Biochemical and pharmacological studies on a lethal neurotoxic polypeptide fromPhoneutria nigriventerspider venom

摘要

Fractionation ofPhoneutria nigriventerspider venom by gel filtration and HPLC yielded a few fractions that induced different effects when administered intraperitoneally in mice. One of these fractions, PF3, was chemically characterized as a cysteine-rich polypeptide of ∼8360 MW. Administered at 0.1 mg/kg, i.p., PF3 induced a progressive paralysis and death of mice within 30 minutes. Partial sequence analysis of PF3 revealed certain homologies with other spider toxins already described, particularly omega-AGAIIA (60) fromAgelenopsis aperta. Pharmacological characterization carried out in superfused chopped rat striatal tissues preloaded with 3H-Dopamine (3H-DA) showed that PF3 (0.1 μg/ml) decreased the 3H-DA release induced by 20 mM K+or 100 μM glutamate without changing the basal release. At 1 μg/ml, PF3 inhibited 33 of the basal release of 3H-DA; the transmitter release stimulated by K+or by glutamate was reduced by respectively, 87 and 77 of corresponding control values. PF3 (0.1 μg/ml) altered the doseresponse curves of glutamate (1 μM−10mM), by reducing by 36 of its maximal effect. Naloxone (1 μM) did not influence the effect of PF3. The results indicate that PF3 inhibits the 3H-DA release induced by membrane depolarization or that mediated by NMDA glutamate receptors. These data suggest that the mechanism of action of PF3 may involve a blockade of Ca2+channels as well as a direct effect on the exocytotic