BIOCHEMICAL AND PHARMACOLOGICAL STUDIES ON A LETHAL NEUROTOXIC POLYPEPTIDE FROM PHONEUTRIA NIGRIVENTER SPIDER VENOM

Fractionation of Phoneutria nigriventer spider venom by gel filtration and HPLC yielded a few fractions that induced different effects when administered intraperitoneally in mice. One of these fractions, PF3, w as chemically characterized as a cysteine-rich polypeptide of similar to 8360 MW. Administered at 0.1 mg/kg, i.p., PF3 induced a progressive paralysis and death of mice within 30 minutes. Partial sequence analy sis of PF3 revealed certain homologies with other spider toxins alread y described, particularly omega-AGAIIA (60%) from Agelenopsis aperta. Pharmacological characterization carried out in superfused chopped rat striatal tissues preloaded with [H-3]-Dopamine ([H-3]-DA) showed that PF3 (0.1 mu g/ml) decreased the [H-3]-DA release induced by 20 mM Kor 100 mu M glutamate without changing the basal release. At 1 mu g/ml , PF3 inhibited 33% of the basal release of [H-3]-DA; the transmitter release stimulated by K+ or by glutamate was reduced by respectively, 87% and 77% of corresponding control values. PF3 (0.1 mu g/ml) altered the dose-response curves of glutamate (1 mu M - 10 mM), by reducing b y 36% of its maximal effect. Naloxone (1 mu M) did not influence the e ffect of PF3. The results indicate that PF3 inhibits the [H-3]-DA rele ase induced by membrane depolarization or that mediated by NMDA glutam ate 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 machinery.