title: Pharmacological study of a new Asp49 phospholipase A(2) (Bbil-TX) isolated from Bothriopsis bilineata smargadina (forest viper) venom in vertebrate neuromuscular preparations.
abstract: The neuromuscular activity of Bbil-TX, a PLA2 with catalytic activity isolated from Bothriopsis bilineata smargadina venom, was examined in chick biventer cervicis (BC) and mouse phrenic nerve-diaphragm (PND) preparations. In BC preparations, Bbil-TX (0.5-10 μg/ml) caused time- and concentration-dependent blockade that was not reversed by washing; the times for 50% blockade were 87 ± 7, 41 ± 7 and 19 ± 2 min (mean ± SEM; n = 4-6) for 1, 5 and 10 μg/ml, respectively. Muscle contractures to exogenous ACh and KCl were unaffected. The toxin (10 μg/ml) also did not affect the twitch-tension of directly-stimulated, curarized (10 μg/ml) BC preparations. However, Bbil-TX (10 μg/ml) produced mild morphological alterations (edematous and/or hyperchromic fibers) in BC; there was also a progressive release of CK (from 116 ± 17 IU/ml (basal) to 710 ± 91 IU/ml after 45 min). Bbil-TX (5 μg/ml)-induced blockade was markedly inhibited at 22-24 °C and pretreatment with p-bromophenacyl bromide (p-BPB) abolished the neuromuscular blockade. Bbil-TX (3-30 μg/ml, n = 4-6) caused partial time- and concentration-dependent blockade in PND preparations (52 ± 2% at the highest concentration). Bbil-TX (30 μg/ml) also markedly reduced the MEPPs frequency [from 26 ± 2.5 (basal) to 10 ± 1 after 60 min; n = 5; p < 0.05] and the quantal content [from 94 ± 14 (basal) to 24 ± 3 after 60 min; n = 5; p < 0.05] of PND preparations, but caused only minor depolarization of the membrane resting potential [from -80 ± 1 mV (basal) to -66 ± 2 mV after 120 min; n = 5; p < 0.05], with no significant change in the depolarizing response to exogenous carbachol. These results show that Bbil-TX is a presynaptic PLA2 that contributes to the neuromuscular blockade caused by B. b. smargadina venom.
authors.affiliation: Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas (UNICAMP), Rua Tessália Vieira de Camargo, 126, Cidade Universitária Zeferino Vaz, 13083-887 Campinas, SP, Brazil.
authors.forename: Rafael Stuani
authors.initials: RS
authors.lastname: Floriano
authors.forename: Victor Corasolla
authors.initials: VC
authors.lastname: Carregari
authors.forename: Valdemir Aparecido
authors.initials: VA
authors.lastname: de Abreu
authors.forename: Bruno
authors.initials: B
authors.lastname: Kenzo-Kagawa
authors.forename: Luis Alberto
authors.initials: LA
authors.lastname: Ponce-Soto
authors.forename: Maria Alice
authors.initials: MA
authors.lastname: da Cruz-Höfling
authors.forename: Stephen
authors.initials: S
authors.lastname: Hyslop
authors.forename: Sergio
authors.initials: S
authors.lastname: Marangoni
authors.forename: Léa
authors.initials: L
authors.lastname: Rodrigues-Simioni
mesh_terms: D000098:Acetophenones / Q000378:metabolism; D000818:Animals; D017837:Bothrops; D002217:Carbachol / Q000494:pharmacology; D002645:Chickens; D003964:Diaphragm / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D055369:Miniature Postsynaptic Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects; D019148:Neuromuscular Blockade; D009469:Neuromuscular Junction / Q000187:drug effects; D054497:Phospholipases A2, Secretory / Q000494:pharmacology*; D010791:Phrenic Nerve / Q000187:drug effects / Q000378:metabolism; D030162:Reptilian Proteins / Q000494:pharmacology*; D014757:Viper Venoms / Q000737:chemistry*
chemical_list: D000098:Acetophenones; D030162:Reptilian Proteins; D014757:Viper Venoms; D002217:Carbachol; C584304:Bbil-TX protein, Bothriopsis bilineata; D054497:Phospholipases A2, Secretory; C006821:4-bromophenacyl bromide