeed, Bbil-TX reproduced the major effects of the venom, i.e., time- and concentration-dependent neuromuscular blockade, with avian preparations being more sensitive than mammalian Selleck PD0332991 preparations (0.5–10 μg/ml vs. 3–30 μg/ml; complete blockade with 10 μg/ml after 40 min in the former while 30 μg/ml caused only 52% blockade after 120 min in the latter). The Bbil-TX-induced blockade involved primarily a presynaptic action, the evidence for which included: (1) a lack of interference with postsynaptic nicotinic receptor function as indicated by unaltered responses to exogenous ACh and CCh, (2) a progressive decrease in the quantal content and MEPP frequency 2-hydroxyphytanoyl-CoA lyase in diaphragm muscle during incubation with Bbil-TX [such a decrease is characteristic of classic presynaptic toxins such as β-bungarotoxin

(Oberg and Kelly, 1976) and crotoxin (Hawgood and Smith, 1989; Rodrigues-Simioni et al., 1990)], (3) an unaltered resting membrane potential (in diaphragm muscle) and unaltered (normal) twitch-tension response in directly stimulated BC and PND preparations preincubated with d-Tc, and (4) an unaltered response to exogenous (KCl), indicating skeletal muscle intactness that was corroborated by a lack of change in the baseline of twitch-tension responses. The contribution of muscle damage to the neuromuscular blockade caused by presynaptically-active Bothrops PLA2 is an aspect that has not been systematically investigated and is likely to vary considerably among these toxins in view of their differing abilities to damage muscle fibers ( Gallacci and Cavalcante, 2010; Correia-de-Sá et al., 2013).