Estudo das atividades neurotoxica e miotoxica de uma fosfolipase A2 basica isolada do veneno total Bothrops marajoensis / Study of neurotoxic and myotoxic activities of a phospholipase A2 isolated from the Bothrops marajoensis venom

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

In the present work, the neuromuscular effects of the toxin Bmaj-9 isolated from the venom of Bothrops marajoensis in the laboratory of chemistry of proteins at Unicamp were studied. This toxin was assayed in biventer cervicis preparations of little chicken, phrenic diaphragm nerve of mice and in gastrocnemius muscles of mice. In birds preparation, Bmaj-9 caused irreversible complete neuromuscular blockade in the concentrations of 5, 10 and 20 µg/mL not affecting the contractures caused by the exogenous addition of Ach (110 µM). Moreover, Bmaj-9 was not very active in the phrenic diaphragm preparation of mice. It has not interfered in the muscular response to direct electrical stimuli in biventer cervicis preparations of little chicken previously curarized. Biochemical assays showed that Bmaj-9 exhibited pronounced phospholipase activity when compared to crude venom. Thus, when preparations incubated with the toxin were submitted to low temperatures (22°C), the absence of the characteristic neuromuscular blocking effect of the fraction was observed. The histological analysis in vitro showed that even having determined a low increase on the release of the creatino-kinase enzyme, low concentrations of this fraction did not cause significant morphological alteration. Nevertheless, in high concentrations some muscular damages in the peripheral region of the muscle were observed. In vivo, Bmaj-9 caused a slight morphological alteration and also a discrete increase on the CK levels after intramuscular injection, showing a positive correlation among the effects of the parameters studies - muscular lesion and CK release. These data obtained with Bmaj-9 are extremely inferior to the ones obtained with bothropic venoms or toxins. The registration of the resting membrane potential showed that Bmaj-9 (10 µg/mL) did not produce depolarization of the muscular membrane and the measurement of the content and quantum size, in phrenic diaphragm preparation of mice, showed that a slight increase on the quantum amount was detected after 15 minutes of incubation. After 60 minutes of incubation, the effect of Bmaj-9 over the content and quantum size values was 70.5 ± 11 and 0.21 ± 0.06 mV, respectively; these values were not significantly different when compared to control values (68.0 ± 8.9 and 0.17 ± 0.04 mV). These values suggest that the blockade of the neuromuscular transmission caused by this toxin in low concentrations is probably due to a pre-synaptic action resulting from the interaction of the toxin with the membrane of the motor nerve terminal.

ASSUNTO(S)

eletrofisiologia neuromuscular junction toxin bothrops toxinas electrophysiology junção neuromuscular

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